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A STUDY OF THE EFFECTS THERMAL PROCESSING, TEMPERATURE AND EXTERML ACID CONCENTRATION ON THE D.C. CONDUCTIVTYOF NAFION@ 117 MEMBRANES

Naim Ghany

A thesis submitted in conformity with the requirements for the degree of Master of Applied Science

Graduate Department of Chernical Engineering and Applied Chemistry University of Toronto

Clcopyright by Naim Ghany (2000)

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ABSTRACT

TITLE: A S'I"LTDY OF THE EFFECTS OF THERMAL PROCESSING, TEMPERATURE AND

EXTERNAL AClD CONCENTRATION ON THE D.C. CONDUCTWITY OF NAFION@ I 17

MEMBRANES.

AUTHOR: NAIM GHANY

DEGREE OF MASTER OF APPLIED SCIENCE

GRADUATE DEPARTMEbT OF CHEMICAL ENGiNEERING AND APPLIED CHEMISTRY

üNIVERS ITY OF TORONTO (2000)

The process of thermal bonding of Nafion@ 1 17 polymer rlectrolyte membranes to

electmdes and the effects of the thermal bonding process on the ionic conductivity of the

membranes were investigated. The thermal bonding process was investigated by first constructing a

hot pressing unit. The press was then used to determine which combination of temperature. pressure

and time resulted in the strongest thermal bond.

Membrane ionic conductivity was investigated using both d.c. and a.c. methods. The

conductivity of the various membrane configurations was measured (using both methods) in

different concentrations of H2S04 and in 0.6 M KCI and at different temperattues.

The mechanicall y strongest thermal bonding occurred under hot pressing conditions of

1 70°C. 1 1 MPa for 90 seconds. Conductivity measurements showed that thermal bonding does not

introduce an interfaciai resistance between membranes. The data show that as the membrane

thickness increased so did the conductivity. It was also shown that heating the membrane above its

glass transition temperature improved the conductivity of Nafion@ 1 17 membranes. The d.c.

method used was determined to be accurate in measuring Nafion@ conductivity as the data are in

good agreement with those of other worken.

ACKNOWLEDGEMENTS

I wish to thank Professor F. R. Foulkes for his guidance, which has k e n of great help

throughout this thesis.

I would also like to thank Dr. Joy Congson, Dr. John Graydon Paul Jowlabar, Shahram

Karimi and Selwyn Firth for the help and advice in various areas of this project that they have

kindly given me.

Finally, 1 would like to thank rny family for the support that they have given me throughout

my p d u a t e studies.

TABLE OF CONTENTS

Abstract

Acknowledgements

Table of Contents

List of Tables and Figures

Introduction

Background

Theory

Basic Fuel Cell Operation

Ionic Conductivity

Hot Pressing

Conductivity Measurements

Objectives

Experimental Details

Hot Press Design and Construction

MEA Fabrication and Testing

Membrane Conductntity Testing

Results and Discussion

MEA Fabrication and Testing Results

D.C. Conductmty Results

D.C. Measurement Results

Cornparison with Other Shidies

D.C. ConduetMy in Pure Water

Page No.

ii

. .. 111

iv

vi

A.C. vs D.C. Results

Effect of Temperature on Membrane Conductivity

Conclusions

References

Appendir 1

Section 1. D.C. Conductivity Data

Section 2. Sample Calculation of D.C. Conductivity

Section 3. Membrane Resistance Data

Section 4. Data and Calculations for Nafion@ 117 in Pure H20

Appendix 2. A.C. Impedance Data and Calculations

Appendix 3

Section 1. Membrane Titration Data

Section 2. Sample Calculation for Ion Exchange Capacity

Appendu 1

Section 1. Membrane Water Uptske Data

Section 2. Calculation of Membrane Water Content

Appendix 5

Section 1. Calculation of Activation Energy

Section 2. Calculation of Stagnant Layer Resistance

Section 3. Calculation of Ion Exchange Site Concenti~tion

Section 4. Graphite Electrode Fabrication

Section 5. Equipment Supplier Information

LIST OF TABLES AND FIGURES

TABLES

Table 1. Resuits of MEA Fabrication Tests

Page No.

28

Table 2. D.C. Conductivity Data at 25°C 30

Table 3. Membrane Water Content Results 37

Table 4. Membrane Titration Results 39

Table 5. D.C. Conductivity Data Surnmary

Table 6. Cornparison of A.C. and D.C. Conductivity Data

Table 7. Summary of A.C. Conductivity Data

Table 8. Conductivity Data for Nafion0 1 17 in 1 .O M H2S04 and 0.6 M KCl at Varying Temperatures

Table 9. Activation Energy Data 50

Table 10. Membrane Resistance Data for D.C. Conductivity Measurements 92

Table 11. Membrane Resistance Per Unit Thickness 92

Table 12. A.C. Conductivity Data as Measured by Conductivity Meter 94

Table 13. Membrane Titration Data 95

Table 14. Membrane Water Content Data 97

FIGURES

Figure 1. Fuel Ce11 Operating Principle

Figure 2. Nafion@ Structure

Figure 3. The Two Phase Model

Figure 4. The Core SheIl Model

Figure 5. Wheatstone Bridge Circuit

Figure 6. Front and Top Views of Upper Platen

Figure 7. Front and Top Views of Lower Platen

Fipre 8. Hot Press Photograph

Figure 9. Diegram of D.C. Sliding Cell

Figure 10. Cross-section Area of D.C. Sliding Ce11

Figure 11. Schematic of Expenmental Set Up for D.C. Conductivity Measurements

Figure 12. Front View of Clamp Ce11 Used for A.C. Conductivity Measurements

Figure 13. Cross-section View of the Contact Area of The Clamp Ce11

Figure 14. Log Conductivity vs HzSOj Concentration for Al1 Membranes

Figure 15. Log Conductivity vs Log HzSOJ Concentration for a Single Processed Membrane

Figure 16. Log Conductivity vs Log HzSOJ Concentration for a Membrane Heated to 1 70°C

Figure 17. Log Conductivity vs Log H2S04 Concentration for a Single Membrane Composite

Figure 18. Log Conductivity vs Log HISOl Concentration for a Two Membrane Composite

Figure 19. Log Conductivity vs Log &S04 Concentration for a Three Membrane Composite

Fipre 20. Log Conductivity (calculated) vs HzS04 Concentration (up to 0.1 M) for Al1 Membranes.

Figure 21. Conductivity vs Temperature. 1 .O M H2SO4 and Nafion@ 1 17 in 1 .O M H2S OJ

Figure 22. Conductivity vs Temperature. Nafion@ 11 7 in 0.6 M KCl

Figure 23. Log Conductivity vs Lnverse Temperature. l .O M H2S04 and Nafion@ 1 17 in 1 .O M HzSOJ

vii

Fipre 24. Log Conductivity vs Inverse Temperature. Nafion@ 1 17 in 0.6 M KCl

Figure 25. D.C. Conductivity Sample Data Plot

Fipre 26. Membrane Water Content Sample Data Plot

Fipre 27. Conductivity vs Inverse Temperature sample Data Plot

viii

INTRODUCTION

BACKGROUND

Fuel cells are devices that convert the chernical energy of a fuel and an oxidant

directly to d.c. electricity. They differ fiom prirnary and secondary cells in that primary and

secondary cells store electricd energy within their electrodes, whereas a fuel ce11 is an energy

conversion device.

All fuel cells operate in the same manner. The fuel and oxidant are fed through

electrodes that are separated by an ion-conducting electrolyte. To complete the circuit the

electrodes are comected electrically through an extemal load such as a motor. The flow of

current is supported by the flow of ions in the electrolyte and by electrons in the extemal

circuit. The ionic species transported during current Bow depend on the type of Fuel cell. Cells

that use acidic electrolytes (such as phosphoric acid or solid polymer electrolyte fuel cells)

transport hydrogen ion (m. in those that use an aikaline electrolyte (usually KOH). hydroxyl

ions (OH3 are transported. Carbonate CO^'^ and oxide (023 ions are transported in molten

carbonate and solid oxide fuel cells. respectively. '" In this thesis the solid polymer electrolyte

(SPE) fuel cell will be discussed.

Although fuel cells have existed for over one hundred and fiRy years, SPE fuel cells

did not appear until 1959, when Generai Electric (GE) introduced the first SPE fuel cells for

NASA to be used in the Gemini space program!" GE b d t fuel cells for both NASA and the

U.S. military. The Gemini spacecraft used two I -kW GE units as their prirnary power

sources. These cells used a polystyrenesuifonic acid membrane as the electrolyte. 1969 saw

the introduction of Nafion@ membranes as the electrolyte in SPE fuel cells. Nafion@ is a

sulfonated Buoropolymer that was introduced in 1968 by DuPont. Ail early SPE fuel cells

used pure hydrogen as the fuel and oxygen as the oxidant. Fuel cells that used hydrocarbons

directly or indirectly as the source of hydrogen were not seen until GE developed a 1.5-kW

plant that used J P 4 jet fuel during 1966 - 1968. In 198 1 GE was commissioned by the Los

Alamos National Laboratory to do a study on an indirect (stem refonned) methanol-air

power plant for ûansportation applications!2'

In the 1970's and the early 1980's fuel ce11 research in the U. S. was slowed

considerably due to a lack of governent funding. However, this al1 changed in the mid to

late 1980's when it was realized that due to pollution problems, cleaner and more efficient

energy production methods were needed. The resulting increase in government spending on

research projects led to several companies developing fuel ce11 technologies. At present. the

Company furthest ahead in the cornmercialization of SPE Fuel ce11 technology is Ballard

Power Systems, of Vancouver. Canada

In 1983 Ballard Power Systerns began developing SPEFC technology with financial

assistance from the Canadian Department of National Defense. "' Since then they have

become the world leaders in SPEFC technology. In recent years Ballard has fomed alliances

with several automobile manufacturen. including GM, Nissan, Honda, Volkswagen A.G and

Volvo A.B., in order to develop their SPEFC technology for transportation applications. In

December 1997, Ballard announced a the-way alliance with Ford Motor Company and

Daimler-Benz (now DaimlerChrysler) that saw an injection of $650-million into Ballard. In

1997 they were also in the process of delivering orders for six SPEFC-powered buses to the

Chicago and British Columbia Transit Authorities. in May 1999. DairnlerChrysler unveiled

its latest fuel ce11 - powered concept car, the NECAR4. The NECARJ uses the Ballard Mark 7

fuel cell. Ford also recently introduced a vehicle (the P2000) that is powered by the Ballard

Mark 7 fuel cell. It has been projected that both Ford and DaimlerChrysler will offer fuel ceil

- powered vehicles for commercial sale by the year 2004. '') Ford is also parnien with

International Fuel Cells of Windsor, Connecticut and the U. S. Department of Energy in

developing a 50 kW SPEFC for use in automobiles. ("

Fuel cells are also being developed as stationary power plants and as replacements for

conventional batteries in consumer electronics. The development of Fuel ce11 power plants is

k ing pursued because they c m be used either in large, cenaalized power plants or as power

plants in individual homes. Several fimis, including Ballard, GE, Plug Power. H Power

Corporation and Hydrogenics Corporation are pursuing the development of SPEFCs for

stationary applications. Currently Ballard. in cooperation with B. C. Hydro. is testing a 250

kW power plant with a naniral gas feed. Ballard is hoping to offer the units commercially by

200 1. Plug Power has installed a 7kW unit at a home in Latharn. N. Y. GE is also in

partnenhip with Plug Power in the development of SPEFCs for home use. They plan to install

the first units in early 2001. Hydrogenics Corporation has recently patented the HyTEF@ fuel

ce11 based portable generator for use under extreme environmental conditions. They are also

developing stationary fuel cells for commercial and industriai buildings, fuel cells for portable

generaton and cells for unintemptible power supplies!35' The development of fuel cells for

consumer electronics is still in its early stages. and no commercial or test models are expected

soon.

Although fuel ce11 technology looks prornising, there are several problems that need

resolution before the technology becomes economically viable. The most important of these

problems is the hi& cost of the fuel cells. Several companies have estimated that fuel ce11

costs would have to be below $ L000IkW and below $50/kW for stationary power generation

and transportation applications. respectively. in order to be cornpetitive with current

technologies. Currently it is estimated that SPEFC costs are over %5000/kW. The bulk of this

($3800/kW) can attributed to the cost of ce11 manufacture. The remaining portion

($1200/kW) is materiais costs. "' It is believed that as ce11 production increases.

manufacturing costs will decrease significantly because of the economic advantages provided

by mass production. The most expensive ce11 components are the membrane electrode

assemblies (MEAs), on account of the hi& cost of both the platinum electrocatalyst and the

polymer electrolyte membrane, both of which comprise the major portion of the materials

cost.

The worldwide demand for plathum has been predominantly for its use as an

automobile exhaust cataiyst (42%) and in jewelry (37%). The remaining 21% of the demand

has k e n for its use in the electrical, glass, petroleum and chernical industries as well as

platinum absorbed by investment. "' The cost of platinum is high because of its scarcity.

Accordingly, the platinum content of fuel cells must be reduced if the technology is to be

cornpetitive. The typical platinum content of an MEA has been as hi& as 1 mg/crn2. which

translates to a plathum cost of $125 (US) per ce11 for a 780 cm' cell. Electrodes with much

lower Pt loading (approximately 0.15 mg/cm2) are currently available. '" This represents a

decrease in the Pt loading by a factor of 27.

The polymer electrolyte most commonly used in fuel cells is Nafion@, manufactured

by the E. 1. DuPont de Nemours Company. The current price of Nafiion0 is appmximately

$800(~~)1m'. which translates to a cost of $95(US)/kW. DuPont estimates that the price of

Nafion@ should drop by a factor of 10 if enough Nafion@ can be sold for use in 250.000

automobiles per year. "' Other ways of reducing the cost of the electrolyte include improving

the manufacniring process and creating newer. cheaper membranes. Ballard is addressing the

latter with the formation of Ballard Advanced Materials (BAM), which is seeking to develop

a lower cost non-perfluorinated membrane based on a trifluorostyrene monomer. Large-scale

production costs are estimated to reach $1 7(US)/kW based on a volume demand. "'

The other major problems facing fuel ce11 commercialization are the production,

storage and distribution of the fuel. For stationary purposes, the fuel can be n a t d gas, which

would be converted to hydrogen and carbon dioxide by a small reformer unit. This can be

achieved without much difficulty. since there is an extensive gas distribution network already

in existence. '6' The fuel problem is more difficult to solve for automobiles becaw there are

space and weight limitations that need to be addressed. In an automobile, where there is

limited space for the fbel cell, reformer and fbel storage tanks; the size of the fuel tanks, type .

of fuel and overall weight of the system are major concerns. It is considered impractical to

store compressed or liquefied hydrogen in an automobile fuel storage tank because the size

and weight of the tanks would be too great. Because of this, systems similar to that descnbed

previously, where a fuel is stem refomed to produce hydrogen and carbon dioxide. are being

de~eloped.'~' Using such a system. a conventional liquid fuel such as methanol (currently the

preferred liquid fuel feed) could be used and the hie1 tank would be of a size similar IO that

currently used in conventional cars. Gasoline is seen as a viable alternative to methanol

because there is a tremendous gasoline production capacity around the world that is already in

place. Arthur D. Little Inc.. in conjunction with Chrysler (now DaimierChrysler) and various

research institutions in the U. S. have demonstrated a new catalytic reformer technology for

the reformation of gasoline. To date the system has been tested successfilly with ethanol.

Gasoline is dificult to reform on account of the presence of catalytic poisons such as sulphur.

It is estimated that the use of gasoline as the reformer feed will decrease the tirne required for

the commercialization of Fuel ce11 technology. "' Despite th;: negative commercial conditions that fuel ce11 markets face, there are

several factors that favour their development. The most important of these is that the fuel cell

c m meet the growing need for a power source that bas hi&-energy conversion efficiency and

is nonpolluting. Also, the costs ïncurred by ernissive pollution (e.g. health and cleanup costs)

would be avoided with the use of fuel cells. This economic benefit is seldom recognized.

In 1997 at the global warming conference in Kyoto, Japan, it was agreed that by the

year 20 1 1, the industrialized nations would decrease greenhouse gas emissions by 5.2% fiom

the 1990 levels. One of the main greenhouse gases is carbon dioxide, the production of which

is directly linked to hydrocarbon-based fuel consurnption. Lt has been estimated that 20% of

al1 CO2 emissions come from vehicles. Reductions in other atmospheric pollutants such as the

oxides of sulphur (SO,) and of nitrogen (NO,) also are sought. '3

Due to the seventy of smog pollution, some jurisdictions have enacted strict emissions

standards and are requiring automobile manufachiren to offer nonpolluting, zero emission

vehicles for sale. Most notable is California where the law States that by the year 7003. 10 %

of new vehicles sold rnust be nonpolluting, zero emissions vehicles. "' A study by Volvo A.

B. suggests that. depending on the fuel and its source, the use of fuel cells can greatly reduce

the emissions of pollutants. 'Io'

There is thus rnuch optimism regardhg the commercial viability of fuel cells;

however, there are still major obstacles that need to be overcome before hiel ce11 technology

becomes widely available and accepted.

THEORY

Basic Fuel Celi Operation

The fuel used by the SPE niel ce11 is hydrogen; during the operation of an SPE fuel

cell, this fuel is fed to the anode and the oxidant (air or pure oxygen) is fed to the cathode. At

the anode, the incoming hydrogen gas dissociates into hydrogen ions and electrons. The

hydrogen ions migrate through the polymer electrolyte to the cathode, where they react with

the electrons from the hydrogen dissociation (which are transported through the extemal

circuit) and oxygen gas to form water. This is illustrated in figure 1 ."

Load

Anode \

EZectro(vte

ANODE: H~ Zr + 2e-

CATHODE: 2b2 + 2 s + 2e-- H20

OVERALL: Ht + @2 -* H20

Figure I: Fuel ce11 operoring principle

Porous Cathode

As previously mentioned. the polymer most commonly used in SPE fuel cells is

DuPont's NafionB. Nafion has a fluorinated polyrner backbone; the pendant side chahs that

cary the sulfonic acid ion exchange sites (SO33 are attached to this main backbone with a

vinyl ether linkage as shown in figure 2. ' "'

Figure 2 Nafion structure

The interna1 structure of NaiTon@ has been studied using many methods, including IR

spectroscopy. small angle X-ray scattering (SAXS) and wide angle X-ray diffraction

(wAxD)!"" SAXS studies have shown that within Nafion@ there are two phases: a

hydrophobic phase and a hydrophilic phase. The hydrophobic phase consists of the

fluoropolymer backbone of the ionorner. the hydrophilic phase consists of the ion exchange

sites that retain water through ion-dipole interactions. It has been shown that many of the ion

exchange sites arrange themselves into clusters, which are connected to each other in a

nerwork via other ion exchange sites that have not clustered. "" SAXS studies have show

that both the number of ion exchange sites per cluster and the cluster size are funftions of the

water content of the polymer. "'" For ionic conduction to take place, the Nafion@ must be

hydrated. Ionic conduction is achieved by the migration of mobile hydrated hydronium ions

via the exchange sites in the clusters and the "connecting channels" through the network. This

migration is driven by an electromotive force.

A theoretical mode1 for the conduction of ions through polymer electrolytes was first

presented by Eisenberg in 1970. '13' Theoretical structural models that are specifically

applicable to Nafion@ have been proposed by MaUntz et ai, 'ln Gierke et al. '15' Cooper et al

(16' and MacKnight et al. " " In their 1982 paper, using SAXS midies. Hashimoto et al "'' were

the h t to confirm the presence of ion clusters in Nafion@. They also showed that there are

two rnodels that can explain the data: The first model, called the Two-phase model (figure 3).

was fim put fonvard by Cooper et al 06' to explain clustering in carbon-based carboxylated

ionomers. in the two-phase model the ion clusten are dispened in a matrix that comprises

fluorocarbon chains and non-clustered ions (an intemediate ionic phase). The data were

attributed to an inter cluster intertèrence, retlecting an average inter cluster difference. The

second model, proposed by Macknight et al "6' is called the Core-shell model (figure 4) . In

this model, the ion cluster (an ion-rich core) is surrounded by a shell that is p n m d y

composed of fluorocarbon chains. Gierke et ai also have performed SAXS studies on

NafionB. and their data also support ion clustenng in Nafion@. ""

1 Ion' Intermedi<rre phase conlaining ion pairs andjluorocarbon chaim

Figure 3: The Two phase mode!

I ion c h t e r (core)

intermediace phake conraining ion pairs andfluorocarbon chains

Figure 4: Tlie Core shell model

Hot Pressing

h order to fabricate the membrane electrode assembly (MEA), the Nafion@

membrane typically is bonded to the electrodes by hot pressing. This is done in order to

pemianently bond the membrane to the graphite-based electrode so as to ensure the integrity

of the MEA. For this process to be effective, the polymer must melt in order for it to bond

with the eiectrode. Hot pressing typically is carried out at temperatures. pressures and

pressing times ranging fiom 120 - 1 80°C, 4.1 - 1 1 MPa and 30 - 90 S. (17 -"' Of the three

parameters, the temperature range is the most critical. Kyu et al have performed dynarnic

mechanicd anaiysis (DMA) on Nafion0 sulfonate membranes which shows a thermal

reiaxarion ar approximately 140iC and one at 240°C. :"' The thermal relaxation at 1 40°C can

be attributed to the melting of copolymen that have an average equivalent weight that is the

same as that of the polymer. It also can be associated with the matrix glass transition

temperature ( r , ,). which may be defined as the lowest temperature at which chah segments

of the polymer will undergo translational and rotational movements. '"' The molecular

weight. ionic group size, intermolecular forces (such as those caused by hydrogen bonding)

and ionic interactions affect the tg ,. As a result, Nafion@ polymers of diffenng equivalent

weights will have slightly different tg , S. Essentidly. this means that the polymer will start to

meit &er it has been heated to approximately 140°C. '"' Accordingly, hot pressing should be

carried out at temperatures above 140°C: however melting may occur at temperatures that are

lower than this. owing to the factors listed above. The time and pressure required to

effectively bond a polymer membrane to an electrode are governed by the rate at which the

membrane melts, which in turn is govemed mainly by the pressing temperature.

Conductivitv Measurements

Electrolytic conductivity measurements can be carried out using both a.c. and d.c.

methods. The d.c. method is simpler but more time consuming than the a-c. method. To

measure conductivity using the d.c. method, a constant current is passed through the polymer

electrolyte membrane, which is contained in an electrochemical clamp type cell. The resuiting

IR drop through the membrane then cm be used too caiculate the conductivity using the

equation:

where 1 is the membrane thickness (m), A is the membrane area through which current flows

(m'), 1 is the (unidirectional) current (A), V is the voltage drop through the membrane (V) and

a is the membrane conductivity (~ .m*') . Membrane conductivity also cm be determined by

ac. impedance. An advantage of this method is that information about the nature of the

impedance is provided over a broad frequency range, so that the region dominated by ionic

conductance c m be isolated. '=' The ac . impedance method requires that the ce11 containing

the membrane be comected into a wheatstone bridge circuit. The basic setup is shown in

figure 5.

B

Figure 5: A wheatstone bridge circuii

RI, R2, and R3 are variable resistors, and R, is the ce11 resistance. A sinusoidd

altemating voltage at either Iow or high frequency is applied across points A and C. and a nul1

detector (ND) is comected across points B and D. Meanirements are taken at different

fiequencies to determine the exact nature of the impedance. At high fiequencies, there are

components of the measured impedance that can be attributed to inductance and capacitance

effec& c 4 . m

The ac. ce11 that is used to determine membrane conductivity can be configured to use

either the four point probe method or the two point probe method. In the four point probe

method, the membrane typically is clamped into the ce11 and is in contact with two current - canying electrodes at the ends of the membrane. Potential ditTerence measurements are taken

using two imer electrodes. In this configuration the current runs dong the length of the

membrane (the membrane k ing i s ~ t r o ~ i c ) . ' ~ ' In the two-point probe method. the electrodes

are set up so that the membrane is sandwiched between them. The curent runs through the

thickness of the membrane and measurernents are taken using the current canying electrodes.

'2'" The resistance fiom both the four and two probe methods is detennined by an analysis of

the irnpedance plot (Bode plot) generated by the response of the ce11 to the a. c. input. The ce11

1 factor (- ) used in the calculation of conductivity for the four point probe method is

A

cdculated using equation 2; '"'

where ES is the electrode separation - the distance between the measurement electrodes and A

is the electrode area (membrane thickness x width). Once this ce11 factor is known, membrane

conductivity then can be calculated using equation 1.

To date, most of the impedance studies carrïed out on electrolytic membranes have

employed the ac. method. which is easier to use than the d.c. method. However. the d.c.

method is supenor because the data are not dependent upon the analysis of a plot with reaf

and imaginary parts. In this study, the d.c. method was used for these reasons and, also,

because during fuel ce11 operation the cunent flowing through the membrane is direct and not

altemating. M e f o r e it is preferable to investigate membrane characteristics using the direct

current method, suice this is most representative of the current flow through the membrane

during actual fuel ce11 operation.

OBJECTIVES

To design and construct a hot press that could be used to evaluate the conditions under

which the bonding of electrodes to electrolyte membranes to produce MEAS takes

place.

To detemine the optimal set of hot pressing conditions. Combinations of pressing

temperature. pressure and time were to be evaluated.

To determine of the effects of hot pressing on the electrolytic conductivity of

Nafion@ membranes.

To determine the conductivity of Nafion@ membranes under differing conditions of

ion concentration, ion type and temperature.

To compare d.c conductivity measurements versus a.c. conductivity measurements

and determine which method is more suited to the measurement of the conductivity of

polymer electrol yte membranes

EXPERIMENTAL DETAILS

HOT PRESS DESIGN AND CONSTRUCTION

The testing of pressing parameters for the fabrication of membrane electrode

assemblies was carried out using a hot press that was designed to operate at temperatures

between 120 - 180°C and pressures up to 13.8 Mpa (2000 psi). These temperature and

pressure ranges were selected because other workea have fabricated MEAs under similar

conditions. (17-20)

The press. show in figure 8 (page 19), was designed so that the applied pressure

could be accurately measured ( 2 20 psi). The electrodes that were used in the testing of hot

pressing conditions were 35 mm in diameter. To accurately apply the required pressure. the

pressing platens (figures 6 and 7) were designed so that the pressure was applied to an area

with a diameter of 35 mm. This was achieved by machining the bonom platen to create a 35

mm diarneter raised section in the centre. The upper platen was attached to an Enerpac RC 55

(Appendix 5, section 5 ) hydraulic piston, rated at 2.27 tonnes (5 US tons) with a 12.7 cm (5

in) stroke; the bottom platen was fixed. The platens were made From mild steel. The raised

section of the bonom platen was covered with a stainless steel cap and the surface of the

upper platen was covered with a stainless steel plate to prevent contamination of the samples.

The piston and platens were mounted into an Enerpac model A-205 C clamp, with a capacity

of 5 US tons(Appendix 5. section S ) , that was secured to a base. The platens were insulated

from the C clamp and the piston using Marinite board (Appendix 5. section 5) in order to

prevent the clamp h m being heated and to prevent thermal degradation of the hydraulic fluid

in the piston. The piston was activated using an Enerpac model P-39 hydraulic hand pump

that was also secured to the base. Heating was achieved using four Omega CSS - 20 150,

50 W cartridge heaters; two in each platen. Temperature measurement and control were

achieved using an Omega KTSS - 3 16G - 2 thermocouple and an Omega CN76000 PID duai

output temperature controller from Omega (Appendix 5, section 5).

U ~ p e r Platen: Front View

Piston uttachment ,-> T? ri ttaching plate ------3 (mi fd s ee f)

Therrnocouple port 0 0 P O i l '1L i

1

Stuinfas steel plate + f

0.5 cm 0.97cm

U b e r daren: TOD view

Figure 6: Front and top views of upper platen

Lower duten: Front view

Thermocouple port 0 0 0 0 0

Catridgz hzatzr port 1.5 cm

(mild steel) 2.53 cm

1 .O cm

Base A ttachmenr

Lower dgten: TOD view

Figure 7: Front and top i&us of io wer p faten

MEA FABRICATION AND TESTXNG

The electrodes that were used in the hot pressing tests were fabiicated according to the

procedure outlined by Hirai (Appendix 5, section 4). '"' Nafion Q117 membranes (Appendix

5. section 5) were processed by tùst boiling in 250 mL of 5% H202 for 1 hour. The

membranes then were boiled three times in 250 mL deionized water (MiIlipore, 18 MR.cm)

for 30 minutes eacn ume. Finaily, the membranes were acidified by boiiing in 250 mL of 1 .O

M H2SO4 for 30 minutes. Processed membranes were stored in deionized water. '"."' Hot pressing tests were canied out using various combinations of temperature.

pressure and time. Temperatures of 125, 140, 1 55 and 1 70 O C : pressures of 4.1.6.9. and 1 1

MPa (600. 1000. and 1600 psi) and times of 30,60 and 90 seconds were used. To pertkrm the

tests, membrane and electrode were sandwiched between two Teflon disks (35 mm diameter)

and the sandwich was inserted between the platens and allowed to reach the appropriate

temperature. Once the Teflon-membrane-electrode sandwich reached the set temperature. it

was pressed for the required time at the required pressure. Afier pressing, the sandwich was

allowed to cool, the Teflon plates were removed and the integrity of the resulting MEA

(electrode + membrane) was qualitatively tested by attempting manually to separate the

membrane from the electrode. The relative degree of difficulty of separation was used as the

measure of the quality of bonding for that particular combination of temperature, pressure and

tirne.

MEMBRANE CONDUCTMTY TESTTNG

The conductivity of Nafilon@ membranes was investigated by first preparing the

membranes as outlined above. For tests involving single membranes. the membrane was

placed into an electrochemical ce11 in which the luggin probes could be slid to different

distances h m the membrane (figure 9).

Once the membrane was inserted into the cell and the cell was filled with the test

electrolyte (approximately 45 mL), a constant direct cment of 4.000 rnA ( f 0.00 1 rnA) was

applied to the current carrying electrodes (platinum electrodes) using an EG&G model 175

potentiostat/galvanostat. The resulting IR drop across the membrane was measured using a

Hewlen Packard model 34401A digital multimeter that was comected to the ce11 via two

saturated caiornel rlect.rodes that wrre placrd into sliding luggin capiiiaries. Mrasuremrnts

were taken with the luggin tips separated by 1,2,3,4,5,6.7. 8 and 8.7 cm (in addition to the

membrane thickness). These IR drop measurernents were taken five times per m. Four runs

were taken per electrolyte used. The electrolytes used were 0.0 1 M, 0.05 M, 0.1 M, 0.5 M, 1 .O

M and 0.6 M KCl. Eight tests were cmied out on single membranes (processed) using

0.6 M KC1. These expenments were perfonned at 25OC (k 02°C) using a Julabo C circulation

pump with a Precision Scientific constant temperature water bath. Expenments at different

temperatures also were performed using single (processed) membranes in both 1 .O M H2S04

(3. 12.25 and 35°C) and 0.6 M KCI (2. 12.25 and 35OC). In addition, conductivity tests were

carried out on membranes that were bonded together by hot pressing. Tests were performed as

described above on two and three-membrane composites that were pressed at 170°C. 1 1 MPa

and 90 S. The pressing process was the same as described for the bonding tests. Conductivity

measurements also were made on a single membrane that was hot pressed (a single membrane

composite) under the conditions just descnbed and a single membrane that was heated,

without pressing, to 170°C for 4.5 minutes. Measurements were taken at H2S04

concentrations of 1.0 M. 0.5 M. 0.05 M and 0.0 1 M in the same mamer as before. For al1 the

membrane combinations, the membrane thickness was rnea~u~ed using a Moore and Wright

micrometer and recorded. For these measuements, the membranes were soaked in deionized

water and then the surface was bloned dry. The membrane thickness was taken as an average

of nine thickness measurements per membrane. The experimental setup is show in figure 1 1 .

Sample calculations are s h o w in appendix 1.

Measured IR drop across membrane

DIGITAL MULTIMETER

C A

+ - POTENTIOSTATI GALVANOSTAT

;

A

Figure I I: Schemaric of experùnen fa1 setup for d c conductivi@ measuremen&.

Conductivity measurements also were carried out using an ac. method in which the

membranes first were cleaned as previously descnbed, then cut into 1 .O cm x 2.5 cm strips

and placed into the appropriate solution. The solutions used were the same a s those for the

d.c. tests. The mips were then placed into a clamp ce11 (figure 12). The pressure applied to the

membrane when it was clamped was fixed as described by irai!'^' After the membranes

were securely clamped into the cell. the ce11 was c o ~ e c t e d to a Radiometer mode1 CDM83

conductivi ty meter, and conduc tivïty measurements taken.

Plutic stopper

Stainless steel screw

Lucite clamp

Stainless steel cl@ pin attached to stainless

Figure 12. Front vimv of clamp ceil used for ac conductivity measuremenfs

steel contact

i I

Lucire clamp body

Stainless steel pad

I & I .

Lucire l+----4

15 mm base

Figure 13. Cross seciional vlew of the contact area of the clamp in figure 12.

-

The cell constant for the clamp cell was determined as previously described using equation 2.

D.C. conductivity measurements of a Naf50n@ membrane in pure water also were

carried out. These measurements were made using the sliding cell with the luggin capillaries

removed. Platinum mesh (size 30 mesh) current carrying/measurement electrodes with an area

of 1.0 cm' were hot pressed into each side of the membrane at 140°C and 6.9MPa for 90

seconds. The membrane was then placed into the slidmg cell and the electrodes were

connected to the EG&G model 175 potentiostat/galvanostat and to the Hewlen Packard model

3440 1 A digital multirneter. The current was switched on, the IR drop across the membrane

was immediately recorded and the current was switched off. This was repeated several times.

The physical characteristics of the single membranes were evaluated by determining

the mass and dimensions-length, width and thickness-of three different membranes during

the various stages of processing. Measurements were taken from as-received membranes.

after boiling in 5% v/v H202, after boiling in deionized water, after boiling in H2S04. after

storage in a hydrostat for 24 hours, after drying at 125OC for 1 hour and after rehydration.

Membrane water content (per unit of dry mass) also was investigated. This was achieved by

measuring the mass of the membranes in a fully hydrated state (after they had been immersed

in deionized water and then had the surfaces patted dry). The membranes were then dried in

an oven at 125°C for I hour. Immediately after drying, the membranes were placed

(individually) into a petri dish. covered and weighed. The mass of the membrane was

measured over time (as it absorbs atmospheric moisture) and the mass at time = 0 was

determined by extrapolation. The water content was then calculated using this value.

Membrane ion exchange capacity was determined for single unpressed. single pressed

and heat treated membranes. This was achieved by fim stirring the membrane in 250 mL of

2.0 M NaCl while sparging nitrogen gas through the solution for 1 hour. The resulting

solution then was titrated with standardized 0.05M NaOH to an end point, Mer titraiion each

membrane was processed (cleaned and put into the H' ion form) as previously described. The

procedure was carried out 3 times for each membrane type. Mer d l titrations were carried

out, membrane dry mass was then determined by the procedure described in the previous

P ~ W P P ~ .

RESULTS AND DISCUSSION

MEA FABRICATION AND TESTING RESULTS

Testing of the hot pressing parameters revealed that regardless of the pressure and

thne combinations, pressing at low temperatures (below 155°C) was ineffective. Bonding that

took place at 155OC showed better adhesion than at lower temperatures. The highest quality of

bonding was found in MEAs that were hot pressed at the highest temperature tested (1 70°C).

in general, the adhesion between the membrane and the electrode improved as the hot

pressing temperature increased (see Table 1 .).

At low temperatures (below 140°C), melting of the membrane does not occur because

the t,, has not k e n reached; therefore at temperatures below 140°C, thermal bonding of the

membrane to the electrode does not take place. '2" Poor bonding was observed in MEAs that

were hot pressed between 140°C and 155°C (at al1 time and pressure settings tested); these

temperatures were still not high enough to melt the membrane to the degree required for good

adhesion. It was found that at 140°C adhesion of the membrane to the electrode was still poor

(the membrane was easily peeled From the electrode), while at l S ° C the adhesion was much

better, but separation of the membrane and electrode was still easily achieved. Hot pressing at

1 70°C for 90 seconds, at dl pressures tested showed excellent bonding of the membrane to

the electrode in that the resulting MEA had to be destroyed in order to achieve separation. At

the parameter combination of 170°C, 1 i Mpa (1600 psi) and 90 seconds it was found that the

MEA produced by the hot pressing procedure was warped. As the pressing pressure was

reduced the degree of warping also was reduced. Hot pressing at 1 70°C and 1 1 MPa for 60

seconds also produced MEAs that showed excellent bonding between membrane and

electrode (i.e., the membrane could not be separated fiom the electrode). At lower pressures

(same tirne and temperature settings), although good adhesion was achieved, it was still

possible to separate the membrane from the electrode. At lower time and pressure settings

(same temperature), good adhesion was achieved. however the membrane could be separated

fiom the eIectrode.

NUMBER PRESSURE 1 TIME f RESULTSKOMMENTS

Easily peeled. Poor adhesion 600 1 4.1 1 30 1 apparent.

600 / 4.1

600 1 4.1

1600 / 11

Easily peeled. However. adhesion was better.

60

1600 1 11

Easily peeled. Poor adhesion apparent.

90

90

Easily peeled. Poor adhesion apparent.

Easily peeled. Poor adhesion apparent,

90

600 1 4.1

Peeled intact, Adhesion appeared to be good.

;

Easily peeled. Poor adhesion apparent

600 / 4.1

600 / 4-1

Peeled intact. Adhesion appeared to be good.

30 Peeled intact. Adhesion appeared to be good.

60

90

Peeled intact. Adhesion appeared to be good.

Peeled intact. Adhesion appeared to be good.

1600 / 1 1

Table 1: Resuh of ME4 fabrication tes&

90

60

Did not peel. Adhesion appeared to be good. MEA was warped.

Did not peel. Adhesion appeared to be good.

D.C. CONDUCTIVITY RESULTS

D.C. Measurement Results

The conductivity of the membrane was measured in varying acid concentrations. For

ench membrane confîguration, a graph of the log of conductivity versus the log of

concenmtion was piotted and a ieast squares linear regession rnethod was appiied to grncratr

an equation describing the graph (figures 15 - 19). The data are shown in table 2. Figure 14

shows plots of the log conductivity venus acid concentration on a linear scale.

Concentration (M)

Figure 14. Log conductivity vs H-80, concentrarion for ail membranes. Seriesi, single processed memôrane; Series 2, singie ntembrane heated to I T O T ; Series3, single membrane composite; Series 4, two membrane composite; Seties 5, rhree membrane composite

CONC'N and CONDUCTIVITY

r

MEMBRANE CONDUCTIVITY (~.m-')

PROCESSED MEMBRANE

Table 2: D.C. conductivity data ut 2S°C. Mentbrune corngosires were hot pressed a2 I 70°C and I I MPa for 90 S.

THREE HISOJ

Log Concentration (M)

SINGLE 1 MEMBRANE 1 SINGLE 1 TWO HEATED TO

1 70°C

- -- -- - - - - - - . - - - . . . - - - - - -- - - -- - - -

F i g m 15. Log &SU4 concentration vs log conductivtty for a srngle procpssed membrune.

MEMBRANE COMPOS1TE

MEMBRANE COMPOSITE

MEMBRANE COMPOSITE

-2 -1.5 - 1 -0.5

Log Concentration (M)

Figure I î i Log H _ 8 0 4 concentration vs log conductivity for a sùtgle membrane heat-treated at I 70°C.

-7 -1.5 - 1 -0.5 O

Log Concentration (M)

-3 - -1.5 - 1 -0.5

Log Concentration (M)

Figure 18. Log H.SO, concentrafion us log conducfivity for rwo membrane compos.lfe*

-7 - -1.5 - 1 -0.5

Log Concentration (M) - - - -- - .

Figure 19. Log H s 0 4 concemration vs log conducrivity for rhree membrane composife

From the graphs, it can be seen that, as expected, as the concentration of acid

decreases, the conductivity also decreases. Free acid is held within the ionic clustea (the

intemal solution); acid produced by the dissociation of the H' ion from the ion exchange site.

The decrease in the conductivity is a reflection of the increasing dificulty in transporting the

ions fiom the extemal acid soiution in contact w i h the membrane that is Iess concentrateci

than the intemal (membrane) acid concentration. Therefore because there are fewer H' ions

available for transport (from the extemal solution), ionic conduction becomes more difficult.

It was expected that when two membranes were bonded together, there would be an

interfacial (contact) resistance between the two membranes, impeding the flow of ions across

the boundary. The possibility of a contact resistance arising beween the hot pressed

membranes is of concem because this would negatively affect the IR characteristics of an

operational fuel cell. The IR measurement results in Table 5 show that, for a given acid

concentration (especially at low concentrations), as the thickness of the pressed membrane

R composites increased the resistance per unit thickness ( -) actually decreased: i.e.. the

2

R conductivity increased. Also, there was a general trend for - to decrease and approach

I

similar values as the acid concentration increased. This suggests that there is no interfacial

R resistance between the hot pressed membranes. If an interfacial resistance existe4 then -

i

R would be expected to increase with increasing thickness. The obsewed decrease in - cannot

I

be accowited for at this tirne.

Figure 14 shows that as the acid concentration increases, the value of the

conductivity of the various membrane configurations converges to a value of approximately

33

5.9 s.6'. This is especially evident at the acid concentrations of 0.5 M and 1 .O M where it

can be seen that the conductivity values for d of the membrane configurations are generally

similar. As the acid concentrahon decreases, the conductivity of each membrane configuration

diverges with the untreated membrane showing the lowest conductivity; followed by the

single-, two- and three-membrane composites. The heat-treated membrane showed the highest

conductivity. Tne data show that for a given acid concentration, the measured r:sis(ance

increases as the nurnber of membranes pressed together (i.e., thickness) increased (table 9.

appendix 1). While the increase in the resistance was expected, it was thought that the

conductivity would be constant for al1 membrane cor@urations.

At the higher acid concentrations the number of H' ions available for transport is large

and therefore at such concentrations the quantity of H' ions is high enough to possibly negate

the effects of other phenornena that May alter the conductivity of the various membrane

configurations. The quantity of H' ions available for transport would be so large that the

resulting conductivity of the membrane is more a reflection of the availability of H' ions than

it is a reflection of the actuai inherent conductivity of the membrane.

Looking at Fig. 20. it can be seen (more clearly) that at low acid concentrations the

conductivity of the untreated (series 1) and the single pressed membranes (series 3) are both

very similar and they are also distinctly lower than the other membranes. ?Xe lower

conductivity of the single, thimer membranes could be attributed to a stagnant layer of

solution at the membrane/solution interface that adds an additional resistance to ion flow. This

wodd result in the resistance of dl of the membranes being elevated by a constant value. It

would also result in the conductivity of the thinner membranes appearing to be lower than the

thicker membranes because the resistance due to the barrier is a greater portion of the totai

resistance in the thinner membranes thm the thicker membranes: this would be reflected as a

lower conductivity for the thinner membranes. However, this is contradicted by the fact that

the calculated limiting current density for this set up is 998 rn~ .cm-~ (Appendix 5) whereas

the current density of the ce11 is only 1.6 m~.cm**. Also the membrane heat-treated to 1 70°C

shows the highest conductivity of al1 the membranes tested and is aiso the thinnest membrane

tested. If the above scenario was correct, then the heat-treated membrane should have a lower

conductivity. It is possible that the heat-treating process has a slightly different effect on the

membrane structure than the hot pressing process, which results in an elevated conductivity.

Concentration (M)

Figure 20. Log conductivity (calculated) vs H-80, concentrarion (up to O. IM) for all membranes. Series l , unpressed m d r a ~ e ; Seria 2, single membrane heored to 2 70°C; Series-t, single membrane composire; Series 4, two membrane composite; Series 5, tihree membrane cornpusile

The results also show that the conductivity for the single, pressed membrane was

higher (even if by ody a small margin) than the untreated membrane. It would therefore seem

that hot pressing the membranes affects them in such a way as to increase the conductivity.

During the hot pressing process, a reordering of the structure of the polyrner takes

place!29' The membranes were hot pressed at 170°C, which is well above the glass transition

temperature of 140°C (the minimum temperature at which melhg will rake place) for

Nafion@. Hot pressing the membranes above the glass transition temperature may produce

morphological changes in the structure of the polymer that result in the membrane being more

conductive. These changes may be similar to those that occur when a Nafion0 film that has

k e n cast from a solution at room temperature (a recast Nafion@ membrane) is thermally

treated to produce a "solution cast" membrane. Using wide angle X-ray scattering and small

angle X-ray scattering studies. Gebel. Aldebert and Pineri '"' have shown that thrre are

morphological differences between recast, solution cast and as-received Nafion@ membranes.

They proposed that *when a recast membrane is thermally annealed (heat-treated), there is an

increase in the size of the lamellar crystallites, an improvement in the intemal order and a

long ranged structural order is developed; al1 of which are partly due to the thermal

anneal h g ."

Several studies have shown that membrane conductivity is directly related to the

quantity of water thai is held within its intemal structure and that the higher the water content

of the membrane. the more conductive the membrane becomes, ( L 5.27.30) To veri& this, the

water content of each membrane was determined. The resdts of the water content studies are

shown in table 3.

(g H201g dry membrane) IN 1.0 M H2S04 IN 0.01 M HzSOI (~.m*') (S. m*')

I

Single, untreated membrane,

1 Single membrane 1 I composite I

L

Membrane heated to 1 70°C.

Two membrane composite

0.37

Table 3. Membrane water content results for Nafion@ 11 7. Also shown Ls a cornparison of conductivity values at given membrame water content values

I 5 -44

0.69 0.20

The results show that the membrane composites that have been heated or hot pressed

show significantly lower water contents (approximately 3 8 2% lower) than the untreated

membrane. The results also show that the water content of the heated membrane composite is

as Iow as the water content as the membrane composites that were hot pressed.

As water uptake of the membrane proceeds, and the water content of the membrane

increases, the polymer side chah deforms in order to accommodate the increase in cluster

volume that is associated with increasing water ~ontent.''~' Gierke et al '15' have demonstnited

that ionic clusters increase Ui size in propottion to the quantity of water that is being absorbed.

The increase in cluster size deforms the polymer chah network. In our case, it was originaily

expected that the combined effects of temperature (above the g las transition temperature) and

pressure during the hot pressing process would result in the membrane undergoing structural

changes similar to those just described and that these changes wodd restrict the deformation

of the polymer chahs (due to the increased long range order and larger larnellar crystallites).

This in tum should ümit the amount of water that the membrane can hold. Consequently, one

37

0.23

6.94

1

5.25 Three membrane

composite 0.53 0 3 3

would expect a lower conductivity for the pressed composites (one. two and three membrane

configurations) versus the untreated membrane, rather than the higher conductivity that was

actually observed (see Table 3).

It is possible that while some of the morphologicai changes that occur during the hot

pressing process ultimately have an effect that should lower the conductivity; other changes

may serve to enhance it. As previousiy mentioncrd, it wouid appear that the hot pressing and

heat-treating processes impose a long ranged order on the structure of the membrane and

increase the size of the lamellar crystallites. It is possible that these changes render the pore

volume smaller and more compact so the water that is held within the membrane is held

within a smaller volume. Also, this would increase the concentration of the ion exchange

sites. resulting in a higher measured conductivity because less water would be needed for

conduction to take place. This could partially explain the greater conductivity of the heat-

treated and hot pressed membranes. The larger conductivity of the heat-treated membrane (as

compared to the hot pressed membranes) could be due to the lack of applied pressure during

the heat treatment that may resuit in morphological changes that are slightly different to those

that may have occurred in the hot pressed membranes.

It was also thought that the hot pressing and heating processes might have affected the

ion exchange capacity (the number of ion exchange sites per gram of dry membrane) of the

membrane and therefore the conductivity. Membrane titration results indicate no affect on the

ion exchange capacity by these processes. The literature value for the ion exchange capacity

of Nafion@ 1 17 in the Ht ion fom is given as 0.91 meq.g-'!33' Membrane titration results are

given in table 4:

MEMBRANE ION EXCHANCE CONFlGUIZATION CAPACITY

1 Heated to 1 X ° C for 1 hour I 0.904 I Heated to 170°C for 4.5

min.

Table 4. Membrane ritration results for Nufion@ I I 7.

0.895

Hot pressed at 170°C. 1600 psi for 90 sec.

Cornpat-hon of Results with Other Studies

0.905

D.C. methods are not typically used to determine membrane conductivity, the vast

rnajority of studies using a.c. impedance methods primarily because of the ease of

measurernent. However, there are a few studies that have measured membrane conductivity

using d.c. methods. Table 5 sumrnarizes some of the available d.c. conductivity data for

Nafion@ membranes.

MEMBRANE TYPE SOURCE OF DATA CONDITIONS I I I 1 ELECTROLYTE 1 CONDUCTIVITY 1

Junginger & Stmck, Int. J. Hydrogen

Energy, Vol 7, No. 4, pp 33 1 - 340, 1982%

Nafion@ 1 10 (EW, 1100)

Untreated membrane. Temperature, 80°C

Thickness, 0.0254 cm

Junginger & Stntck, Int. J. Hydrogen Nafion@ 120

(EW 1300) Untreared membrane, Temperam, 80°C

ïhickness, 0.0254 cm Energy, Vol 7, No. 4, pp 33 1 - 340, 1982:

lunginger & Stmck [nt, J. Hydrogen

Energy, Vol 7, No. 4, pp 33 1 - 340, 1982:

Nafion@ 125 (EW 1200)

Untreated membrane. Temperature. 25°C

Thickness. 0.0 137 cm

Nafion@ 1 17 (EW 1100)

Untreated membrane. Temperature, 2S°C

Thickness. 0.02 16 cm

This thesis

This thesis Nafion@ 1 17 (EW 1 100)

Untreated membrane. Temperature, 25°C

Thickness, 0.02 16 cm

0.6M KCI

The E. 1. DuPont de Nemours & Company

1nc.t

Nation@ 1 17 (EW 1 100)

Untreated membrane. Temperature, =OC* Thickness, unknown

O.6M KCI

*Tempt'rarure specified as "room temperature" in lirerature, Therefore assumed to be 22°C. $ See reference 3 1

at 20°C f See refirence 33

Table S. D.C. conducfivity daîa summary.

The similarîty of the results s h o w in Table 5 clearly show that the d.c. method that

was employed in t a h g conductivity measurements for this thesis is a valid one. It should be

noted that while there is agreement between the values Qr the Nafion@ 125 and N&on@ 1 17

membranes, the Nafion@ 125 membrane is slightly less conductive than the Nafion@ 1 17 (it

has a higher equivaient weight and as such there are fewer ion exchange sites per unit

volume). However, it was tested in an acid solution that is slightly more conductive than the

one used in this thesis. It can also bee seen that the conductivity values for Nafion@ ( 1 100

EW) in 0.6 M KCl are in very close agreement.

D.C. Conductivitv of Nafion@ in Pure (Deionized) Water

The d.c. conductivity of untreated Nafion@ in pure water also was iavestigated. It was

found that the conductivity values produced by these measurements were extremely low, the

average value being 2.23 m~.m-' . which was however, greater than the value of 0.078 m~.rn-' .

caiculated (Appendix 1. section 4) for the conductivity of an untreated Nafion@ membrane

with an H' ion concentration of IO-' (equivalent to that of pure water). The large discrepancy

between these values can be attributed to the difficulty in obtaining instantaneous. stable

voltage readings due to rapidly increasing overpotentials at the electrode surfaces and the

scatter in the data used to produce the caiculated value.

A.C. vs D.C. METHODS

Membrane conduc tivity also was measured using the a.c. method previously

described. A cornparison of the a.c. and d.c. values is given in Table 6.

ELECTROLYTE

Table 6: Compacison of ac und d c, condrrctivity data

There was a senous discrepancy between the resdts of the ac. method and the d.c.

method. The conductivity values for Nafion@ in H2S04 determined using the ac. method

were up to an order of magnitude higher than those obtained using the d-c. method. The H'

ion conductivity for Nafion@ in pure water was rneasured by ac. impedance to be 9.5 ~.m- ' ,

CONDUCTIVlTY (S. m" )

10.3 1

9.58

9.62

8.9

8.8

0.8 f

9.54

1 .O M HISOI

0.5 M HzSOr

O. 1 M H2S04

0.05 M H2SOI

0.0 1 M HtSOj

0.6 M KCI

Pure water

CONDUCTlVlTY (~.m")

5.44

4.88

t .3

I .O 1

0.23

1 .O9

0.00333

whereas the d.c. conductivity at an acid concentration of 0.001 M (a value taken to represent

an acid concentration of O M) is 0.05 16 s.rnS'. Similarly, the conductivities of Nafion@

membranes in 0.6 M KCI obtained by a.c. impedance were 28.9% Iower than those obtained

by the d.c. method. The literature value for the resistivity of 1 100EW Nafion@ (the same type

of polymer used in these experiments) Ui 0.6M KCl at 'room temperature" given by the

DuPont Company (rnanufactureo of Nafion&) is 100 ohm.cm.!"! The resistivity determined

using the d.c. method at 25OC was 96.2 ohm.cm (3.8% smaller than the given value).

Resistivity measurements were also made at different temperatures (Figure. 20). The resulting

curve of resistivity venus temperature showed that if room temperature is assumed to be

22°C. then, using the d.c. method of these experiments. the resistivity of the membrane would

be 100 ohrn.cm. Therefore, the d.c. method is accurate for determining the conductivity of

Nafion@ membranes.

The apparent discrepancies can be explained by the fact that the acid concentration in

the membrane is not zero becaw the ion exchange sites are protonated. Therefore

equilibrium exists between the H' ions attached to the ion exchange sites and the water held

within the membrane structure (essentially creating an acid solution within the membrane).

The concentration of ion exchange sites in Nafion@ is 1 .O5 M (Appendix 5. section 4).

Therefore the concentration of the acid soiution in the membrane could be as high as 1 .O5 M,

which is dependent upon the degree of dissociation of K ions fiom the ion exchange sites. It

is well known that Nafion@ is a strong a~id'~'' and as such it would expected that the W ions

be fully dissociated fiom the ion exchange sites. A.C. impedance would therefore be

measuring the conductivity of an acid solution (at some unknown concentration. possibl y

around 1.0 M) in the Nafion@ membrane and as such the conductivity would be similar to

that of the d.c. conductivity of Nafion in an acid solution of the same concentration. This

could account for a large part of the discrepancy between the conductivity values measured by

ac. and d.c. methods.

During êc. impedance tests the polarity of the current that is applied to the membrane

is constantly changing at a high rate. Therefore it is unlikely that the steady state ionic

conduction through the membrane that takes place during the operation of a fuel ce11 will be

achkved. h tead , is likely that the rapid changes in poiarity couid resuit in the rnovement of

ions back and forth within a cluster or between a small number of clusters. If this were the

case, then the resistance would be very small because the ions do not have to negotiate the

cluster network through the entire thickness of the membrane. The resistance to ionic flow

would be smailer because of the shorter distance that the ions travel; therefore the

conductivity produced by such measurements will be higher than the mie steady state value.

The changes in polarity are govemed by the frequency of the applied current. Therefore it is

more likely to occur when measurements are made at higher frequencies. In their 1993 paper,

Fontanella, McLin, Winteagill, Calame and ~reenbaurn'~'' state that unspecified frequency

effects have been observed when the applied frequency was above 1MHz and they affect the

bulk conductivity. These effects decrease as the fiequency is lowered.

This behaviour might exert a great effect on the conduction of K ion in Ndon. It is

thought the conduction of the H' ion through Nafion is achieved via a Grotthus conduction

mechanisrn; (*'' therefore, the conductivity of H* ion is higher than that of K' ion. The polarity

changes that occur when using ac . impedance produce an effect in which the K ion is

continuously shifted back and forth between adjacent ion exchange sites. Thus, the resulting

resistance would be smaller than the acnial resistance because. as postulated above. the ion

does not actually travel the entire thickness of the membrane.

Using a-c. impedance, the conductivity of Nafion in 0.6 M KCI was found to be lower

than that determined using the d.c. method. This is in contradiction to the generally expected

trend of the ac. irnpedance method producing a conductivity value higher than that produced

by the d.c. method. This may be due to the transport characteristics of the K' ion. It is

possible that there is an added resistance to response of the K' to the polarity changes that

occur during ac. impedance.

A.C. impedance methods have been used extensively by others '"" 'j.". 30' to study

the conductivity of Nafion membranes under the varying conditions of humidity (water

content) and temperature. Typically the response data are automaticaily collected. and plotted

in a variety of ways such as Bode, Cole-Cole. Arrhenius or Nyquist plots. These are then

analyzed to give a value for the conductivity. In their impedance study of NafionB.

Fontanella, Wintersgill etal '25' transformed the data to a complex dielectric constant that was

rnathematically transformed to a conductivity value. It mut be noted that they emphasized.

"This represented an apparent conductivity that was calculated directly fiom the equivaient

paralle1 resistance of the sample (real part of the impedance)". Therefore the resistance of the

sample is derived h m the interpretation of complex equations and is not duectly measured.

Hence, it is possible that because the resistance is not directly measured, some error is

introduced into the calcdation of the resistance. This is possibly due to the inability of the

mode1 equations used in the mathematical analysis to fully describe the behaviour of the ions

during transport through the membrane. A summary of the data is given in table 7.

and DesMarteau; J. Electrochem. Soc., Nafion@ 1 17

Vol 145, No. 1 ,

SOURCE OF DATA

1 Sone, Ekdunge,and 1

MEMBRANE TYPE

~imonsson; J. Elecû-ochem. Soc.,

Vol l43,No. 4, P 1254-1259,1996

Fontanella, Wintengili McLin,Calarne and Greenbaum.; Solid

State Ionics, 66, p 1-4, 1993

Anantaraman and Gardner,

J, Electroanal. Chem., 414, p 115-120,1996

This Thesis

* Rssumed to be room temperature ' Free H$04 msumed to be absent

EXPERIMENTAL CONDITIONS '

Temperame, =OC* Relative Humidity,

1 OOOh. Water vapour partial pressure,

2x 1 o4 ~a

Temperature, 30aC Relative Humidity,

1 00%

Temperature, T C Relative Humidity,

100%

Temperature, 22T* Relative Humidity,

100%

Temperafure, 22OC Membrane saturated

Tàble 7: Sumntav of ac condudivlfy daîa for Naflotta 11 7.

METHOD

- --

CONDUCTIVITY (S. m")

Four point probe method.

Four point probe 1 1.0 method

Four point probe method

Coaxial probe method

Two point probe l 9.5

It shouid be noted that while there is reasonable agreement between our values and

those obtained by other workers, the equipment set up used for our experirnents was quite

different fiom those of the other workers.

EFFECT OF TEMPERATURE ON MEMBRANE CONDUCTIVITY

The conductivity of Nafion at varying temperatures in both 1 .O M H2S04 and

0.6 M KCl was investigated using the d.c. method. The numencal results are s h o w below, in

table 6 and are plotted in figures 22 and 23.

- - . - -. -

Table 8. Conductivity data for Nafion@ in 1.OM H.80, and 0.6M KCI at varying tpniperamres.

TEMPERATURE ( O C )

As expected, the conductivity increases with temperature. Figures 23 and 24 are plots

of log conductivity vernis inverse temperame. The slopes of the plots are related to the

activation energies for conduction.

CONDUCTIVITY IN 1.OM HzSOJ (s.m-')

CONDUCTIVITY IN 0.6M KCI

(s.m-')

Figure t l ConducWty vs temperature, Seriesi, conducrivity of I.OM H-SO,; Series 2, conductivity of NafiondB 11 7 in 1.OM H.S&

Temperature ( OC)

Figure 23. Log conductiv& vs inverse tempernrre. Seriesl, 1.0M HHSOJ; Series 2, Nafion@ 2 1 7 in 2.OM HfiSOb

Figure 24. Log conductivity vs Uiverse temperature for Nafion@ I I 7 in 0.6M KCI

49

The activation energies calculated from the above graphs are &en in table 8:

IONK CONDUCTION MEDIUM

ACTIVATION ENERGY (k.J.rnor1)

0.6 M KCI

Nafion@ 1 17 membrane in 0.6 M KCI

13.6

Nafion@ 1 17 membrane in 1 .O M H,S04

Table 9. Activation energy d m

14.9

The activation energy values suggest that as expected, the conduction of ions through

Nafion@ 1 17 is a physical process. It was expected that because the conductivity of the K ion

was larger than that for K' ion due to it being conducted by the Grotthus conduction

mechanism. the activation energy of ion conduction would be smaller than that for K' ion.

However, the results show that the activation energy for the conduction of H' ion in Nafion@

is 17.4% higher than the K+ ion conduction activation energy. Also the activation energy for

ionic conduction in aqueous KCI should be lower than that for the conduction of Ii' ions

through Nafion@ 1 17. These discrepancies could be attributed to the scatter in the data, which

introduces some error in the regression of the data.

CONCLUSIONS

In terms of the mechanical integrity and strength of the bond. the best hot pressing conditions were 1 70°C, 1 1 MPa for 90 seconds. However good bonding was observed at and above the temperature of 155°C.

The value produced by d.c. measurement of the conductivity of Nafion@ in pure water (2.23 m~.rn-') is unreliable unless instantaneous voltage measurements are taken.

At high acid concentrations, the acid concentration becomes the most important factor in detemiining the value of Nafion@ conductivity.

The Iargest improvement in conductivity was seen in the heat-treated membrane. It is possible that this improvement in the conductivity is due to morphological changes that take place when the membrane is heated. Surface phenornena also may affect the conduc tivi ty .

Water uptake measurements suggest that it is the heating of the membrane (above its glass transition temperature) and not the pressing, that affect the membrane's ability to absorb water.

The hot pressing of the membranes does not appear to introduce an interfacial resistance between the membranes.

The d.c. method is an accurate technique for the determination of the conductivity of Na£ion@ 11 7 membranes. Conductivity measurements made using ac. impedance are subject to some erron that are not encountered when using d.c. methods. However both methods are useful in conductivity measurements.

As expected the conductivity of NafionO 1 17 in acid and KCI increases as the temperature increases.

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A. Eisenberg, "Clusterhg of Ions in Organic Polymers. A Theoretical Approach", Macromolecules, 3 (2). 147 - 1 54. (1 970).

T. D. Gierke, G. E. Munn and F. C. Wilson, "Morphology of Perfluorosulfonated Membrane Products: Wide-Angle and Small-Angle X-ray Studies", Amerïcan Chernical Society Symposium Senes on Perfluorinated Ionorner Membranes.283 -

(1 5) M. R. Tant, K. A. Mauritz and G. L. Wilkes, " Ionorners: Synthesis. Structure, Properties and Applications", Chap. 3, 1 O4 - 1 13, Blackie Academic & Professional (1997).

(1 6) T. Hashimoto, M.Fujimura and K. Kawai, "Structure of Sulfonated and Carboxylated Perfuorinated Ionomer Membranes", Arnerican Chernical Society Symposium Series on Perfiuorinated Ionomer Membranes,2 1 7 - 248, ( 1982).

(17) 2. Poltarzewski, P. Staiti, V. Alderucci, W. Wieczorek and N. Giordano, "Nafion Distribution in Gas Dimision Eiectrodes for Solid-Polymer- Electrolyte-Fuel-Cd Applications", J. Electrochem. Soc.. 139 (3), 761 - 765, (1992).

(18) E. A. Ticianelli, C. R. Derouin and S. Srinivasan, " Localization of Platinum in Low Cataiyst Loading Electrodes to Aciain High Power Densities in SPE Fuel Cells". J. Electroanal. Chem, 251,275 - 295, (1988).

(19) E. A. Ticianelli, C. R. Derouin, A. Redondo and S. Srinivasan "Methods to Advance Technology of Proton Exchange Membrane Fuel Cells". J. Electrochem. Soc.. 1 35 (9), 2209 - 22 14, (1 988).

(20) E. A. Ticianelli. J. G. Berry and S. Srinivasan, "Dependence of Performance of Solid Polymer Electrolyte Fuel Cells with Low Platinurn Loading on Morphologie

Characteristics of the Electrodes", J. Appl. Electrochemistry, 21.597 - 605. ( 1997).

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(22) J. Sumner, S. Creager, M. Ma and D. DesMarteau. " Proton Conductivity in Nafion 1 17 and in a Novel Bis[(perfluoroalkyl)sulfonyl]imide Ionomer Membrane". J. Electrochem. Soc, 145 ( 1 ), 107 - 1 i 0, (1 998).

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APPENDIX 1: SECTION 1. D.C. CONDUCTIVlTY DATA

DATA FOR SINGLE, UNPRESSED MEMBRANE IN 1.0 M Hz& AT 35OC.

'Th~ckncss

(cm) 00218

dclla I. (cnl)

lo218 2 02111

3 0218

4 0218 5 0218

60218 7 0218

80ZtS

8 72111

Inlcrccpl

0 22662112

Th~chncss (crn)

00218

dclla I. (cnl)

I0218 2.02 18

3 0218

4 0218 5 0218

60218

7 0218

80218

11 7218

lnlcrccpl

dV evy

(mV) 5 1126 9 5472

14 0664 1 11 6oM

23 2W6 27 6578

32 531

37 24611 40.5382

S l o p

4 6028516

dV avy (1tlV)

5.4014

10 1 I08 14 8832 19 7882

24 697 29 4562

34 187 19 1326 42 9104

S lop

Cuncnl Arm

(mh) (cnrn2) 4 2 5

Cuncnl Area

(mA) (cm"2) 4 2 5

1-h~kncss

(cm) 0 02111

rklla I. (cm)

10218

2 0218

3 0218

4 0218 5 0218 6 0218

7 0218

80218 8 7218

Inlcrccpl

0 185813

f hlckncss

(cm) 0 O2!8

dclta I.

(W 10218

2 0218

3 (1218

4 Q218 SO218

6 0218

7 0218

80218 11 72111

lrrlerccpt

dV avg

OnV) 5 3152 9 979

14 7952

19 665

24 1648 29 43311

34 3512

39 0286 42 7278

S lop

4 857bl 12

JV avy

(mV) 4 6536

11 6888

12 7796

16 907 ? 1 088

25 1692

29 2694

33 4258 36 77611

Slllpc

Tcrnp

((3 3 5

dV I

(mVI 5 73

I 0 445

15 432

20 376

25 472 30 575

35 646

39 94

42 78

Hcsrsta~rcc

(ohms)

0 0729272

Tcnlp

(C) 35

JVI

(mV) 1731 8 907

13 I97 17 377

21 665

25 836

30 151 33 967

37 258

Rcwancc

(ohms)

Cuncnl

(mA 4

d V2

(mVI 5 158

9 ti26

I4 618 I9 316

23 748

28 736 33 769

38 518 42 726

Canduclrv~ly

(Sfcm) 0 1195713

Cuncnt

(1nA1 4

dV2

(mV1 4 392 8 585

12 612

16 768 20 94')

24 8117

28 806

33 19

36 156

C'onducl~v~ly

(SlcnlL

Arca

{cmA2)

2 5

dV3

( I W 5 319

10 039

14 772

19 526 24 287

29 516 34 337

39 16 42 324

Hcs~stlv~ly

(elm cm)

8 3632 132

Arca (cmA2)

2 5

dV3

(rnW 4 689

8 628

12 702

16 571 20 645

24 844

28 701

32 964

36 907

H ts~s~~v l l y

( u l ~ n ~ cnll

DATA FOR SINGLE. UNPRESSED MEMBRANE IN 1 .O M 1-l2SO4 AT 2S°C.

Tcmp

( C l 25

Cuncnl Arca

(mA) (cmA21 4 2 5

'thiclncss

(cm1 O 022

Jclia L

{ c n ~ ) l 022

2 022 3 022

4 022

5 022 b 022

7 022

LI 022

8 722

lnicïccpi

ï c i i ip Cuncni

(Cl (nr A) 25 4

Arca

(cm"2)

2 5

dV3

imV) 4 983 9 328 13 621 18 165

24 43 26 62 1

30 928

35 502

38 554

Kcsislivily

(ohm cm)

dV avy

(i1iV)

5 36215

9 4224 13 6611

I 8 0584 22 3692 2b 7078

31 1492 35 5138

38 7426

Ke~istuiiçc Coirhuciiviiy

(ohms) (Slcm)

Cuncnl Arca

(mA) (cnb'2)

4 2 5

Tciirp

(Cl 25

d V I

( m v ) 6 O51 I O 465 14 927

19 919

24 5 8 20 O11 l 33 569

38 231

41 672

Hcsisiiiiicc

(cd~iirs) O 24724 138

Cuncni Arta

irnA) (cin"2)

4 2 5

dV uvy

(mV) 4 6866 8 612

12 5412 16 4586 ZL) 454b

24 5428

28 6 l l 8

32 MI1

35 5 8 M

dV avy

imV1 5 6062 10 1428 14 7086

19 269 23 7608

211 4 148

32 9132

37 31544

40 Y844

Slqc

4 5 7 0 1 W

Intcrçcpi C'oiiduciiviiy Hcsisiiviiy

(Slcrn) (ohni car) 0 03559275 28 09561 14

I Conimcrcial ntcnibranc

Tcmp

((3 2 5

I 0M H2SO-l I Coinnicrcial rncmbraitc

I'hiclncss Tcmp

(cni) (Cl O 0218 2 5

Cuncni Arca

imA) (cin'2) 4 2 5

delta 1.

(cini 10218 2 0218 3 O218

4 0218 5 0218 60218 7 0218

8 0218

8 7218

J V nvy

lmVI 4 738 117116 12 7802 16 865

>O Y4411 24 <)Y911

29 09Ih

33 141

36 201

dV4

(ni V) 4 446 8 623 12 432 I b 64.1 20 Y32

24 822 28 717

32 787

35 971

Ci~nductiviiy Hcsisl~vity

(Sicm] (ohni cm) Rrusîivily (ohm cm) 16 MO378

lntcrccpt Slopc Nesistancc (ohms)

Cuncnl Arca

I n i N (cmA?) 4 2 5

Iiiicrccpi Sbpc Hoisiaiicc

(01111~5)

- c - g,a-~,,monm 2 ~ 1 5 ; - - * * m * - - - - c - o s - e 32: a - o = , = = ~ ~ o n n - m m - 3

0

- * A ?

-. - + a - T N + P - - -

a 9 - - -

E L - p H s ~ " ~ ~ ; $ = 2 " - a g A = - - ri , H O ~ P ' - = J ~ - = CI CI C. rt $ = a x 2 3 -

DATA FOR SINGLE, IJNPRESSED MEMBRANE IN 1.0 M W4 A?' 3 O C .

dclia 1. (cin)

I.0218

?.O218

3.0218

4.0218 5 0218

6 O218

7 0218

8.02 18

11.7218

Tcnip Cuneni

(c) (rriA) 3 4

d V nvy ( inV) 6 338 11 414 16.659

22 066 27 7326

32 70911

311 041 43 363

47 1608

d V 1 (n i V) 6 361

11.25 16 632

22 219 27 739

33 207

38 O5 43 592

47 948

Arca

(cniA21 2 5

JV3

i n W 6 938 11 836

17 176 22 b66 28 026 33 26

311 712 44 431 48 434

Rcs~stivi i y

(ohni cm) 20 1799917

Aica

(cni"2) 2 5

dV3 (mV) 6 208

11 20 16 329

21 71 27 711 32 283

37 906

42 82

47 005

Rcsistiudy

(ohm cin)

Thichncss

{c in i O 02 111

Jclta 1. (cm)

1 O218 20218

3 02111 4 0218 5 0 2 t h 6 02L8

7 O21ll

8 0218 11 7218

Intcrçcpi

0 534W8

I Llcklicss

(~111) U O218

dclia 1. (Clli)

10218

2 0218 3 0218

4 W I B 5 0218

6 0218

7 02111

80218 8 7118

l l i i t iccpl

O 7iWO44?

l'crnp C'unciii

(mA) 3 4

Slope Rcsoiaricc Cor iduci i~ i iy (olrms) (Stcni)

Arta

(cnP2)

2 5

dV3

(niVI 6 254 11 126 16 477

11 699

27 148 32 244 37 452

42 727 46814

Hcs~siivi iy

(ohm cni) I l 6581293

Arca

(cmA2) 2 5

dV3

(mV) 6 439

11 316

16 631

22 164 27 455

31 957

38 42

43 224 47 242

Hcsis~ibily [ o h f in )

DATA FOR SINGLE. UNPRESSED MEMBRANE IN O. 1 M 1-I2SO4 AT 25OC.

Jelia 1. (cil, ) 1 022 2 022

3 O22

4 022 5.022

6 021

7 011

LI 022 El. 722

d V ovy

4n1W 35 3684 66 953 98 6264

131 224 163 6b2

196 322

229 828

262 172 285 6011

Sltqir

dV avg

(n iV I 37 192

69 3234

101 9456

134 942 167 86

201 338

233 838

266 278 292 OOll

Tcmp KI 25

d V avy

( inVI 38 7826

73 2802

106 252 141 25

175 16

210 18

245 442

279 354

306 426

Slopc

Currciil ( i n W

4

dV2

(11lV)

36 615

71 462

104 199 137 21 IbY 117 203 07

235 114

266 62 2% 67

Cuiiduçttviiy (Slcin)

0 OL0534115

Cuncni

(mA) 4

dV2

i m W 40 458 75 317 108 683

141 56

174 45

209 83 145 83

280 75 305 14

l o i i d i i c i i ~ i i )

(J lc in l

A r a (cm"))

2 5

dV3

(mV) 36 957

67 662

99 963 134 79

169 03

200 51

232 32

265 25 289 11

Hcsisiiviiy (ahni cin)

94 9230193

Arca (cni'2)

2 5

dV3

(iirV) 39 294 74 729 105 468

141 65 176 OB

210 39 243 59

277 48 303 29

Hcriritvily

(0Illll cm I

U -I

a - , I P * H n s e s u n o S E " " " œ - " " " - 9 3 2 F I C T ~ O ~ ~ G ~ + ~ = 5 $ a b - $ 2 z z c s q g z e z

= c

DATA FOR SINGLE. UNPRESSED MEMBRANE IN 0.01 M Hlmq AT 25OC.

19mp

(Cl 25

dV l

( inVI 281 96

524 7 727 111

997 27 1232 6

1493 1 1757 6

1986 5

2163 7

Hcsisrancc

(ohms) 7 84905594

Cuncnt

i m A ) 4

dV2

(mV) 291 83

514 47

75P 79

091142

1251 7 1496 2

1738 2 2077 5

2144 2

Çonduc~ivi~y

(9cin)

O 001 121 15

Ternp I'uncnt

(mA) 25 4

Arca

tcm"2) 2 5

dV3

imV) 288 22 517 43

768 14

1024 4 1261 9

1.195 5

1752 8 3 1 8 5

2 194

Rcsistiv~y

(uliin cm)

891 9311175

Arca

(cinA2 )

2 5

dV3

(m V i 263 62

S M 09 751 57 497 35

1245 1 14112 3 1737 2

l W 2 6

21706

Hcsrsiivi~y

(ohm cm)

Thrckncss

(cm)

O 022

dclia 1.

(cm)

1 022

2 022

3 022 4 02,

5 022

6 022

7 022

II 022

8 722

Intcrcrpi

dV avg

(mv) 165 344

501 568

745 122 9118 07 1230 54

1472 8

I 7 l Y 48 1967 18

2140 16

Slopc

243 674875

JV i v g

i n ~ V ) 262 174 49B 098

738 298 9 W 6118

1224 08

L4h7 58 1 7 0 9 6 6

1953 26

2131 54

S I ~ K

7 cmp

(Cl 2 5

dV I

(mV) 256 38

498 72

737 47

989 29

1230 5

1481 3

1726 1976

2146 6

Roisiaiicc

(ohms)

3 82769666

C'uncnt A r a

( m A i (cin"2)

4 2 5

Tcrnp Cuncni Arca

(CI (mA L (cmA2]

2 5 4 2 5

DATA FOR SINGLE MEMBRANE HEATED TO 1 70°C IN 1 .O M H2S0.j AT 25OC.

Tcnip Cuncnt Arca

(cl (riiA) (cm'2) 25 4 2 5

Hcsistancc Conduct~vity Rcsistiv~ty

(ol~ins) (Skm) (uhni cm)

O 1 396535 O 05671 111 17 633008

'1-emp Currcni Ar-

(Cl imA1 (cmA2) 25 4 2 5

dV ar'8

i n iW 4 5798 8 325

12 455b 16 4564

20 4398 24 61311

211 57126

32 7013

35 6036

Slopc

4 0408625

dV avg

in iV) 4 5272 8 4874

12 4134 16 528

204102 24 4098

28 3392

32 3614

35 3526

Slopc

3 '/ 'xM403

Tcmp

K) 2 5

dV I

(mVJ 4 87 7 643 12 497 16 729

20 489 25 67

29 601

33 051

3b 1

Hcsistanct (olims)

0 086853

Cuncnt

(~ IA) 4

d V2

(mV) 4 498 8 565 12 438 16 348

20 404 24 L I

28 221

33 304

35 1175

Conduct ivif y

(Slcm) O 091 1886

Hcustancc C'onduclisiiy ( o l l l s (S l~ l i l )

Arca

(cmn2)

2 5

dV3

(niVI 4 431 8 385 12 483

16 241

20 382 24 34

28 464

32 348

35 335

Hcsidi~i ty (ohni cm) IO 966213

A r a

(cmn2) 2 5

dV3

(niV)

4 461

8 31 12 267

16 554 20 377

24 553

28 41

32 313

35 309

Hcrisiiviiy

(oliiri cin 1

nate 11 0400

dV4

( m W 4 52 8 507 12 406

16 468

20 387 24 411

28 2443

32.437

35 353

Daic Il 0400

dV4

i m W 4 541 8 538 12 485 16 407 !O 457 24 432

28 24

32 535

35 4M

DATA FOR SINGLE MEMBRANE HEATED 7'0 1 70°C IN 0.5 M HzSo4 AT 25OC.

Thickness

(cn1) 0.0198

dcLa L

(cm) t 0198

2.01911 3.0198

4.0198

5 Ol9lI 6.0198 7.01911

8 0198 8 7198

lnrerccpl

0.232343

Tcmp

(C) 25

JV I (mVL 8 627

I6 034 24 24 32 OW

41 311 49 385

57 142 65 736 71 I24

Hcs~stanct

(ohm)

0 0984761

Cuncnt (1nN

4

dV2

(mV) 9 085

16 857

24 68 33 019

39 353 49 507 57 269 66 199 71 92

Conductrv~ty

(Slcm)

0 0804256

dV avm

(mV1 8 9444 16 6562

24 74411

32 7446

41 1198 49 3632 57 29116 b5 7518 71 659

Slop

8 1596702

dV2

(mV) 8 781

17 I87

24 Ell 34 027

41 MI 48 942

57 65 392

71 494

Hcsrslancc Conduclrv~ty H e s ~ r ~ ~ v i ~ y

(ohms) (Slcw) (ohm cm)

0 1753808 0 01151589 22 144042

'r'crrp Cuncnr Arca

(C) ( nlA) (cmA2) 25 4 2 5

Temp Cuncnl Area

('3 (cni"2) 25 4 2 5

JVZ

(mV) 8 351 15 5117

23 165

30 375

37 163 45 976

53 544 60 663

66 304

dV avg

(mV1 11 463

15 4142

22 821 30 636

3B 028

45 83768

51 8548

bO 2396 66 3552

Resrsra~~cc COI~IICIIVII) Rcslstlv~~y (ohm) (Slcln) (ohm cnr)

0 I1112707 OM3b9lb 2 2 887713

Hcs~uarlcc Ct~ndua~vay Hcsnr~v~~)

(ohms) (Sfcml (olltn cm) 0 I4641131 00540677 I8 495339

DATA FOR SINGLE MEMBRANE HEATED TO 1 70°C IN 0.05 M 1I2SO1 AT 25OC.

Temp Cuncni Area

(Cl (mA) (cm"2) 25 4 2 5

Thickncss

(cm 1 0 0198

delta L

(cm) 10198

2 0198

3 0198

4 0198

5 019U

6 Ol98

7 O198

8 0198

8 7198

lniercepl

-0 6197as

1 cmp

(CI 2s

dVI

(mV) 65 054 123 46

184 66 247 81

306 32

370 28

430 2 491 64

538 28

Hcsisiancc

(ohms) O 148281

Cuncni

(mA1 4

dV2

( n W 63 995

124 21

183 48

244 73 304 49

368 53

428 32

492 49

536 4 1

Conduçiivit y

(SIcm)

O OS34121

Ar ca

(cm ' 2 ) 2 5

dV3

(mV) 63 066

122 58

183 57 242 73

305 17

365 19

429 48

490 04

536 3

Hcsistivit y (ohm cni)

18 722348

dV avy

îmVi 65 2462

122 63 182 468

243 524 303 992

363 602

424 842

411s 748

53 1 b42

Slopc

60 524626

dV avg

imV) 63 9244

123 316 183 &û6

244 622

305 111

367 752

428 912

49û 496

535 764

Slope

61 258038

Hcsiaiancc Ci>tiductivity Hesisiivi~y

(ohiiis) (Sein) (ohm cm) O 506762 1 0 01 56286 63 985 IO8

O\ l'hickncss 4 (cni)

0 0198

Tcnip Cuncn Aica

(Cl (mA) (cmA?)

2 5 4 2 5

Cuneni

LmA) 4

Daic

21 04 00

dclia 1.

(cm) I 0 IW

2 O198 3 Oli,U 4 OI!M S 01911

b O l rlii 7 0198

80198

8 7198

Slopc Rcsisiance L'uiiduciiviiy Rrsirtivily (olinis) (Slciii) (utlm c m )

Q 2620432 O 03O2?4 33 0862511

Slopc

DATA FOR SINGLE MEMBRANE HEATED TO 1 70°C IN 0.01 M H2SQ AT 25°C.

Tcmp

(C) 2 5

d V I

( n i W 235 94

46641 b76 39

911 46 110871

1x2') 4

1556 1 1771 1 1950 I

Hesislaiicc

(obins)

2 3409207

ï'cnip

( C l 25

d V 1

i n W 228 81

451.57

659 4 068 55

1095 47 1324 8 1536 2 1767 1 1938

Htstslaiicc (oli11,s)

C'uncrii

I i nA) 4

dV2

bnV) 226 42

445 91 666 0

881 71 111078

1325 1 1543 3 1763 8 19l l l 6

C'oi~Iitcliviiy

( S h i )

O 00331133

Cuncni

(mA) 4

dV2

i rnV i 213 79

450 911

664 9

879 62

1101 52 1311 9

1535 1 1755 2

1932 5

L'onduciivii y

(Slctn)

Arca (cm"?)

2 5

dV3

(mV) 231 08 448 38 664 63

881 07 1 IO8 36

13O8 8

1535 1 1748 2 1920 6

Rcsisicviry

{ohiii civ)

295 5108

Arca (cinA2 J

2 5

dV3

I m V ) 235 25

444 31 670 9 075 55

1107 29

1315 4 lS4iJ 7

1761 1 1938 4

Rcsisiivity (ohon cm)

Tcnip

(C) 25

dV I ImV)

241 27

456 29 677 23 909 47 1142 67

1363 4 1587 3 1822

1991 3

Hcsisiancc

(akins)

1 8266699

A r a

(cmA2) 2 5

dV3

OnV) 238 8

466 66

686 91

912 13 113697

1357 9 1580 5 1 fi011 7 1985 2

Hcsisiiviiy

(oli i i i cin)

23064014

DATA FOR SINGLE. PRESSED MEMBRANE IN 1 .O M HISOl AT 25°C.

Thickncss

(cm) O 0193

dclta 1.

(Cm)

10193

2 0193

3 0193 4 0193

5 O193

6 O193 7 0193

8 0193

8 7193

Irilcrccpt

O 5191899

'l'liickncss

(cm) O QI93

dclia 1. (ciii)

1.0193

2 0193 3 0193

4 0193

5 0191

6 0193 7 019.1

8 0193

8 7193

I i~crçcpi

(1 3616U42

Cuncnr

(mA) 4

JV2

(mv) 4 438

8 408

11 655 16 59

2 0 345

24 493

21 385

32 413 35 276

Conduclivily

(~CJII) 00515291

Arca

(cmA2) 2 5

dV3

iniV) 4 477

8 392

12 526

16 503

20414

24 392

211 359 32 207

15 234

Reastivrty

(ohm cni) 19 406495

Arca

(cniA2)

2 5

dV3 (11iV) 5 313 9 704

14 156 18 8.12

23 IXX

27 75

32 284 37 245 40 1112

Hcsistit iiy LoJ,rit ElIl)

Darc

23 12 W

dV4

(mV) 5 069

9 188

13 LTW 18414 22 60

27 117

31 432

35 877

19 181

I>aic

26 1299

dV4

(inV) 5 395 9 923

14 39 19 233

23 852

21) 339

32 613

37 066 40 681

ni ickncu

(cm) U 0193

Jelra 1- {cin)

10193

2 0193

3 0193

4 0193

5 0193

b O193

7 0193

8 0193

8 7193

lnlcrccp~

0 423OiW

1 hickncss

@an) 00193

Jclia 1. (CiIl)

4 0193

2 0193 3 DI93

40193

5 0193

b 0193

70193

8 0193 11 7193

Iiilclccpl

(J 17Yontl.l

JV avy

(~ IV ) 4 3998

8 4242

12 435 16 4538

20 328

24 3636

28 2352

32 1394 35 0596

Sliipc

3 9673718

dV avg

OnV1 4 488

84596 12 4654 16 4664

20 4888

24 4226

2846IJ

32 4018 35 402

Slupc

4 W33?YY

Tcmp lunc i i i

(Cl OnA) 2 5 4

Hcsisiaiicc Conduciivity

(ohms) (Slcin) O 1249103 OU611M4

'I'hrcknesr (Ciil)

O 0193

l cmp Cuneni Arcs

(cl (mh) (cniA2) 25 4 2 5

dclia 1.

(cnl) 10193

2 0193 3 0193

4 0193 5 0193 6 0193 7 0193

80193 8 7193

dV avy

(iriV) 5 3984

9 9178

11 b42U

19 325 24 1034 28 5742 33 9584 38 1702

42 1478

SI+ Hcsisiiincc Çonduciiviiy Rcsiriiviiy

(ohiiis) (Ycni) (ohni cni)

4 8532381 O 1223734 O CM0856 15 851474

Inicrccpi Hcsrstancc C'oiiduciivity Hcs~slivity

(ohms) (Stciii) (oliiii cni)

01039845 O07424111 134494911

Tcmp (Cl 2 5

Cuncni (iiiA)

4

'i'cnip Cunciii Arca

(C) i inh) (cniA2) 25 4 2 5

dV avy

( r W 5 1314

9 554

14 001

18 4254

1.1 I 302

27 3598

31 9124 36 3744 40 4B44

dV4

(mV) 5 155

9 80j

14 174 18 556

23 123

27 482

31 714 37 IO? 40 40ll

dV avg

(tnV1 5 2246

Y 8284

14 1034

18 7222

23 4654

27 11958

32 7414 37 1346 40 8218

Hcsisiaticc

(oliiiir)

O I l60503

Hcsislivl~y

(ohm cm)

15 032426

Hcrislancc Coi~d~~ci ivi ly Rcrib~ivity

(olims) (Slcm) (ohnt cm) 01073195 00719347 13901489

DATA FOR SINGLE, PRESSED MEMBRANE IN 0.05 M H2S04 AT 2S°C.

Tcrnp Cuncnt Area

(C') (mh) (cmA2) 25 4 2 5

Tcmp Current

(C) 25 4

Area

{cnrA2)

2 5

dV3

(mV) 6 5 64

I 2 8 45

I 8 8 35 251 61

314 75 372 45 434 26

497 99

542 15

Hcrrsllv~ly

(uhrn.ca)

Hcs~stancc C o ~ ~ d u c ~ ~ v r t y

(ohms) (Slcm)

Thickness

(crrr) 00193

Tcmp

(C) 25

Arca

(cmA2) 2 5

dV avy

(mVI 64 9328

116 126

187 ?I6

249 151

3 lU60( , 370 798

431 652

494 004 542 384

d V avy

(mV) 63 6516

125 488 183 142 243 594

104 82

365 28

424 9J

All5 924 53 1 05t1

Rcnstlwty (ohm cm) 82 023445

DATA FOR SINGLE, PRESSED MEMBRANE IN 0.01 M H2S04 AT 2S°C.

d V uvy

(mV) 2211 028

445 544 t h 3 8.12

8K8 448

I l l 6116

1338 02

1550 28

1759 14 1920 62

Slopc

2 10 96874

d V avy

(1nV) 257 704

4 W 352

714 115 Y54 182

1488 146

1423 66

1655 26

1902 14 2084 12

Slopc

236 167112

Ciincnt

( in A )

4

JV2

I n i V i 21908 433 88

bM 35

874 38

1108 32

1341 7

1550 1 1763 11

1933 4

C'onduciiviiy

(Slc111) O au35554

Currcni

( i n A l 4

dV2

{rnVL 259 bb

4115 35 713 22

950 35

I l 9 2

1417 6

1657 2 1915 3 2104 2

C'ondiicii\iiy

4 Sicni)

Arca

(cmA2)

2 5

dV3

(n iV I 242 92 46h 5 I 655 46

912 58

1141 23

I j b ? 3

1594 h 1790 1 1935 2

Rcristivriy

(ohni CIII)

281 26515

Arca

(cinA2 )

1 5

JV3

( m V I 252 3ti .(Y6 9

712 18

96(, 57

119') 13

1441 6 1 M B b

19111 2096 9

Rcsisitrii)

lulitri cni)

Chichnesr

(cin)

00193

&ha 1.

(cm) 1 0193

2 0193 3 0193

4 0193

5 0193

6 0193

7 0193

110193

8 7193

Inicrccpi

2 3400129

I 11ickiicu

ICi i I )

O O193

&lia 1 . (crn) l 0193

2 0193 1 0193

4 0193 5 0193 6 0193

7 0193

8 Ol9.1 8 7193

I1ilciccpl

2 IYY42Y2

J V aby

I n l v ) 242 648 462 152

685 O4

911 5

I l 3 1 456

1354 86

1587 08

1821 4

1993 64

Slopc

226 bû748

d V avg

(11lV) 239 5 M 469 03

688 324 920 676

I l 4 5 098 1372 118

1604 74

11131 54 2008 W

Slopc

228 6571

Tcinp

(Cl 2 5

d V I (1ilV)

244 34 447 16

66.1 (17

887 79

I I 0 9 9 3

1343 7

1569 LI lm04 9

l98b 8

Hcsistancc

(uhms) 1 6783843

1 cmp

(C) 2 5

dV I înlV)

246 21 477 91 694 1

YI8 45 1147 35 1376 2

1601 5

11122 4 2005 3

Rcrisiairc

(obins j

Arca

(cni"2)

2 5

dV3

( inV) 241 19 467 77

695 16

92 1 95

I l 4 4 79

1366 8

1609 5 1839 11

20011 7

Rcsis~iwly

(cihm cm) 2 17 40729

Arra

(çmA2i 2 5

dV.1

( m V i 241 78 460 66 679 2

923 19

1147 05 1373 3

1617

18.12 9 2023 7

Hcribiivtty (olitn ciil)

Date 13.01 Oû

dV4

( m V i 240 32 471 26

695 85

927 22

I I 4 4 31

1361 9

1590 7 11127

1993 6

Uatc

14 01 00

dV4

(n iV I 238 58 477 44 701 25 933 94 1155 46 1376 7

161 1 1

1830 8 LOOK 4

DATA FOR TWO MEMBRANES PRESSED TOGETIIER IN 1.0 M llmi AT 2S°C.

'I'hickncss

(cm) O O397

dclia 1.

( c m 1 O397 2 0307 3 0397 4 0397

5 0397 6 0397

7 0397 8 0397

8 7397

Iii1ciccpt

O 9Ol4Ub3

Cunenl Arca

ImA) (cmA2) 4 2 5

Arca (çm',2)

2 5

Hcsisiibiiy (ohm cm) 111 3656011

I liichncss

(cm) O UJI44i

dclia 1. (Cm)

1 01144 2 M l 4 4 3 05144 4 04144

5 04144 6 04144

7 03144 8 0414.1

8 74144

lnlcrcepl

l 23b2b27

A r a

(crnA2 2 5

dV3

( niV i 5 498 Y 135 13 245

17 27

21 368 25 366 29 277 33 366 36 238

Hcsis~ivity (ohm cm) 21 I43Mb

Thicknos

(cm) O 0374

dclia L (cni l

1 0374 2.0374

3 0374

4 0374 5 0374

6.0374

7 0374

il 0374

11 7374

Intcrccpi

1 0334233

Arca

(cinA2) 2 5

dV3

( n i W 11 154

15 1111 21 717 28 4118

35 341

42 157 49 418

56 43

60 932

Kcsisiiviiy

(uhiii cm) 21 585256

Arca

(cinA2)

2 5

dV3

( m v ) 7609 14.916

22 045

29 092

36 534

43 465 50 5112 57 678

62 685

Hcsisiivrty

(ohm cm)

dV ary

(mVL 7 8324 14 9242

22 011 29 1142

36 3lûb

43 4196

50 593 57 b326

62 773

S l w

7 1315127

Kcsisiancc Conduciivity

(ohms) (Yçm)

Hcststancc Ci~nduci iv~iy

(iihiiis) (Slc~n) O 3229154 O Wb3279

I'cinp Ciincnt Aica

6 - 1 (i i iA ) (cmA2) 25 4 2 5

c p Cuncril

( C l (n iA l 2 5 4

dV avg

m V ) Y 0972

16 3268

23 7106

J I 4188 38 9574

46.5048 54 0412 61 5976

67 1798

Rcsi~iaiicc C'ondiictiviiy Rcsistir ity

(ohiiis) (Yci i i ) (ohm cm)

0 292Sb4J2 O (J5MS67 17 fi501 7 1

Rcsisiancc Lonductivity

(ohinr) (Slcin) 0 5178416 UU52ISI I

Rcsiuiviiy (olllli Clti)

1') 174111

Thickncss

@ni) O O374

d e l ~ L

(cm) 1 0374 2 0374

3 0374 4 0374 5 0374 6 0374 7 0374

I 0374

8 7374

Irilcrccp~

1.909H93

8 'I'hickncss (cm)

0.04 144

d V iivy

(mV) 34 8776

O8 151 LOO 1266 133 002 IM 836 196 526 229 442

261 44 2114 128

Slapc

32 296625

dV avy

OnW 36 741

48 51)12

101 31211

134 532

167 112 200 184 233 134 266 626 291 144

Sloyc

3.1 07 1 1 h

Tcmp

[Cl 25

dV I

imV1 36 268

70 203

100 478 133 25 164 72 196 07 228 29

261 52

2114 22

Hcs~siancc

(ohms)

O 8019467

'I'cn~p

(C) 2s

dV 1

in)V) 35 932

68 61.1

100 613

133 25 166 33 199 72 233 O8 266 57 2%) 74

Wcsirlaivc

lal~ir~s)

Cuncni

(mA1 4

dV2

(mVi 34 817 67 551

99 626 133 47 164 I 197 SI 129 38

259 ll 283 59

C'ondw~iviiy

(Slcni)

O O 186536

Arca (cmA2)

2 5

dV3

(mV) 34 69

67 443

100 733 131 56 165 21 196 6

229 62

261 31 285 25

Rcsis~ivity

(ohm cm)

53 606062

1 liiclincss

(cm) 0 0397

&lia 1 (cm1

1 0397

2 0397 3 0397 4 0397 S 0397

6 O397 7 O397 11 0397

8 7397

lnlcrccpt

1 4W63l4

1 h~ckncss

(cm) ON144

delta 1. ( c W

I 04144

2 04144

3 04114 4 0.1144 5 OJI4.l 6 M I 4 4 7 04144 8 M l 4 4

11 7514.1

lnlcrcepl

O 0311268

d V avg

(niVI 31 9698 60 1002

88 2402 116 994 146 161 174 432 203 966

232 53 252 77

Slopc

28 729U29

dV avg

( m V I 36 0602

67 258B 101 0274

133 424

166 35 198 (114 231 724 264 W2 288 9211

Sll>pc

32 835?)0

Tcmp

(C') 25

dV1

imV) 31 03

60 065

86 816 I l 6 7 3 346 21 173 56 203 32

230 43

250 31

Hcsisiaiicc

(uliins)

O 6375594

Cuncni

( in4

4

JV2

iiW 31 284

58.708 86 874 117 123 146 3

175 66 203 64

232 25 253 32

Conduclivil y (Slcm)

0 0249079

Tcriip Cuncni

( C ) irnA) 2 5 4

Hcririancc C'onduciivity

(oliiiir) ( S h i )

Arca (cmA2)

2 5

JV3

(mv) 32 203

59916 B7 172 I I 8 888 144 411 173 8

202 97

231 30

251 23

Rcsistivily

(ohm cm)

10 147948

Arca

(cinn2) 2 5

dV3

(inVI 35 314

66 422 100 729 133 8 166 6s 1911 72

231 24 264 77 289 03

RCLIUIVLIY (rihiil cm)

Datc 13 O1 99

dV4

(mV) 32 186

61 604 88 623 1 16 309 147 25 176 24 205 47

233 71

254 56

Datc

16 04 99

dV4

(inVI 37 1411

67 Sbl

101 848 133 6

166 O7 198 45 231 83 263 48 288 45

dVS

imV) 33 146 60 208

91 716 115 92 146 57 172 9

2o.Q 44

234 I17 254 43

JVS

tmV) 36 165

bb 803 100 988 133 62

166 74 200 05 233 2 265 61 29a 97

DATA FOR TWO MEMBRANES PRESSED TOGETHER IN 0.01 M H + 0 4 AT 25OC.

'I h~ckncsr

(cm) 004144

dcllo I. (cm)

1.04144 2 04144 3 04144 4 04144 5 04144

6 04134

7 04144 8 04 144

8 79144

lntcrccpl

4 l 59605 5

Tk~ckncss

(ctn) 0 04144

Jclta L

(cm) 104144

2 04144 3 04144 4 04144 5 0.1144 b 04 144 7 0.1144

8 04 144

8 74144

lnlcrctpr

5 645.3149

d V avy (lt lV)

272 928 513 49

767 124 1027 194 127.1 788

I521 16 1775 82

2031 1 22 10 112

Slupc

251 94679

dV avy

(l11V)

273 732 524 026

765 02 1023 356 1279 06

1528 411

1780 I 2033 911

2219 68

S l o p

252 42687

l cmp

(C) 25

d V 1

(mV) 279 78 522 39

764 5LI

1023 16

1271 1 1509 I 17506

2002 5

2176 8

Hcststa~,cc (ohn~s)

3 6500701

Tc~rrp

(0 25

J V I

(mV) 274 81

526 56 768 24

1041 S5 1298 3

1550 4

I816 2062 9

2241 9

Hrs~srancc

(alms)

Area

(cm'2) 2 5

dV3

(mVI 262 211 502 I 4 762 6 8

1023 54 I272 4

I525 1808 5

2058

2236 7

Rcs~stit l ty

(ohm cm) 220 202 1 1

Area

(cmA2) 2 5

dV3

(mV) 260 44

512 37 766 24 I025 73

1287 1528 6 1782 3 2035 8

2237 7

Hcslst lv~~y

(ohm cm)

Date

I 5 M 99

dV4

(mW 272 8

5 0 9 74 767 71

1028 52

I259 1 1509 1 1763 4

2002 11

2185 9

D a ~ c

17 04 99

dV4

O W 285 3

528 11 765 3 1026 11 12W 7

1539 7

17B7 5

2045 4

2233 7

I elllp

(C) 25

d V I

(mV1 261 69 198 07 725 51 976 1

1213 3 1450 2

1701 5 1930 4 2098 3

Hcs~staricc

(ohms) 3 022437

Area (cmA2)

2 5

dV3

(mV) 251 811 467 19

702 47

937 78 1168.87

1406 8 1633 5

I863 4

2041 7

R c w s w l y (ohm ctn)

182 33814

Tcmp

(CI 2 5

dV1

îmV) 9 234

IS 572

22 436

29 566 36 407

43 737

51 395

58 285

63 305

Hcsisiaricc (ohms)

0 4006I9l

Cuncni

(niA1 4

dV2

(mV) 9 763

15 743

22 742

29 815 36 723

44 135

51 376

58 685 63 78

Conduçiivii y

( S ~ c i i i ~ 00546155

Daic

01 O4 Y9

dVd

i m v ) 9 136

16 141

23 271 30 439 37 742

45 495

53 136

59 354 65 361

Thickncss

(cm)

O 0569

delta 1. (cm)

1 0569

2 0569

3 0569 4 0569

5 0569

6 O569

7 0569

II 0569

8 7569

Iiilcrccpl

1 5580225

Tcmp C'uneni Arca

(cl i m A ) (cmh2) 2 5 4 2 5

Daic

1 1 02 99

dV4

i n W 9 O17

15 456

22 548 29 355 36 46

42 763

49 786

56 806 62 0 3

1 hichncss

(cm) 0 0547

dclia 1.

(cm) I 0547

2 0547

3 (15.1 7

4 0547 5 0547

6 OU7

7 0547

8 0547

8 7547

Iirtercepl

1 1122705

J V avy

I m V ) 9 3W

15 7426

22 857 29 837

36 1941

44 3344

51 721 58 6518

63 9506

S l w

7 133564

Hcscsinnçc C o o d i ~ i ~ v i t y Hcs~srivity (ohnrs) (Slciii) (ohm cm)

0 4837504 O 0170491 2 1 254409

l'crnp Cuncni Arca

(CI ( i i v î ) (cmn2) 25 4 2 5

Currcnr

imA) 4

d V avy

(inVI 11 9734

20 6502 30 28û6 39 32468

411 u774

58 3812

67 6702

76 7972

83 W b

Hcsisiancc Coidi ic i i \ i iy Rcris~ivity

(oliriis) (Sk i i l ) (oli in cm) U 5521313 O W l 9 J M 23 839951

Hcririaircc

( o h m ) O 1781711

Hcsiriiviiy

(olinr ci i i) 10 328934

DATA FOR THREE MEMBRANES PRESSED TOGETHER IN O. 1 M H2S04 AT 2S°C.

dclra 1.

(cm) 1 0547 2 0547

3 0547

4 O547 5.Q547

6 0547

7 0547

8 0547 87547

'1 cnip

(Cl 25

dV I

(mW 36 917 69 692

IO Wh

134 27 168 85 195 5

229 17

262 2 286 38

Rcsislancc

(ohiiis) 0 867S919

7'cnip

(Cl 25

dV I iinV) 36 65 71 5116

IO5 7472 142 63 172 40

209 25

240 18

273 87 297 111

Hrsirtaircc

(olims)

Cuncni

imA) 4

dV2

(mV) 36

68 lob 101 692

134 2

165 65

198 69

231 82

263 32 287 55

C'oiiduct ivit y (Slcm)

O O25?11)2

Cuncn~ (in A)

4

dV2

imV) 34 771 71 836

IM 532 13948 172 76

203 26

238 26

272 21 295 47

Cutiducitv~ly (Sm)

Arca

(cm' 2) 2 5

JV3

(nlv) 35 591

68 74 l 100 312 133 54

166 8 199 18

232 25

260 8 2117 22

Resirtiviiy

(ohm cm) 39 651374

Arca

(cm62)

2 5

dV3

imVi 35 652 69 462 107 595 138 96

171 35 206 84

237 53

271 75 295 16

Hc~isliviiy

(oliiii Cil,)

Daic 26 03 99

dV4

(mVI 36 431 69 486 '19 605

133 73

167 25

197 31

231 49

263 62 290 02

Cktc I I 0299

dV4

imV) 35 853 69 762

105 O13 140 39

171 74

2 M 75

2.1 1 0

273 26 297 65

JV5

(mv) 38 404 70 795 105 o is 139 82

171 73

205 89

2311 34

272 78 296 42

dV avg

( VlV) 36 6626

68 3202

100 b l l 8 132 L14 166 596

198 916

230 932

263 976

288 396

Slopc

32 656969

lémp

(CI 25

JV 1

imV) 37 2112 67 Bb

100 111 13299

166 91 19993

232 6

266 07 290 06

Rcsisiancc

(ohms) 0 763725

DATA FOR THREE MEMBRANES PRESSED TOGETHER IN 0.05 M H2SO4 A T 25OC.

Daic

22 03 W

dV4

4mV) 67 417 127 44 191 77 251 73 312 22

376 27

432 83

495 711 539 75

Tcmp Cuncni

i m N 2 5 4

Daic 25 03 99

dV4

(mV) 67 08

127.96 188 25 250 83 312 54

371 113

435 IS 495 36

539 61

Tcmp (C) 2 5

d V I (mV)

66 378

129 48

184 79 248 33 311 38

374 23

433 17

405 31 539 25

H c s i r i ~ i ~ c

{olitns) 1 5574116

Cuncni

i r W 4

d V 1

( n i V I 66 766 127 94

189 26

249 51 312 63

373 96

433 92

499 13 540 18

C'oiiJuciiviiy

(Slcml 0 Ol-i6l33

Arca

(cniA2)

2 5

dV3

(mV) 70 362 129 55 189 98 254 28 313 O5

371 77

438 17

500 26

540 69

Hcsisiiviiy

( o h cm) 68 430W5

Arca

(cinn2)

2 5

d V3

(mV) 68 I l 4 125 93

185 72 250 04

311 23

372 45

431 72 494 95

540 4

Hesiriivity

(alirii cm)

J V avy

(mV) 68 4096 128 764 189 633 251 il02 312 286

374 024

434 448

497 051 539 998

Slopc

61 287474

dV avg

( n W 67 3024 126 078

186 152 250 324 311 538

372 19

433 692

495 858

540 592

Slopc

61 547463

Kcsisiancc Conduçtiviiy

(ohms) (Slcin) 0 ‘MN2908 O O N I W i

'1 criip Ciincni Arca

( i n A l (cmA2) 25 4 2 5

Pcrnp Cuncni Arca

(Cl (niA) (cmA2 1 25 4 2 5

dclia 1 . (Cili)

L 0547

2 0547 3 0547 4 0547 5 0547

b 0547

7 0547 8.0547 B 7547

dV avy i m V )

67 5.134

127 7r)B

188 Olb 250 276 31 1 294

370 216

432 202 493 092 5.39 396

d V avy

(n iV I 65 3744

121 679

1111 54 240 68 300 482

358 76

421 27

482 332 526 97

Hcsistaricc Conduciiviiy Hcsisiiviiy

(olinis) (SIcm) (ulini ctn)

O5400919 OWOSllb 24t184275

d t =

c e - , * , , r n 1 o w . m in 2 - *

g l g F < ~ ~ = z z s z - s 3 5 5 u - - -. . ,oonnz;-g 3 - 8 u =

a - - d E Z S m a s - - - - - FI > & o = G : . . q n 2 2:; + 3 - 3 - r i Q , n - = m g g 2 - 2 7

P A h a - g ESb' w p c * * . ^ = " " g z ' : z " -1 .t C- , - ' 5 2 c g P d % E ~ ~ ~ ~ ~ ~ ~ I E ~ 1 - 9

n Z S =

'I'cmp

(Cl 25

I hickntss

(cm) 00215

Cuncni Arca

(mA) (cmA2) 4 2 5

dclia 1.

(cm) 10215

2.0215

3 0215

4 0215 50215

60215

7.02 15 8.02 1 5

8 7215

Inicrccpi Jlopc Rerrriancc (olinis)

O 8657332 1

C'onductiviiy Hcststiv~iy (Slcm) (ohin cm)

O UU99337LL i M) 60h652

Tciriy (Cl 25

Arca

(cmA2) 2 5

Daic 20 06 99

1 bichiicss

(cm) 002is

cklis L

(cm) 10215

2 0215 30215

4 0215

5 0215

60215 7 0215 80215

8 7215

Interccpi

2 23747858

Tciiip

(Q 25

dV I

(mV) 25 195

47 465 b9 757

Y1 415

I l 3 699

136 O9 159 il 17912 197 1 1

Hcrtstancc (alinisl

O 67939 1 .ib

Cuncni

imA) 4

dV2

(mV1 24 893 47 53 69 614

92 071

114 333

13605 158 91 180 14 196 95

Conducttvtiy ( S k m )

O O 126583')

I nlcrccpt

DATA FOR SINGLE UNPRESSED MEMBRANE IN 0.6M KCI AT 12°C.

JV avy

(mV) 33 2558

62 9502

91 2444 120 7576

I 40 oiie 178 76

207 72 236 992 258 49

Slopc

29 145350

J V avy

( InVI 32 1634

61 0312 89 7072 1 1') (193 Id? 378

175 464

204 42 733 02

255 018

Sl0~Ic

211 7U96PJ4

Cuncni

(n iA l 4

JV2

(inV) 33 75

63 073

91 393 121 42

148 8

179 lY

208 97

237 ll4 259 01

Coiiducttvi~y (SIcin)

O 00850957

Curreni

(mA) 4

JV?

i rnV1 1 1 93

61 757

90 005 120 86

1-18 75

176 71 206 58

234 68 257 l

Ci i i i duc l iw i~~

(Sicni) O OIIlI5476

Arta

(cm"2) 2 5

J V 3

(mV) 32 332 61 19

90 616

I 2 I b l

149 62

173 04

207 92

237 22 251 91

Hcsirtiviiy

(ohm cm) I l 7 513817

Arca

(cmA2) 2 5

dV3

(niVI 32 081

bO SM 89 861 118711 146 29

174 78 202 43

231 03 253 17

Rcsisrivity ( o l m cm)

98 1859289

Thickncss

(cm) 0021s

delta L

(cm) 10215

2 0215 30215

40215

50115

60215

7 0215

Bü2IS 8 7215

Inlcrccpl

3 16798307

I 'htckr~ss

(cm) 00215

d c l s 1.

10215

2 02 15 3 0115

4 0215 5 0215 60215

70215

80215

8 7215

ln lcrccp~

3 J7.WVO.l

J V avg

(11iV) 32 7484

61 6584 90 8862

1 19 57112

148 702

177 514

206 534

235 492 255 9l1i

Arca (cmA2 l

2 5

dV3

i m V ) 32 361

62 162

91 I I 4

1199 140 b

17841 207 7

236 47 256 21

Hcrirl ibi iy (uhiii CIII)

110 1'18122

A ~ c a

(cmA2) 2 5

dV3

i m V ) 32 29

6 1 212

90 221 120 304 149 02 176 87 204 99

234 53

256 37

Ho i r i i v i t y

(oliitl Clil) 1 1 O 29206 1

DATA FOR SINGLE UNPRESSED MEMBRANE IN 0.6M KCI AT SOC.

Thickncss

(cm) 0.02 t 5

dclia L

(cm) 1.0215 2.0215

3.021 5

4 0215

5 QZIS

6 0215 7.02 15

80215 8 7215

Inicrccpt

2 92 1 08564

Thickncss

(cm) 0.01 15

dclia 1.

(~111) 1.0215

2.02 15

3 0215

4 0215

50115

6 0215 7 a215

80215 11 7215

I nicrccpi

d V nvy (n iV I

40 352

76 I l 5 8

11 1 8652

148 07

183 894

219 174 255 6

201 804

117 552

Slopc

ï c m p

(Cl 7

d V I

( i n v ) 39 718

76 315

112 774 149 77

184 (>b

22U. 54

255 63 292 48

316 7

Hcsisiancc (oliiiis)

O 9237665

'i'cmp

(Cl 2

d V I (1tiV)

40 682

78 179

I I 2 159

149 1

183 M 219 86 255 IL7

292 49

317 07

Hcs~stancc

(ulliils)

Arca

(cmnZ) 2 5

dV3

( m V ) 38 951

76311 l u 0 W l

146

1113 27

218 511 256 Ob

289 92 315 68

Hcsisiivlly (ohni cni) 107 41471

Arca

(cmA2) 2 5

dV3

(mVi 40 251

76 113

112 351 146 74

183 27

219 16 254 84

291 77

317 11

Hcsruivit y

(ohrii cm)

l l i ickncss

(cm) 00215

&lia t. (cm) I O215 2 0215

3 0215

4 O2l5

50215

6 0215

7 0215

80215

8 7215

lntcrcept

4 0323 1918

i'hickness

( c ~ n ) 00215

dclia 1.

(cm) 10215 2 0215

3 0215

4 0215

5 0215 6 0215 7 0215

80115

8 7215

I i,iciccp1

Tcmp

(Cl 2

dV I

i m V ) 41 142 76 145

LI3995 149 113

Ill6 Il 271 2

258 01

293 52

318 84

Hcs~stancc (nhnis)

1 20036948

A r a (cm"2)

2 5

dV3

(mV1 40 87 l 75 751 1 IO 882

147 26

183 44 220 3

254 9

289 8 315 61

Hcsisiivity {ohm cni)

139 577847

Arta (cm'.2)

2 5

dV3

(inV) 39 807

75 501

112 74

146 93

183 39

217 36 254 03

289 88 315 83

Kcsislibity

(ohin CIII )

SECTION 2. SAMPLE CALCULATION OF D.C. CONDUCTIVITY

Thickncss

(cm 1 0 0215

dcita L (cm)

10215 2.0215

3 0215 4 OZ15

5 0215

6 0215

70215 8 0113

8 7215

Inta#p

2.89949984

dV avg dV 1

mV) (mm ~ . 8 9 0 6 24.775 47.6202 47.29

68.9294 68.554 91 8382 91.336 ll3.LdS 112.241

135 65 134% 157 U 6 156.81

179694 18044

195 824 19542

c m t m A )

4

dv? (mw

26.435

48.035 69.202 91.637

113 203

135.34 I58.56 180.12

195.76

Conductivity

Wcm) 001019681

Shown below is a plot of die average IR &op in column 2, venus delta L (the distance between the luggin tips) in column 1 , for the data at the left. The equation to descnbe the plot was generated by a linear regression.

Eq'n: dV = 22.05 1 x(cm) + 2.8995

Once the equation parameters were determined, the IR &op across the membrane was caiculated using the generated equation. The distance used in the calculation is equal to the thickness of the membrane.

- - -

Sampie dc conduclh,ity data for an untreated membrane in 0.6M KCL The conductivity was then calculated

using equation 1.

1 Distance (cm)

Therefore. the conductivity is calculated as follows:

Resistivity = o -' = (0.0 10 19)" = 98.07 ohm.cm = 0.98 ohmm

Figure 25. Piot of sampie data above, Dirronce benuten luggin tips is oloned apainst the IR d m .

SECTION 3. MEMBEUNE RESISTANCE DATA

HEAT TREATED MEMBRANE

(0.0198 cm thick)

ACID CONC'N (Ml

SINGLE M E M B W E COMPOSITE

(0.0193 cm thick)

UNTREATED MEMBRANE

(0.0216 cm thick)

TWO MEMBRANE COMPOSITE

(0.0395 cm thick)

THREE MEMBRANE COMPOSiTE

(0.0565 cm thick)

Tuble 10. ~Uembrme resktance data for dc conductiviiy merrrurements.

ACID CONC'N (Ml

THREE MEMBRANE COMPOSITE

UNTREATED MEMBRANE

ff EAT TREATED

MEMBRANE

SINGLE MEMBRANE COMPOSITE

TWO iMEMBRANE COMPOSITE

Table I I . Mmbrme resrStance per unit thicknpss.

SECTION 4. DATA AND CALCULATIONS FOR NAFION@ 117 IN PURE HzO

Ruo # Caod (Sm")

1.86E-03 2.39E-03

2.XE-03 2.50E-03

1.22E-03 2.26E-03 2.OSE-03 2.73E-03 1.87E-03 2.13E-03 2. 1 JE43

2.09E-03

2.4 1 E-03

2.17E-03 2. 1 JE43 2.44E-03

1.23E-03

Extrapolation of conductivity at an H? ion concentration of IO-' M.

Equation relating log conductivity vs concentration for single processed membrane (Figure 15):

y = 0.705~ + 0.8273, where y = log conductivity and x = log concentration. Log IO-' = -7

Therefore: y = 0.705*(-7) + 0.8273 = 4.1077 Therefore the conductivity at an H' ion concentration of 1 O-' M = I O ~ . ' O ~ ' = 7 . 8 ~ 1 oa5 ~ . m " .

APPENDM 2: A.C. EMPEDANCE DATA AND CALCULATIONS

SOLUTION AVERAGE CONC'N MEASURED CONDUCTIVlTY CONDUCTIVITY

(Ml (s.m-')

7

Pure Water 9.78 9.78 9.58

l 9.0 ! M H2S0,

I 5.52

I 9.!3 I

5.63

O.6M KCI 0.799 0.790 0.84

SAT'D KCI 1 0.780 0.799

Sfondurd deviation

Table 12. A L conducthity data us measured by conductivity mefer.

Experimental Temperature: 22.1 OC ES

Calculated ce11 constant (equation 2): - A

ES (electrode çeparation) = 1.5 cm; A (electrode area) = 0.02048 cm' ( l m x 0.02048 cm) 1 C 1 *J

Therefore: Ce11 constant = = 73.24 0.02048

APPENDIX 3: SECTION 1. MEMBRANE TITRATION DATA

AVERAGE ION EXCHANGE CAPACITY

(rneq. g-'1 CAPACITY

MEMBRANE DRY MASS TREATMENT (g)

NaOH CONC'N (Ml

Untreated

Untreated 1

Untreated 0.573

1 Baked at 1 S O C For 1 hour

-

Baked at 125°C for 1 hour

Baked at 125°C for 1 hout

Baked at 1 70°C for 4.5 min.

Baked at 170°C for 4.5 min.

- - - --

Baked at 1 70aC for 0.306 4.5 min.

Hot pressed at 1 70°C. 1600psi for 0.2885

90 sec

Hot pressed at 1 70°C, 1600psi for 03885

90 sec

1 70°C. 16ûûpsi for 02885 90 sec

I Standard deviarion

Table 13. Membrane ritration data

SECTION 2. S M L E CALCWLATION FOR ION EXCHANGE CAPACITY

Mass (g): 0.572 Mbls

Concentration (C) of NaOH ( - ): 0.0497 L

Volume (V) of NaOH (d): 10.54

Ion exchange capacity = IL Mols 1 Eq lOOOMeq 1 1

'mL) * 1 O O O ~ L xC(-)x- x -(-).

L :Mol Eq :\.las g

1 0.54m.L 0.0497~1 OOOMeq Meq Therefore ion exchange capacity = x =0.9162 - 1000mL 0.572g g

DRY M ASS.

Time = O

WET MASS

(g)

WATER CONTENT (gH,O* g-'1 1

MEMBRANE MASS at CWEN TIME INTERVALS

Untreated

membrane

Three membrane composite

ïhree membrane composite

membrane

Heated at 125°C for

Heated at 170°C for 4.5 min

Membrane composite

SECTION 2. CALCULATION OF MEMBRANE WATER CONTENT

MASS tg)

Shown below is a plot of membrane mass venus time for the single, hot pressed membrane (data s h o w at lefi). The equation generated for the plot was done using the Trend Line function in Excei. The dry mass of the membrane is taken at time = O sec, which is intercept of the plot. Therefore, the dry mass of this membrane is 0.2874 g.

The membrane water content was calculated using the following equation:

0.3437 - 0.2874 Therefore WC =

0.2874

Sumpie water uptake data for a single pressed mem brune

APPENDPX 5. MISCELLANEOUS

SECTION 1.CALCULATION OF ACTIVATION ENERGY

- . .

y=aQ)ti23c R =am Show to the left is the plot of log conductivity

versus inverse temperature for one Nafion@ membrane in -Ea

0.6M KCI. The dope of ihe line = 2.303R '

where En is the activation energy and R is the universal constant. Rearranging, Ea is calculated using he followi equation:

Therefore Eu = 640.93 x 2.303 x 8.3 14 = 12272 .J.mof'

Figure 27. Pfot of log conducrhriry vs inverse temperature for I Na@n@ I I 7 membrane in O.6M KCL

SECTION 2. C A L C U T I O N OF STAGNANT LAYER RESISTANCE

The lirniting current density and the actual ce11 current density are calculated and compared in order to determine the degree to which a stagnant layer resistance has a substantial effect on conductivity measurements.

The limiting current density iiim is given by the following equation:

where z is the ion charge, F is Faraday's number (96487 c.mol'l), D + O is the ion diffusion

Jc = L J - r d coefficient (9.3 1 x 1 o - ~ m2.s-'). Co is the ion concentration (1000 mol.m4), L is the ion transport number and 6 is the boundary layer thickness. An unstined solution typically has a boundary layer thickness = 0.OScm. t ~ , for the

ion in H2SOI = 0.8 14.

Therefore iiim = (1 - 0.8 i4)(O.OOO5)

current The current density at which the ce11 operates. i = = 4.OmA x (2.5 cm2)-' = 1.6 mAcm"

area The operational current density of the ce11 is 0.2% of the limiting current density. Therefore the

resistance due the boundary layer is negligible and should not affect conductivity measurements.

SECTION 3. CALCULATION OF ION EXCHANGE SITE CONCENTRATION

Ion exchange capacity (IEC) for Nafion@ 1 17 (meq.g dry membrane-'): 0.91

Average membrane dry mass (DM) (g): 0.34 14

Average membrane wet mass (WM) (g): 0.4665

Membrane wet density (p) (g.cm-3): 1 S755

fEL'(meq l g)xDM(g) lm01 Exchange site concentration (M) = x p cg. cm") x - .Y

1e9 W W g ) eq IOOOmeq

0.9 I(meg 1 g)x0.3414(g) :. conc'n = x 1.5755 (g.cmf3) x 0.00 1 meq'' = 1.0504~ 1 0" m01.cm'~ 0.4665(g)

= 1.0504~ 1 o5 rnolcm" x 1 O00 cm3LL" = 1 .O5 mol. L-'.

SECTION 4. GRAPHITE ELECTRODE FAMUCATION

The electrodes used in the hot pressing experiments were fabricated using the

follouing procedure:

0.3g of KETENEILACK EC300J carbon powder (Azko-Chemie) and 10.0 mL of

Teflon emulsion (DuPont) were dispersed in 30.0 mL of 1 .O M HCI. The suspension was

stirred and then agitated in a Cole-Parmer Mode18851 ultrasonic vibrator for 15 minutes to

ensure that there was no clumping of the carbon powder. The carbon powder suspension was

then applied by paintbwh to 35 mm disks of hydropbobic polymer treated carbon paper

(Stackpole). The suspension was applied to the carbon paper and allowed to air dry for 12

hours. This procedure was repeated twice (three applications in total). The electrodes were

then sintered for 2.5 hours at 300°C.

A solution of 5% wt (1 100EW) N&n@ (Appendix 5. section 5) was applied to the

electmde surface using a paintbrush and the electrode was allowed to air dry for I hour. This

procedure was repeated until there had been 20 applications of the Nafion@ solution to the

electrode surface. The electrodes were then sintered at 250aC for 1 hour.

SECTION 5. EQUlPMENT SUPPLIER INFORMATION

(1) Enerpac RC55 hydraulic piston, model A205 C clamp and model P-39 supplied by: Roy's Hydraulic Service Ltd, 379 Oakdale Rd, Downsview, Ontario. M3N 1 W7. Phone #: (416) 741 -5467.

(2) Marinite Board insulation supplied by: SouthPort Board Products, 140 Caster, Woodbrdge, Ontario. Phone #: (905) 85 1-2 140.

(3) CSS - 20 150 cartridge heaters, KTSS - 3 16 - 2 thermocouples and CN76000 PID duai output temperature conuoilcr suppiied by: OMEGA (An Omega Technologies Company), 976 Bergar, Lavai, Quebec. H7L 5Al. Phone #: (514) 856-6928.

(4) Nafion@ 1 17 membrane and 5% wt Nafion@ (1 100 EW) solution supplied by: Sigma Aldrich Canada Ltâ, 2149 Winston Park Drive, Oakville, Ontario. L6H 658. Phone #: (905) 829-9500.