4

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INORGANIC ION EXCHANGE MEMBRANE FUEL CELL

PERIOD ENDING 10 JULY 1965

prepared for

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

CONTRACT NAS 3-6000 -

6 5 31554 "I""'

https://ntrs.nasa.gov/search.jsp?R=19650021953 2019-05-17T09:17:58+00:00Z

. NASA CR-54460

QUARTERLY PROGRESS REPORT SM-46221 -Q4

INORGANIC ION EXCHANGE MEMBRANE FUEL CELL

by C. Berger and M. P. Strier

G. Belfort

prepared for NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

July 1965

CONTRACT NAS 3-6000

Technical Management NASA Lewis Research Center

Cleveland, Ohio Solar and Chemical Power Branch

Daniel G. Soltis

MISSILE & SPACE SYSTEMS DIVISION ASTROPOWER LABORATORY

Douglas Aircraft Company, Inc. Newport Beach, California

4

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NOTICE

This report was prepared as an account of Government sponsored work. Neither the United States, nor the National Aeronautics and Space Administration (NASA), nor any person acting on behalf of NASA:

A. ) Makes anywarranty or representation, expressed o r implied., with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; o r

B.) Assumes any liabilities with respect to the use of, o r for damages resulting from the use of any information, appar- atus, method o r process disclosed in this report.

A s used above, "person acting on behalf of NASA" includes any employee o r contractor of NASA, or employee of such acmtradmr, to the extent that such employee o r contractor of NASA, o r employee of such contractor prepares, disseminates, o r provides access .to, any information pursuant to his employment o r contract with IUSA, o r his employment with such contractor.

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TABLE OF CONTENTS

1,O SUMMARY AND CONCLUSIONS

2.0 INTRODUCTION

3 .0 EXPERIMENTAL PROCEDURE, RESULTS AND DISCUSSION

3.1 Fuel Cell Tests

3. 1. 1 3.1.2 3. 1. 3

3. 1 .4

3 . 1.5

Standard Fuel Cell Tests Compact Fuel Cell Life Tests Fuel Cell Tests with Palladium and Iridium Catalyst Material Fuel Cell Tests with Various Types of Tantalum and Stainless Screen Electrodes Fuel Cell Tests with Unitized Membrane- Catalyst-Electrode Structures

4 .0 FUTURE WORK

5 . 0 REFERENCES

6.0 PROJECT PERSONNEL

Page

1

3

4

4

4 6 9

9

11

12

13

14

SM-46221-Q4 ii

LIST OF ILLUSTRATIONS

Figure

1

2

3

4

5

6

7

8

9

10

11

12

13

Plot gf Voltage versus Time for Fuel Cell Tests a t 25 C and 65OC for Non-Impregnated C200B Membrane at 30 ma/cm2

Plot of FuegCell Res is tpces versus Time for Tests at 25 C and at 65 C for Nzn-Impregnated C200B Membranes at 30 ma/cm

Plot of Voltage versus Time for Various Percen- tages of Platinum Black Impregnated C200B Membranes at 65-2 C and Current Density of 30 ma/cm

+ o 2

Plot of Resistances Versus Time for Various Percentages of Platinum Black Impregnated C200B Membrane at 65220C

Polarization Curves for Inorganic Membrane Fuel Cell, Test 2 , Table I

Polarization Curves for Inorganic Membrane Fuel Cells, Test 3 , Table I

Polarization Curves for Inorganic Membrane Fuel Cell, Test 4, Table I

Polarization Curves for Inorganic Membrane Fuel Cells, Test 6, Table I

Polarization Curves for Inorganic Membrane Fuel Cell, Test 7, Table I

Polarization Curves for Inorganic Membrane Fuel Cell, Test 8, Table I

Comparison of Different Layouts of Grooves and Holes for the Electrode Facing Side of the Backup Plates

Three Types of Backap Plates Used in Astropower Compact Fuel Cell (Gas Compart- ment Face)

Three Types of Backup Plates Used in Astropower Compact Fuel Cell (Electrode Face)

Page

15

16

17

18

19

20

21

22

2 3

24

25

26

27

S M- 4 6221- Q4 iii

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LIST OF ILLUSTRATIONS (continued)

Page

28

Figure

14 Relationship of Areas of Four Different Types of Backup Plates Used in the Compact Fuel Cell Design

Relationship of Fuel Cell Resistance with Available Electrode Area Exposed to the Reactant Gas e s

15

16

29

30 Two-Inch Diameter American Cyanamid AA-1 Electrode and Platinum Black Deposit, Showing the Contact Points, Resulting from the Lugs of the Backup Plate

17 Inorganic Ion Exchange Membrane Backup Plate Sandwich, Illustrating Electrical Lead Off V i a (a) Backup Plates (b) Electrode Tabs

31

18 Large Compact Fuel Cell and Gas Distribution Insert

32

19

20

Large Astropower Compact Fuel Cell 33

34 Polarization Curves for Inorganic Membrane Fuel Cell, Test 9, Table 11

21 Polarization Curves for Inorganic Membrane Fuel Cell, Test 10, Table I1

35

22 Polarizatior? C ~ r s r e s f n r Inorganic Membrane Fuel Cell, Test 11, Table 11

36

37 23 Polarization Curves for Inorganic Membrane Fuel Cell, Test 12, Table 11

24 Polarization Curve for Inorganic Membrane Fuel Cell, Test 14, Table 11

38

Polarization Curves for Inorganic Membrane Fuel Cell, Test 15, Table 11

39 25

26 Photograph of Unitized Electrode-Catalyst- Membrane Configuration (Front View)

40

27 Unitized, Fused C200B Membrane-Electrode Configuration, Demonstrating Silver W i r e Leads Interwoven Through Electrode Screen Structure

41

SM-46221-Q4 iv

LIST O F TABLES

Table

I Summary of Significant Fuel Cell Tests on Pres int e red Zirconium Dioxide- Phosphoric Acid--" Zeolon- H" C200B Membrane Performed in the Astropower Analytical Fuel Cell Design

II Summary of Significant Fuel Cell Tests on Pres inte red Zirconium Dioxide - Phosphoric Acid-"Zeolon- H" C200B Membrane Tests Performed in the Astropower Compact Fuel Cell Design

III

IV

V

V I

Summary of Results of Analytical Fuel Cell Tests with Palladium and Iridium Catalyst Mate rials

Comparison of Resistance at 65: 2OC and Various Time Intervals for 20 Percent Platinum and Palladium Black Catalyst and a 50 /50 Ratio of Platinum to Palladium Black Catalyst Impregnated in the Outer One-Third Layers

Summary of Fuel Cell Test Results Obtained with Various Tantalum Screen Electrodes with C200B Membrane

Summary of Fuel Cell Test Results Obtained with Various Tantalum and Stainless Steel Electrodes with C200B- Platinum Impregnated Membranes

Page

42

44

45

46

47

40

SM- 46221-44 V

.

1.0 SUMMARY AND CONCLUSIONS

The emphasis during this report period continued to be on achieving

the maximum possible fuel cell performance. By incorporating the optimum

fuel cell design features with the optimum membrane- catalyst- electrode con-

figuration, it was possible to achieve the highest fuel cell performance level

for the program to dat.

range at 30 ma/cm . volts.

At 6SoC, the voltage was in the 0. 770 to 0. 780 volt

At 50 ma/cm , the voltage was in the vicinity of 0.71 2 2

The following is a summary of the more significant results:

(a) The best performing membrane contains 2070 platinum black impregnated to a depth of 570 of the total membrane thickness on both sides.

This quantity of platinum, constituting about two percent of the total membrane

weight, is of the order of 0 .07 grams per membrane.

screen-platinum black-Teflon electrode structure is pressed up against

this membrane.

the membrane.

affords no further advantage.

(b) Incorporating 270 Teflon into the outer layer of the membrane

A separate tantalum

Evidently the critical reaction zone is near the surface of

Deeper penetration of the membrane with catalyst material

a s water-proofing agent during the impregnation with platinum black has no

apparent effect on the fuel cell performance level at 65 C. 0

(c) Cycling this fuel cell between 65O and 102OC has no significant

effect on fuel cell performance; Teflon does appear to contribute to this

stability in performance.

(d) Constant performance levels up to 151OC were obtained for the platinum black impregnated- membrane (penetration of platinum black to

a depth of 570 of the total membrane thickness).

(e) Fuel cell performance improved with increased gas free- space in the backup plate, providing there was no loss of total contact area

between electrode and backup plate.

(f) A four-inch diameter platinum black- impregnated C200B membrane was successfully evaluated in a new enlarged version of the Astro-

power compact fuel cell. The maximum voltage was 0 . 7 5 5 volts a t 30 ma/cm

for over 200 hours of continuous operation at 65 C.

2

0

(g) It appears that a 50/50 platinum black-palladium black mixture

SM-4622 1-44 1

is a more effective catalyst system for impregnation into the membrane than

is either platinum black o r palladium black, alone.

mixture a re being intensified.

(h) In further efforts to improve fuel cell performance, fifty- mesh tantalum screen electrodes were evaluated by three different methods

for incorporating platinum black catalyst into the screen matrix, i. e. , electro-

deposition, paste and sintering techniques.

niques gave comparable fuel cell performance.

catalyst to the extent of 20 to 30 mg/cm

performance.

procfing purposes in the screen matrix.

some promise as a potential electrode material for this membrane system.

Studies with the 50 /50

It was found that all of the tech-

Loading with platinum black 2 appears to be the range for optimum

Silicone resins a r e about as effective as Teflon for water-

304 stainless steel (160 mesh) shows

(1) Unitized membrane- catalyst- electrode system with the three

components fused together through sintering have not as yet exhibited signifi-

cant promising fuel cell behavior.

electrode surfaces may be required for adequate fuel cell performance; this

may be a requirement for the three phase reaction involved.

A distinct interface between membrane and

(j) Fuel cell experiments with provision for wicking a r e still in progress.

SM- 4 622 1 - Q4 2

2 . 0 INTRODUCTION

During the previous quarterly report period, it was established that,

by improved fuel cell design a s well as by the use of platinum-impregnated

zirconia-phosphoric acid-" Zeolon- H" membranes, a fuel cell performance

level of 0. 65 volts at 50 ma/cm

Then, a new performance target level of 0. 7 volts at 50 ma/cm was established.

It was expected that this new goal could be attained by continued improved fuel

cell design efforts as well a s through more effective membrane- catalyst-

electrode configurations.

test under the most favorable operational conditions established to date.

2 2 (0.72 volts at 30 ma/cm ) could be attained. 2

The new performance goal was reached in a fuel cell

A larger membrane having a diameter of four inches also afforded

favorable performance characteristics under essentially similar conditions.

Attention was given to improving the membrane- catalyst- electrode

configuration, particularly from the standpoint of reduction of contact resist-

ances. It was found that the use of a 5 0 / 5 0 platinum-palladium black catalyst

mixture is a more effective catalyst system than platinum black alone.

The details of this work a r e presented in this report.

SM- 46221- Q4 3

3.0 EXPERIMENTAL PROCEDURE, RESULTS AND DISCUSSION

3. 1 Fuel Cell Tests

During this report period, the emphasis continued to be on obtain-

ing optimum fuel cell performance.

performed with the C200B membrane and with American Cyanamid Type AA- 1

electrodes in the Astropower standard (analytical) fuel and the compact

fuel cell design") are compiled in Tables I and 11, respectively. Tables III,

V and VI depict the various experiments performed in the analytical fuel cell

involving different types of catalyst-electrode configurations.

The results of the most significant tes ts

All tests were performed at a constant current density of 30 2 ma/cm . The results obtained a re discussed below.

It is to be noted that fuel cell resistance listed in Tables I - VI

inclusive, had been calculated from the slopes of the straight portions of the

cor responding polarization curves. Essentially, they represent the ohmic

resistance for the cell at that particular point of the test.

3. 1 . 1 Standard Fuel Cell Tests

Test ( l) , continued from the previous quarterly period, (2)

was performed at 25OC in order to establish the effect of temperature and

membrane thickness on performance.

category as well, The plots of Figures 1 and 2 compare both the cell voltages

and fuel cell resistances a s obtained from polarization curves of Test (1) with

corresponding values obtained previously for a similar membrane at 65 C ,

(Test 5 , Table I). (') Evidently, a s temperature increases from 25 C to

65 C, fuel cell performance improves. As described previously, we conclude

that the higher fuel cell resistance at 25 C is due to inadequate product water

removal resulting from lower vaporization at this temperature.

waterproofing at the membrane- electrode interface should improve the perform-

ance at that temperature.

ional feasibility a t 25OC for the C200B membrane,

thickness is concerned, membrane thickness in the range of 0.50 to 0. 75 mm does

does not appear to affect fuel cell performance.

Tests (6), (7) and (8) a re in the same

0

0

0

0

Additional

However, Test (1) does demonstrate stable operat-

As far a s the membrane

(1)

It was shown in Reference 1 that optimum performance

SM- 4622 1-Q4 4

L

I occurred within the temperature range of 65O to 120°C. Hence, fuel cell

tests were performed at 65 C in further efforts to ascertain the maximum

possible level of performance.

0

Test (2) was run with platinum black impregnated in

the membrane to the extent of one-third the thickness of the membrane, as

described in Reference 1.

third layers was 2Wo by weight and the middle layer was comprised of C200B

material alone.

which is about 1470 of the total membrane weight. Actually, Test (2) concludes

the study conducted at 65 C, described in Reference 1, wherein the concentrat-

ion of platinum black in the outer one-third layers of the membrane was

varied from 10% up to 4070 by weight.

Figures 3 and 4.

corresponding resistance- time curves a r e given in Figure 4.

indicate that in the case of 10% platinum black impregnation, poorer perform-

ance results, whereas performance remains essentially constant over the

20 to 4070 range.

third layers of the C200B membrane did not afford significantly higher perform-

ance than the untreated membranes at 6SoC, (') it accounts for stable and

essentially constant performance at temperatures as high a s 15 l0C. To date

untreated C200B membranes have manifested favorable fuel cell performance

levels at temperatures higher than 7SoC, which have been of shorter duration.

The concentration of platinum in both outer one-

This amounts to about 0.5 grams platinum per membrane

0

The results a r e summarized in

In Figure 3 the voltage-time curves a r e plotted and the

Both plots

Although impregnating platinum black into the outer one-

In Reference 1 it was &served that the active zrea for

electrocatalysis appears to be at the surface of the membrane only.

result, the membrane used in Test (3) had been impregnated only to the extent

of about 5% on both sides, with ZO%o platinum black by weight, leaving the

middle 90% layer with nonimpregnated C200B material. This amounts to

about 0 .07 grams of platinum per membrane which is about 2% of the total

membrane weight.

porated in the two outer one-twentieth layers containing Z ~ O by weight of

platinum black.

adding the 270 Teflon waterproofing agent.

at 25OC in order to ascertain whether the additional amount of waterproofing

agent enhances performance at that temperature.

further whether fuel cell performance varied over the temperature range of

As a

Test (4) was performed with 270 Teflon by weight incor-

No significant performance improvement was observed by

This experiment will be attempted

Test (6) was run to determine

SM- 4622 1 - Q4 5

65O to 12OoC; it had Teflon incorporated into the system as well.

test only a fine spray, resulting in a light surface coating, was administered

to the membrane surface.

at 3OO0C prior to the test.

stable performance is possible for this membrane system over the tempera-

ture cycle of 650 to 102O and back to 65OC. Teflon contributes to the stability

in performance.

In this

The composite membrane sandwich was re- sintered

The results of this test indicate that constant,

Test (5) w a s the first attempt to incorporate back-up

plates with 136 holes and groove width of 0. 105 inch in the old (analytical) fuel

cell. Although the initial performance looked good and a high performance was

expected, the nature of the "Zeolon-H" as supplied by the Norton Company

resulted in significantly weaker membrane structures and consequently, poor

fuel cell performance. This matter was discussed in Reference 3. 0 0 Tests (7) and (8) were run at 70 C and 151 C , respect-

ively.

the C200B membrane impregnated with platinum black to the extent of 20%

in the outer one-twentieth layers, (0.07 grams platinum per membrane) at

elevated temperatures.

Tests (7) and (8) a r e similar, demonstrating that fuel cell performance does

not vary with temperature in the range of 65O to 151OC.

Reference 1, the constancy of performance with increase in temperature of

the Astropower inorganic membrane fuel cell is due to the invariance of the

The purpose of both tests was to observe the fuel cell performances of

Resistances obtained from polarization curves in

As discussed in

. . .I AvII~c r\n cond~acti-~viity ef the m e m 5 r a ~ e with rise i.r temperature, at least to any

significant extent.

15 l0C.

Electrode kinetics do not appear to be controlling up to

Polarization curves for Tests (2), (3), (4), (6), (7) and

(8) a r e given in Figures 5 through 10.

3.1.2 Compact Fuel Cell Life Tests

Most of the work done with the Astropower compact

fuel cell involved two units requiring a two-inch diameter membrane.

design can be seen in Figure 3, Reference 1.

depicting the most significant results a r e given in Table II. This fuel cell was

designed using mass and heat transfer analysis and engineering experience, a s

discussed in Reference 1.

This

The results obtained for tests

SM-46221-Q4 6

The purpose of Test (9) was to determine whether contact

resistance between electrode and backup plate could be decreased by the gold-

surfacing of the stainless steel backup plate. This was done by a commercial

electrodeposition process which provided a gold deposit 5.0 x

inch thick.

occurs.

5 to 10.0 x 10-

The results of Test (9) show that no enhancement in performance

It was shown in Reference 1 that the free gas space and

the number of holes in the backup plate were directly related.

that point, it would be expected that increased free gas space should lead to

more reaction sites and consequently better performance, provided the amount

of metal to metal contact between electrode and backup plate is not substantially

reduced.

one- eighth inch diameter holes with groove widths of one- eighth inch.

ently, in Test ( lo) , there is no enhancement over the previous optimum perform-

ance which used backup plates with 96 similarly sized holes, because in order

to provide for more holes in the backup plates, it was necessary to reduce the

size of the contact areas (lugs) on the electrode side of the backup plates.

the next step was to increase the metal to metal contact between the backup plate

and electrode, and yet retain the 136 one-eighth inch diameter holes. To accom-

plish this, the electrode side of the backup plates was modified by decreasing the

channel groove width from 0. 125 to 0.105 inch. Figure 11 shows how this modi-

fication increases the lug size. Figure 13 shows the cr isscross arrangement of

channel grooves on the electrode facing side for the three types of backup plates,

eachwith a different niirnber of holes - The alignments of grooves and lugs a r e apparent.

As indicated at

A s a result, Test (10) was performed with backup plates having 136

Appar-

Hence,

Test 11 involved the use of this apparently improved

backup plate modification.

to date in the program. Correspondingly, periodic polarization curves gave the

lowest fuel cell resistances (0. 18 to 0.20 ohms) obtained to date. Figure 14

shows an extension of the plot originally given in Reference 1, describing the

relationship between gas exposed area and backup plate design. Hence, i f both

gas exposed area and lug contact area a re maximized simultaneously, the best

possible performance for this type of configuration should result. Figure 15

relates gas exposedarea and the lowest fuel cell resistance obtainedfor eachbackup

plate shown in Figure 14.

optimum g a s exposed area and lug-contact a rea a r e being approached. Figure 16

The level of performance was the highest obtained

The flattening out of the curve indicates that the

SM-4622 1-Q4 7

shows the impression that the backup plate contact lugs make with the AA- 1 Type,

American Cyanamid electrode. It can be seen that the a rea exposed to the gas is

considerable, while the electrical contact points a r e evenly distributed.

The purpose of Test (12) was to compare the performance

of the fuel cell when the electrical leads were connected to projecting tabs cut

out of the American Cyanamid AA- 1 electrodes.

a r e connected to the backup plates.

in Figure 23, the tabs offer considerably higher resistance than do the backup

plates.

ccjntributes to this enhanced resistance.

Ordinarily, the electrical leads

As can be seen from the polarization curves

It is quite possible that the IR drop laterally across the electrodes

With a promising start , it was thought that Test (13)

would duplicate the maximum performancep but the cell performance diminished

Considerably after 104 hours.

could be the result of irregular "Zeolon-H" received from the vendor which

caused significantly weaker membranes.

As mentioned previously in Test (5), the failure

Tests (14) and (15) were both evaluated in a large dia-

This unit is meter compact fuel cell using a four-inch diameter membrane.

shown in Figure 19. Test (14) used a C200B membrane with no special treat-

ment while Test (15) had a C200B membrane impregnated with platinum black

to the extent of 20% in the outer one-twentieth layers. It was believed that the

relatively low current density obtained in Test (14) after 74 hours of operation

at 65 C was due to inadequate distribution of reactant gases over the entire

area of the backup plate.

both compartments in Test (15), a s illustrated in Figure 18.

density of 30 ma/cm , comparable results were obtained in Test (15) a s in

the two-inch standard o r compact fuel cell tests. This demonstrates that a

four-fold increase in the area has little o r no effect on the fuel cell perform-

ance.

( l l ) , (12), (14) and (15).

0

Therefore, g a s diffusor plates were installed in

At a current 2

Figures 20 through 25 a r e polarization curves for Tests (9), ( lo) ,

Experiments involving a wicking arrangement using

cellulosic felt a r e being continued and the results a r e being analyzed.

A complete description of this work will be presented in ensuing reports.

SM-4622 1-04 8

.

3.1.3 Fuel Cell Tests with Palladium and Indium Catalyst Material

Tests were performed in the analytical fuel cell with

C200La ta lys t composite membranes prepared as described in Reference 1.

These membranes consisted of three layers of compressed material. The

two outer layers were composed of mixtures of C200B membrane material

and catalyst; the center section consisted of C200B material alone. In this

study, the effectiveness of 50/50 platinum-palladium black mixtures simul-

taneously on both the hydrogen and oxygen sides, 50/50 platinum-iridium black

mixtures on the hydrogen side only, and 50/50 silver-palladium black mixtures

on the oxygen side only were determined. The workwas performed with American-

Cyanamid Type AA-1 electrodes, the standard for fuel cell tests on this

program.

cm ) were sprinkled on each side of the membrane during the electrode-

membrane assembling.

Additional quantities of the appropriate catalyst mixture (0. 025 g / 2

The results obtained a re summarized in Table III. Noteworthy perfo rmance was obtained for the 50/50 platinum-palladium

catalyst mixture (Tests 16 and 17).

membrane system, as determined from polarization data, is less than that

obtained when either platinum o r palladium catalysts a r e used separately.

This is indicated by the summary of resistances obtained from fuel cell studies

performed under comparable conditions given in Table IV.

the 50/ 50 platinum-palladium catalyst combination merits further study.

The fuel cell resistance of this catalyst-

The capability of

Referring back to Table ILI, it is evident that the

platinum-iridium catalyst combination on the hydrogen side and the silver-

palladium combination for the oxygen electrode show no promise for this

application.

3. 1.4 Fuel Cell Tests with Various Types of Tantalum and Stainless Screen Electrodes

The purpose of this effort was to ascertain the relative

merits of tantalum electrodes having platinum incorporated by electrodeposi-

tion, paste and sintering techniques. In addition, i t was desired to ascertain

the effects of varying amounts of Teflon and silicone waterproofing agents.

Fifty mesh tantalum screens were used throughout this study.

SM-46221 -Q4 9

Electrodeposition was carried out in 370 H2PtC16 (aq).

Up to 40% (by weight of screen) of platinum was deposited in this fashion.

pastes consisted of platinum black suspended in a toluene solution of silicone

resin (G.E. SR-224).

was evaporated and the resin was cured at 9OoC. made of platinum black in aqueous Teflon suspension.

were prepared in the following manner. First, a thin film of platinum black

was electrodeposited on the tantalum screen from 3% H2PtC16 (aq). solution.

Then, the screens were subjected to three o r four sintering cycles in which

they were successively immersed in an aqueous suspension of Teflon, dusted

with finely divided platinum black, lightly pressed between two sheets of

aluminum foil, and sintered for two minutes at 35OoC.

contained in the finished electrodes was estimated to be 570 by weight.

concentration of platinum was varied from 15 mg/cm2 up to 30 mg/cm .

The

After application of the paste to the screen, the toluene

In addition, pastes were

Sintered electrodes

The amount of Teflon

The 2

The results obtained with the standard C200B membrane

a re summarized in Table V and the results obtained with the C200B-platinum

impregnated membranes a re summarized in Table VI. evident i n Table V, i. e. ,

Certain trends a r e

(a) The different techniques for platinum catalyst

impregnation a r e essentially equally effective.

(Similar conclusions were reached by General Electric. ) (4)

(b) Increasing amounts of platinum catalyst up to as

high as 20 to 30 mg/cm2 a re conducive to improved

fuel cell performance.

(c) Silicones appear to be as effective as Teflon as waterproofing agents.

The results of Table VI indicate that the above trends

a re applicable as well.

as 40 mg/cm2 is deleterious to fuel cell performance.

range for platinum loading i s 20 to 30 mg/cm . determined at the present time.

various experimental electrode screens indicated a considerable decrease in

In addition, it appears that a platinum loading as high

Possibly, the optimum 2 This matter is being

Optical transmission measurements on the

SM-46221 -Q4 10

2 electrode porosity when the catalyst loading was as high as 40 mg/cm

reasonably good performance was obtained with the stainless steel electrode

screen (Test 31) in this initial exploratory study, merits further attention

since stainless steel i s considerably less expensive and more readily available

than platinum black.

That

3.1.5 Fuel Cell Tests with Unitized Membrane-Catalyst- Electrode Structures

Two types of structures have been prepared and evaluated

i n a fuel cell, without particularly worthwhile results being achieved in either

case.

palladium and tantalum in their resinate solutions have been silk screened on

the surfaces of platinum-impregnated membrane composites both before and

after their final sintering (referred to as diffusion bonding in Reference 1).

Then, theentire assembly was fired to bond the electrode layers to the catalyst-

membrane compo sit e.

In one type of structure, electrode materials such as platinum,

Figure 26 is a photograph of the front view of such a

configuration.

obtained when the usual platinum-Teflon-tantalum screen gas diffusion electrode

was returned to the same fuel cell in one particular experiment, indicates that

adequate electrocatalysis was not achieved by the silk screening approach.

The fact that significant improvement in performance was

In the second approach the waterproofed, platinized

tantalum screen electrode, together with its tantalum leads were pressed and

sintered directly into the membrane structure.

backup plates acting as a support for the unitized structure.

this structure is Figure 27.

and electrode is a requirement f o r the proper functioning of the inorganic

membrane fuel cell.

The system was used with

A photograph of

Possibly, a distinct interface between membrane

The best results achieved with this type of membrane-

catalyst-electrode structure to date have been 1 ma/cm2 at 0. 3 volts and

65OC. This matter will be given further attention.

SM-46221 -Q4 11

4 . 0 FUTURE WORK

(1) The study of catalyst-membrane composites and electrode- catalyst- membrane composites according to the plan given in Reference 1 will be com-

pleted.

catalyst mixture incorporated in both the membrane and porous electrode

structure . (2) Ruthenium and rhodium wi l l be investigated as catalyst material.

(3) The aspect of ohmic resistance contribution to electrode polariza-

Particular attention will be given to the 50/50 platinum-palladium

tion will be determined by current-interruptor experiments.

correlated with previously determined membrane resistivities at 1000 cps.

Efforts will be made to minimize contact resistance to the fullest extent.

This will be

(4) The influence of wicking arrangements on fuel cell performance will be established.

SM- 4 62 2 1 - Q4 12

5.0 REFERENCES

"Inorganic Ion Exchange Membrane Fuel Cell, I ' NASA- Lewis

Research Center Contract NAS 3- 6000, Quarterly Progress

Report SM-46221-Q3, Period Ending 10 April 1965.

Ibid. , Quarterly Progress Report SM-4622LQ2, Period Ending

10 January 1965.

Ibid., Monthly Progress Report for Period Ending 10 June 1965.

Report SM-46221- h4ll.

"Research on Low Temperature Fuel Cell Systems, Contract

DA- 44- 009-Eng- 3771, U. S. Army Research and Development

Laboratories, Ft. Belvoir, Virginia, 1961.

SM- 46221-44 13

c

6 . 0 PROJECT PERSONNEL

The following Astropower staff personnel w e r e connected with

the program during the reporting period.

Dr . C. Berger

D r . M. P. Strier

Mr. F. C . Arrance

Mr. G. Belfort

Mr. A. G. Rosa

Mr. R. Hubata

Mr. R. Rahe

Mr. J . Armantrout

Mr. P. VanSchenck

Principal Investigator

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Side View

Top View

a. Groove Width Same as b. Groove Width Smaller Hole Diameter Than Hole Diameter

Figure 11. Comparison of Different Layouts of Grooves and Holes for the Electrode Facing Side of the Backup Plates

25

(a) Forty-Four holes, 1/8 inch in diameter, in stainless steel backup plate

(b) Ninety-six holes, 1/8 inch in diameter, in stainless steel'backup plate

(c) One hundred and thirty-six holes, 1/8 inch in diameter, in stainless steel backcp plate

Figure 12. From Left to Right: Three Types of Backup Plates Used in Astropower Compact Fuel Cell (Gas Compartment Face)

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(a) Forty-four holes, 1/8 inch in diameter, in stainless steel backup plate

(b) Ninety-six holes, 1/8 inch in diameter, in stainless steel backup plate

(c) One hundred and thirty- six holes , 1/ 8 inch in diameter, in stainless steel backup plate

Figure 13. From Left to Right: Three Types of Backup Plates Used in Astropower Compact Fuel Cell (Electrode Face)

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Figure 15. Relationship of Fuel Cell Resistance with Available Electrode Area Exposed to the Reactant G a s e s

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b

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dark area- exposed to gas

light grey area - contact points for electrical lead off and to maintain equal pressure against the electrode -membrane composite

Figure 16. Two-Inch Diameter American Cyanamid AA-1 Electrode and Platinum Black Deposit, Showing the Contact Points, Resulting from the Lugs of the Back-up Plate

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C C B - B - American Cyanamid Type A A-1 Electrode Tabs

Figure 17: Inorganic Ion Exchange Membrane Backup Plate Sandwich, Illustrating FJectrical. Lead Off Via (a) Backup Plates (b) Electrode Tabs.

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Figure 19. Large Astropower Compact Fuel Cell

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Figure 27. Unitized, Fused C200B Membrane-Electrode Configuration, Demonstrating Silver Wire Leads Interwoven Through Electrode Screen Structure

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. TABLE N

COMPARISON OF RESISTANCE AT 65t2OC AND VARIOUS TIME INTERVALS FOR 20 PERCENT PLATINUM AND PALLADIUM BLACK

CATALYST AND A 50/50 RATIO OF PLATINUM TO PALLADIUM-BLACK CATALYST IMPREGNATED IN THE OUTER

ONE-THIRD LAYERS

Resistance (OHMS) at 65 22OC

Time (Hours) Catalyst

Yo R. 20

% Pd. 20 -

0-30 30-40 40-50 50-60 60-70 70-80

Test No. -37 .40 --- -- - -(a) .34 - - -

(b) -41 -- - .33 .33 - - - .35

Yo( 5 O/ 5 0)Pt. / Pd. 20 16 -27 - - - .25 - -- . 25 ---

(a) From Reference 1 - Fuel Cell Test No. 19 and 23

(b) From Reference 1 - Fuel Cell Test No. 20

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