the electrochemical reduction of fumaric acid on hg-bi

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1972

The electrochemical reduction of fumaric acid on Hg-Bi cathodes The electrochemical reduction of fumaric acid on Hg-Bi cathodes

Chen Hwei Chi

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THE ELECTROCHEMICAL REDUCTION OF FUMARIC

ACID ON Hg-Bi CATHODES

by

Chen Hwei Chi, 1941-

A DISSERTATION

Presented to the Faculty of the Graduate School of the

UNIVERSITY OF MISSOURI-ROLLA

·'·

In Partial Fulfi~.lment of the RequirerneJ\~ for the Degree

DOCTOR OF PHILOSOPHY

in

CHEMICAL ENGINEERING

1972

T2631 83 pages c.l

ii

PUBLICATION THESIS OPTION

This dissertation has been prepared in the style

utilized by the Journal of the Electrochemical Society.

Pages 1 through 45 will be submitted for publication in

that journal. Appendices A to E have been added for

purposes normal to thesis writing.

iii

ACKNOWLEDGEMENTS

The author wishes to thank Dr. J.W. Johnson, Pro

fessor of Chemical Engineering, who served as research

advisor, and Dr. W.J. James, Professor of Chemistry and

Director of the Graduate Center for Material Research.

Their help, guidance, and encouragement are sincerely

appreciated.

A further word of appreciation is extended to the

Graduate Center for the use of equipment and a research

scholarship.

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS • • • iii

TABLE OF CONTENTS iv

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . v

LIST OF TABLES • • . . . . . . . . . . . . THE ELECTROCHEMICAL REDUCTION OF FUMARIC ACID ON

Hg-Bi CATHODES • • • • • • •

Abstract .•.

Introduction •

Experimental

Results and Discussion

Bibliography

Captions for Figures

APPENDICES . • . •

A. Materials

B. Apparatus . . . . . . c. Sample Calculations for Fumaric Acid

Dissociation • • • • . • • . . •

D. Experimental Data •

E. A Micro-Determination of Succinic Acid

. • viii

1

1

1

3

5

21

23

46

46

47

48

50

69

VITA . • • . • • . • • · • • • • • • • • . • • . . . . 72

v

LIST OF FIGURES

Figure Page

1 Polarization curves for the cathodic

reduction of fumaric acid on Hg at 60°C in

2 Polarization curves for the cathodic reduc-

tion of fumaric acid on Hg/l%Bi at 60°C

3 Polarization curves for the cathodic reduc

tion of fumaric acid on Bi at 60°C in


tion of 0.03 M fumaric acid on Hg at 60°C

5 Polarization curves for the cathodic

reduction of 0.03 M Fumaric acid on Hg/l%Bi

at 60°C .


tion of 0.03 M Fumaric acid on Bi at 60°C

7 Effect of fumaric acid concentration on

current for the cathodic reduction of fumaric

acid at 60°C in 1 N H2so4 •

27

28

29

30

31

32

33

vi

LIST OF FIGURES (Con't)

Figure Page

8 Effect of the product of the undissociated

fumaric acid and H+ concentrations on

current for the cathodic reduction of

0 fumaric acid at 60 C . •

9 Arrhenius plots for the cathodic reduction of

0.03 M fumaric acid on Hg at 60°C in 1 N H2so4

(pH = 0.03)

10 Cyclic current-potential curves for 0.003 M

fumaric acid on Hg at 60°C in 1 N H2so4 (pH =

0. 3)

11 Linear relationships between peak current and

square root of sweep-rate for 0.003 M fumaric

acid at 60°C in 1 N H2so4 (pH = 0.3}

12 Linear relationships between peak current and

fumaric acid concentration from 50 mv/sec

34

35

36

37

cathodic sweep at 60°C in 1 N H2so4 (pH= 0.3) 38

13 Variation of peak potential with sweep-rate

for 0.003 M fumaric acid at 60°C in 1 N H2so4

14

(pH = 0. 3) • . • • • • • • • • •

Variation of peak current with (V - E0 ) for p

0.003 M fumaric acid at 60°C in 1 N H2so4

(pH = 0.3) ••••••••••

39

40

vii

LIST OF FIGURES (Con't)

Figure Page

15 Current-potential curves from 50 V/sec

cathodic sweep on Hg at 60°C in 1 N H2so4

(pH = 0 • 3} • • • • • • • • • • • • • •

16 Dependence of surface charges on sweep-rate

for 0.0003 M fumaric acid at 60°C in

1 N H2so4 (pH = 0.3) ...•.........

17 Fractional coverage-potential relationships

for fumaric acid from 50 V/sec cathodic

41

42

sweep on Hg at 60°C in 1 N H2so4 (pH = 0.3). 43


for fumaric acid from 50 V/sec cathodic sweep

on Hg/l%Bi at 60°C in 1 N H2so4 (pH = 0.3) 44



on Bi at 60°C in 1 N H2so4 (pH = 0.3) 45

Table

I

LIST OF TABLES

Efficiencies for the Cathodic Reduction

of 0.03 M Fumaric Acid to Succinic Acid

at 60°C .

II Rest Potentials and Tafel Slopes for

Fumaric Acid reduction-at 60°c ....

viii

Page

6

7

III Apparent Activation Energies for the Cathodic

Reduction of 0.03 M Fumaric Acid in 1 N H2so4 11

IV Results for 0.003 M Fumaric Acid During

Cathodic Sweep at a Rate of SO rnV/sec at

60°C in 1 N H2so4 (pH = 0.3)

V Comparison of Kinetic Parameters for the

Cathodic Reduction of Fumaric and Maleic

Acids .

VI Degree of Dissociation of Fumaric Acid

VII Current-Potential Relationships for the

Cathodic Reduction of Fumaric Acid on Hg at

60°C in 1 N H2so4 (pH = 0.3)

VIII Current-Potential Relationships for the

Cathodic Reduction of Fumaric Acid on Hg/l%Bi

14

20

49

51

at 60°C in 1 N H2so4 (pH = 0.3) . • . • • 53

LIST OF TABLES (Continued)

Table

IX Current-Potential Relationships for the

Cathodic Reduction of Fumaric Acid on Bi at

X Current-Potential Relationships for the

Cathodic Reduction of 0.03 M Fumaric Acid

0 on Hg at 60 C . . . .

XI Current-Potential Relationships for the


on Hg/l%Bi at 60°C

XII Current-Potential Relationships for the

XIII


on Bi at 60°C .

Current-Potential Relationships for Hydro

gen Evolution on Hg and Bi at 60°C in

XIV Current-Temperature Relationships for the


on Hg in 1 N H2 so4 (pH = 0.3)

XV current-Temperature Relationships for the


on Hg/l%Bi in 1 N H2so4 (pH= 0.3)

ix

Page

54

55

56

57

58

59

60

Table

XVI

XVII

XVIII


Current-Temperature Relationships for the


on Bi in 1 N H2so4 (pH= 0.3) ...•••

Peak Current-Peak Potential Relationships

from Cathodic Sweeps for Fumaric Acid on

Hg at 60°C in 1 N H2so4 (pH = 0.3) .•.

Peak Current-Peak Potential Relationships


Hg/l%Bi at 60°C in 1 N H2so4 (pH= 0.3)

XIX Peak Current-Peak Potential Relationships


Bi at 60°C in 1 N H2so4 (pH= 0.3) ••

XX Surface Charge-Sweep Rate Relationships

from Cathodic Sweeps for 0.0003 M Fumaric

Acid at 60°C in 1 N H2so4 (pH = 0.3)

XXI Surface Charge-Potential Relationships

from 50 V/sec Cathodic Sweep on Hg at 60°C

X

Page

61

62

63

64

65

in 1 N H2so4 (pH = 0.3) • • • . . . • . . • . 66

XXII Surface Charge Potential Relationships from

50 V/sec Cathodic Sweeps on Hg/l%Bi at

6 0 ° C in 1 N H2SO4 (pH = 0 • 3) • • • • • • 6 7

Table

XXIII

XXIV


Surface Charge-Potential Relationships from

200 V/sec Cathodic Sweep on Bi at 60°C in

1 N H2so4 (pH= 0.3) .•..•..•.

Data for the Coulombic Efficiency Studies

of the Cathodic Reduction of Fumaric Acid

to Succinic Acid • . . • • .

xi

Page

68

71

THE ELECTROCHEMICAL REDUCTION OF FUMARIC ACID

ON Hg-Bi CATHODES

Chen Hwei Chi

Department of Chemical Engineering

and

Graduate Center for Materials Research

University of Missouri-Rolla

Rolla, Missouri U.S.A.

ABSTRACT

1

The electrochemical reduction of fumaric acid was

studied on Hg, Hg/l%Bi amalgam, and Bi at 60°C in acidic

solutions of various pH ranging from 0.3 to 3.7. The

fumaric acid was reduced to succinic acid with high

efficiency on each electrode. The steady state kinetic

parameters included Tafel slopes of ca. 2.3 RT/F and

first order concentration dependences for both undissociated

+ fumaric acid and H . Transient measurements indicated low

coverages of adsorbed fumaric acid and no adsorbed hydro-

gen species in the potential region of the reaction. A

reaction mechanism is proposed which involves a chemical

rate determining step between an adsorbed fumaric acid

molecule(that has added an electron} and a non-adsorbed H+.

INTRODUCTION

studies of the electrolytic reduction of fumaric acid

appearing in the literature have mostly concerned current

2

efficiencies and polarographic analyses. Kanakam, et

al., 1 found a current efficiency of 95 percent for the

reduction of fumaric to succinic acid at a rotating lead

cathode. Herasymenko2 reported that only undissociated

species of fumaric acid were reduced during the electro-

lyses of aqueous solutions at a dropping mercury electrode.

Schwaer, 3 Herasymenko and Tyvonuk, 4 and Vopicka5 made

extensive polarographic investigations of fumaric and

maleic acids (geometric isomers) in acidic and buffered

solutions of various pH. They found that more negative

potentials were required to reduce fumaric than maleic

acid. Kalousek6 reported that the reduction of fumaric

acid is irreversible at a dropping mercury electrode.

Elving and Teitalbaum7 proposed a reduction sequence based

on polarographic studies in which a radical ion is formed

during a reversible step and, possibly simultaneously,

acquires a proton. The further reduction included another

electron transfer and hydrogen ion addition to form

succinic acid.

An extensive study of the reduction of maleic acid on

Hg, Hg/Bi, and Bi electrodes was made by Hsieh. 8 He found

high efficiencies for the reduction to succinic acid,

independent of the cathode used. A reaction mechanism was

proposed which involved a chemical rate determining step

between an adsorbed maleic acid species which had gained

an electron and a non-adsorbed hydrogen ion.

3

Although extensive polarographic investigations of

fumaric acid reduction have been carried out, it was felt

a need existed for a thorough kinetic study to obtain

more detailed information about the reaction mechanism.

Both steady state and transient methods were employed in

the present investigation. Steady state methods were used

to evaluate such kinetic parameters as Tafel slopes,

coulombic efficiencies, pH, concentration, and temperature

effects. The transient methods were used primarily to

obtain information regarding adsorption phenomena. A com-

parison of the results of this study with those obtained

by Hsieh for maleic acid is also of interest.

EXPERIMENTAL

The electrolytes, pH 0.3 to 3.7, were prepared using

appropriate quantities of H2so4 , K2so4 , KOH, fumaric acid,

and conductivity water. The reagents were Fisher "certified"

grade. The fumaric acid concentration was varied from 0.001

to 0.03 M, the upper limit determined by the solubility.

The sulfate concentration was held constant at unit nor-

mality to insure good conductance. Matheson "prepurified"

grade nitrogen was used for purging and stirring.

Three different cathodes (Hg, Hg/l%Bi amalgam, and Bi)

were used. The Hg was Bethlehem's* triple-distilled instru

ment grade and the Bi was ESPI's** 6N grade. The amalgam

*Bethlemen Apparatus Company, Inc., Hellertown, Penn. **Electronic Space Products, Inc., Los Angeles, California

4

was prepared by dissolving an appropriate amount of Bi

in Hg with slight heating. A planar Bi electrode was

prepared by machining a flat surface on a Bi rod. The

counter electrode was a piece of platinized-Pt wire gauze.

The reference electrode, Hg/Hg2so4 (1 N H2so4 ), was con

nected to the cathode via a Luggin capillary and salt

bridge of the same electrolyte used as in the electrolysis

cell.

The cells used with the liquid cathodes (Hg and

Hgjl% Bi) were similar to those described by Hsieh. 8 A

conventional H-cell was used with the Bi cathode. The

temperature of the catholyte was maintained at the stated

values + O.S°C. The experimental procedures and equipment

for the steady state measurements have been described. 8

The transient measurements were made in a manner similar

to those of Gilman and Breiter. 9 The quantities of

succinic acid produced during the coulombic efficiency

studies were also determined as described previously. 8

5

RESULTS AND DISCUSSION

A. Coulombic Efficiency

The results of the coulombic efficiency experiments

are shown in Table 1. The efficiencies for succinic acid

production vary from 85 to 97 + 2 percent. No hydrogen

evolution was observed at the cathodes, although small

amounts could have been produced that dissolved directly

in the electrolyte without bubble formation. Gas

chromatographic (flame ionization) examination of the

electrolytes revealed no product other than succinic acid.

Thus, the predominant electrochemical reaction can be

represented as

HOOC-CH=CH-COOH(aq) + 2H+(aq) + 2e = HOOC-CH 2 -cH2-COOH(aq)

Fumaric Acid Succinic Acid

( 1)

B. Rest Potentials

The open circuit potentials with fumaric acid present

in the various electrolytes are shown in Table II. The

thermodynamic values for Eq. 1 (E0 = 0.49V) are in the

proximity of the values for Hg. However, the random

variation of the measured values with fumaric acid concen

tration and pH indicates that they cannot be attributed to

fumaric acid reduction. This is more apparent with the

TABLE I

EFFICIENCIES FOR THE CATHODIC REDUCTION OF

0.03 M FUMARIC ACID TO SUCCINIC ACID

AT 60°C

Electrode pH Ixlo 3 Efficiency

amp** Percent

Hg 0.3 1.5 95

" 2.9 1.0 85

Hg/l%Bi 0.3 4.0 97

II 2.9 2.0 86

Bi 0.3 5.0 91

II 2.9 3.0 90

*Average of a minimum of two determinations.

**The cathodic are2s were 10 cm2 for the Hg and Hg/l%Bi and 3 em for the Bi.

6

*

pH

0.3

II

II

II

II

II

1.5

2.2

2.9

3.7

7

TABLE II

REST POTENTIAL AND TAFEL SLOPES FOR FUMARIC ACID REDUCTION AT 60°C

Fumaric E rest Tafel slopes acid cone. Hg Hg/l%Bi Bi Hg Hg/l%Bi Bi

gmole/1 V,SHE V,SHE V,SHE v v v

0.594 0.215

0.0003 0.579 0.197 0.230 -0.080 -0.080

0.001 0.579 -0.075

0.003 0.591 0.205 - -0.070 -0.072 -0.066

0.01 0.582 0.225 -0.067 -0.068

0.03 0.589 0.205 0.215 -0.068 -0.068 -0.065

0.03 0.580 0.20 0.19 -0.065 -0.067 -0.067

0.03 0.585 -0.065

0.03 0.580 0.20 0.16 -0.070 -0.070 -0.070

0.03 0.598 -0.073

8

Hg/l%Bi and Bi electrodes where the rest potentials are

very near the reversible values for Bi dissolution (E0 =

0.215 V). Qualitative analyses of electrolytes that had

contacted these latter electrodes revealed the presence

of Bi+3 . The decreasing value with Bi at the higher pH's

is consistent with an oxide fiLm which forms under these

conditions.

C. Steady-State Current-Potential Relationships

Polarization curves for the various fumaric acid

concentrations and pH's are shown in Figs. 1-6. There are

three distinguishable regions in the curves: a residual

current, a linear Tafel, and a limiting current region.

The residual currents were not significantly affected by ....

fumaric acid or H concentrations but did increase when

Bi/Hg and Bi cathodes were used. Since it was found that

some Bi dissolved in the electrolytes, the increased

currents were probably due to redeposition of the Bi when

the potential was lowered. A finely divided (black)

deposit of Bi was present on the Bi cathodes after the

electrolyses. The slopes of the linear Tafel regions

were -65 to -80 mv, ca. -2.3RT/F. With Langmuir-type

adsorption, this normally indicates a slow surface chemical

reaction following the first electron transfer. Currents

in the Tafel region were reproduceablewithin 10 percent.

9

D. Concentration and pH Effects

The effect of fumaric acid on c.d. in 1 N H2so4 is

shown in Fig. 7. The plots are linear with slopes of about

one for all the cathodes. The reactive species are not

distinguished by this plot since for a given pH, the frac-

tion of fumaric acid dissociated is independent of the

initial concentration due to the low dissociation constant

-4 (K1 = 9.3 x 10 ). The data for the higher pHts where

dissociation is appreciable were correlated by a trial and

error procedure. Fig. 8 shows the most successful correla-

tion which involved the product of the unionized fumaric

acid and H+ concentrations. The slopes of these plots are

also unity. Thus, H2F* is indicated to be the reactive

fumaric acid species, and both it and H+ have a first order

concentration effect.

With this information, an empirical relationship for

the current density can be written:

(2)

This expression is valid for all the cathodes. However it

should be noted that for a given potential, the c.d. is

increased significantly** on the Hg/Bi and Bi cathodes.

*Undissociated fumine acid.

**In the linear Tafel region, isi ~ l0 3iHg·

10

E. Limiting Currents

An examination of Figs. 1-3 shows the limiting currents

to be proportional to the fumaric acid concentration. As

would be expected at the lower potentials, the h.e. begins

to make a substantial contribution to the current.

F. Temperature Effect

Arrhenius plots for the reduction of fumaric acid on

Hg are shown in Fig. 9 for various potentials within the

linear Tafel region. These plots are typical for the Hg/l%Bi

and Bi cathodes. The resulting apparent activation energies

are tabulated in Table III. The effect of potential,

aE'/aV is also shown in the table and the values agree well a '

with those predicted from Eq. 2, i.e., For 23 Kcal/volt.

The activation energies are notable due to their smallness.

Ordinarily one might associate these values with a diffusion

controlled reaction. However, this was not the case here as

there was no effect of stirring.

G. Low sweep Rate Voltamrnetry

Cyclic potential sweep measurements employing several

linear sweep rates were made for all the cathodes with

various fumaric acid concentrations. A set of typical i-V

curves are shown in Fig. 10 for 0.003 M fumaric acid in

1 N H2so4 on Hg. The observed shift of the peak potential

with sweep rate is normally associated with irreversible

TABLE III

APPARENT ACTIVATION ENGERIES FOR THE CATHODIC

REDUCTION OF 0.03 M FUMARIC ACID IN

1 N H2so4

Electrode v

Volts(SHE)

Hg -0.355

" -0.405

" -0.475

Hg/l%Bi -0.305

" -0.355

" -0.405

Bi -0.255

II -0.305

II -0.375

E' a

Kcal

7.3

6.0

4.5

7.0

5.6

4.2

5.3

4.0

2.7

aE~/av

Kcal/volt

23

28

22

11

12

reactions to which the following relations apply10- 12

5 1/2 1/2 l/2 i = 2. 85 x 10 n (an ) D C \}

p a {3)

= 0.227nFCk' exp[-(an F/RT) {V - E0 )] a P

vp = E0 - (RT/an F)]0.77- 0.5 ln(k'/D) a

+ 0.5 ln(anaF/RT)]

{ 4)

(5)

The applicability of these equations to the reduction of

fumaric acid is illustrated in Figs. 11 and 12 which show 1/2

linear plots of ip vs. \) and log ip vs. log c as

required by Eq. 3. The associated first order concentra-

tion effect is also exhibited in Fig. 12. The displacement

of the curve for Bi in Fig. 11 and its vertical shift in

Fig. 12 from the curves for Hg and Hg/l%Bi is unexpected.

As will be seen below, ana is the same for all the

cathodes, and the other terms in Eq. 3 are independent of

the cathode composition. The explanation may be associated

with the different cell geometries since these relation-

ships involve diffusion phenomena. The Hg and Hg/l%Bi

cathodes were liquid pools at the bottom of the cathodic

compartment in a vertical electrode configuration while

the solid Bi cathode was suspended vertically in the

cathodic compartment of an H-oell (see experimental) with

a horizontal electrode configuration.

13

From Eq. 5, there should exist a linear relationship

between VP and log u which has a slope of -2.3RT/2~naF.

Such a plot is shown in Fig. 13. The relationship is

linear for all three cathodes with slopes varying from

-0.066 to -0.069 v. At 60°C, 2.3RT/F = 0.068 v, thus

~ 1, or n = 1 when ~ = 0.5*. a A somewhat similar

relationship exists between VP - E0 and log ip as shown

in Eq •. 4. These plots are shown in Fig. 14** and the

resulting slope of ca. -0.135 V which corresponds to

2.3RT/~naF. Again ~na = 0.5 or na = 1. The log i intercept

from Fig. 14 (Vp - E0 = 0} can also be used to estimate the

rate constant k' in Eq. 4. These values are shown in Table

IV along with a summary of other data from this section

as well as calculated peak currents*** from Eq. 3.

The ability of Eqs. 3-5 to correlate data in this

section is evidence for the irreversibility of the cathodic

reduction of fumaric acid (as previously report by Kalousek6 )

and the value na = 1 indicates that one electron is trans

ferred during or prior to the r.d.s.

* The value normally assigned to ~.

** The standard potential E0 used above was estimated from thermodynamic data to be 0.49 v.

*** The diffusion coefficient D = 5.4 x 10-5 cm2/sec used in this calculation was determined from the Stokes-Einstein equations.l3

TABLE IV

RESULTS FOR 0.003 M FUMARIC ACID DURING CATHODIC SWEEP

AT A RATE OF 50 rnV/SEC AT 60°C IN 1 N H2so4

(pH = 0.3}

Slope Slope Electrode V vs. log V (V -E0 }vs. i n i* p,t i** p p p a p,e

Volts Volts rna rna

Hg -0.068 -0.135 1 19 12 ,;]5

Hg/l%Bi -0.066 -0.132 1 19 10.5

Bi -0.069 -0.142 1 5.7 9.6

k'

em/sec

4.7xlo-15

4.7xlo-12

l.lxlO -9

*Theoretical value of i evaluated from Eq. 3, the cathodic areas were 10 cm2 for the HgPand Hg/l%Bi and 3 crn2 for the Bi.

**Experimental value of ip. f-1 ~

15

H. Adsorption Characteristics

The method used to determine the coverages of reactive

species on the cathodes employed fast sweep rate voltammetry

described by earlier workers. 9 • 14 i-V curves for a sweep

rate of 50 V/sec in 1 N H2so4 with and without fumaric acid

present are shown in Fig. 15. The difference Q in the

amount of charge passed during the two sweeps (area between

the curves) is generally a function of sweep-rate u. How-

ever, under favorable conditions, a plateau may be observed

where Q is relatively independent of u and can be related to

the amount of adsorbed reactive species. Values of Q were

determined for several sweep-rates for the three cathodes

used in this study and are plotted vs. u in Fig. 16. A

short plateau can be seen in all three instances at about

50 V/sec for Hg and Hg/l%Bi and 200 V/sec for Bi*. Further

studies were made at these sweep-rates for various fumaric

acid concentrations and initial cathodic potentials. The

results of these measurements are shown in Figs. 17-19 where

Q has been converted to a fractional coverage e by dividing

by Qm' the charge necessary to reduce a complete monolayer

of fumaric acid. Q was estimated to be 65 ~c/cm2 assuming m

that (1) two electrons are required for each fumaric acid

molecule and (2) the fumaric acid molecule lies flat on

f d . of 49 o 2,15 the electrode sur ace an occup1es an area A • It

*The higher sweep-rate for the plateau with Bi indicates the reaction ctccurs faster on this surface, in agreement with steady-state observations.

should be noted that if the fumaric acid molecule does

not lie flat on the electrode surface, Q will increase m

16

and the fractional coverage will be even lower than shown.

An inspection of Figs. 17-19 shows a region where

coverage is independent of potential. This corresponds to

the residual current region mentioned in the steady-state

section (see Figs. 1-3). This is a potential where very

little (relatively speaking) fumaric acid is removed by

reaction. As the potential is lowered, the rate of fumaric

acid reduction increases significantly and the coverage

decreases. At potentials of ca. -0.4 to -0.5 v, the

coverages have dropped to almost zero which corresponds to

the beginning of the diffusion-controlled regions. The

initial coverages are sufficiently low that Langmuir-type

adsorption can be assumed.

To determine whether or not adsorbed H atoms might

be participating in the reaction by H+ discharge, a back

ward (anodic) sweep technique was used which was started

at various potentials along the polarization curves shown

in Figs. 1-3. Only when the sweeps were begun at potentials

lower than -0.9 V were there any indications of adsorbed

species that could be anodically oxidized. This indicated

the absence of a•(ads) over the activation controlled

region for fumaric acid reduction.

17

I. Proposed Reaction Sequence

The following is a summary of parameters and character

istics that can be associated with the fumaric acid reduc-

tion:

is:

(1) The Tafel slope, 3V/3 log i ~ -0.068 V, indicates

a rate determining chemical step subsequent to

the first electron transfer.

(2) The reactive species is undissociated fumaric

acid and the concentration effect,

a log i/3 log CH F' is one. 2

(3) The pH effect, a log i/3H+, is one.

(4) The elctrons are transferred directly to the

fumaric acid species since they are adsorbed on

the electrode surface. Apparently no H+ is

discharged, thus the reactive hydrogen species

are protons.

(5) The low coverages of fumaric acid allow Langmuir

type adsorption to be assumed.

A reaction sequence consistent with these observations

(6)

(7)

18

This sequence leads to a rate equation that is identical

to Eq. 2, the empirical relationship.

J. Comparison of Fumaric and Maleic Acid Reduction

Both fumaric and maleic acid are reduced to succinic

acid with high efficiency. The polarization curves are

similar, containing linear Tafel regions with slopes of

c.a. -2.3RT/F. The transform, fumaric, is reduced at

potentials slightly more negative than the cis-form, maleic.

The exchange currents for fumaric acid on Hg are lo-17 to

-19 2 10 amp/em . The corresponding values for maleic acid

are lo-18 to lo-20 amp/cm2 . In both cases, the reactive

species are the unionized acids which exhibit first order

concentration effects. The concentration effect for H+ is

also first order. The activation energies for the reac-

tions are about the same. A comparison of the kinetic para-

meters are shown in Table V. All these indicate that the

same activated complex is probably formed during the

reduction sequence. Some cyclic voltammetry studies with

maleic acid on Hg were carried out in order to compare its

adsorption characteristics with the present work. The

results indicated that both acids give approximately the

same coverages of adsorbed species. In summary, it appears

that the structural differences between fumaric and maleic

19

acids do, not appreciably affect the reduction mechanism

on Hg-Bi cathodes.

20

TABLE V

COMPARISON OF KINETIC PARAMETERS FOR THE CATHODIC

REDUCTION OF FUMARIC AND MALEIC ACIDS

Efficiency (percent)

Tafel Slope (mv)

Acid Cone. Effect

pH Effect

Reactive Specie

aE'/aV(Kcal/volt) a

.o* 2 1 (amp/em )

*On Hg cathode

Maleic Acid

86-102

-2. 3RT/F

1

-1

unionized acid

"'='28

10-18 - 10-20

Fumaric Acid

85-97

-2. 3RT/F

1

-1

unionized acid

"'='23

10-17 - 10-19

21

:J?IBLIOGRAPHY

1. R. Kanakam, M.S. Pathy and H.V.K. Udupa, Electrochirn.

Acta., 12, 329 (1967).

2. P. Herasyrnenko, z. Elektrochern. angew. Physik. Chern.,

34, 74 (1928).

3. L. Schwaer, Collection Czechoslov. Chern. Commun., lr

326 (1935).

4. P. Herasymenko and z. Tyvonuk, Collection Czechoslov.

Chern. Cornrnun., ~' 77 (1930).

5. E. Vopicka, Collection Czechoslov. Chern. Cornmun., ~'

349 (1936).

6. M. Kalousek, Chern. Listy, 40, 149 (1946).

7. P.J. Elving and c. Teitelbaum, J. Arner. Chern. Soc.,

71, 3916 (1949) 0

B. S.Y. Hsieh, "The Cathodic Reduction of Maleic Acid",

Ph.D. Dissertation, University of Missouri-Rolla~l970).

9. s. Gilman and M.W. Breiter, J. Electrochern. Soc.,

109, 1009 (1962).

10. p. Delahay, J. Amer. Chern. Soc., 7 5, 1190 (195 3) •

11. P. Delahay, "New Instrumental Methods in Electro

chemistry", Interscience Publishers, Inc., New

York (1966).

12. c. Wagner, J. Meth. Phys., 32, 289 (1954).

22

13. R.B. Bird, "Transport Phenomena", John Wiley & Sons,

Inc., New York(l966).

14. M.W. Breiter and s. Gilman, J. Electrochem. Soc.,

109' 622 (1962).

15. R.W.G. Wyckoff, "Crystal Structures", Vol. 5, Inter

science Publishers, New York (1966).

23

CAPTIONS FOR FIGURES

Figure 1. Polarization curves for the cathodic reduction

of fumaric acid on Hg at 60°C in 1 N H2so4

(pH= 0.3) •. (Q, 0.03M;6, 0.01MJ0, 0.003M;

~, 0.001 M;<>, 0.0003 M; e, no fumaric acid)


of fumaric acid on Hg/1%Bi at 60°C in 1 N H2so4

(pH = 0 • 3) • ( 0 , 0 • 0 3 M; f),. , 0 • 0 0 3 M; 0 , 0 • 0 0 0 3 M)


of fumaric acid on Bi at 60°C in 1 N H2so4 (pH =

0 • 3 ) • ( 0 , 0 • 0 3 M J f),. , 0 • 0 1 M; 0 , 0 • 0 0 3 M; e , no

fumaric acid)


of 0.03 M fumaric acid on Hg at 60°c. ( Q, pH =

0. 3; f),. 1 pH = 1. 5; 0, pH = 2. 2; ~~ pH = 2. 9;

<>, pH = 3. 7)

Figure 5. Polarization curves for the cathodic reduction of

0. 03 M fumaric acid on Hg/1%Bi at 60°C. ( 0, pH =

0. 3 J f),., pH = 1. 5; 0, pH = 2. 9)

Figure 6. Polarization curves for the cathodic reduction of

0.03 M fumaric acid on Bi at 60°c. ( Q, pH= 0.3;

D,. , pH = 1. 5 1 0 1 pH 1111 2 • 9 )

24

CAPTIONS FOR FIGURES (Con 1 t)

Figure 7. Effect of fumaric acid concentration on current

for the cathodic reduction of fumaric acid at

60°C in 1 N H2so4 • ( Q, Hg cathode, -0.48 V;

~~ Hg/l%Bi, =0.38 V; 0, Bi, -0.28 V)

Figure 8. Effect of the product of the undissociated fumaric

acid and H+ concentration on current for the

cathodic reduction of fumaric acid at 60°C.

( 0 1 Hg cathode, -0.48 V; 6,, Hg/l%Bi, -0.38 V;

0 1 Bi, -0.28 V)

Figure 9. Arrhenius plots for the cathodic reduction of 0.03M

fumaric acid on Hg at 60°C in 1 N H2so4 (pH= 0.3).

( 0 1 -0.475 V; 6, -0.405 V; 0, -0.355 V)

Figure 10. Cyclic current-potential curves for 0.003 M fumaric

acid on Hg at 60°C in l N H2so4 (pH = 0. 3). (a,

100 rnv/sec sweep-rate; b, 80 rnv/sec; c, 60 rnv/sec;

d, 50 rnv/sec; e, 40 rnv/sec; f, 30 rnv/sec; g,

20 rnv/sec; h, 10 rnv/sec)

Figure 11. Linear relationships between peak current and

square root of sweep-rate for 0.003 M fumaric acid

at 60°C in 1 N H2so4 (pH= 0.3). (O, Hg cathode;

f:'j., Hg/l%Bi; 0 1 Bi)

Figure 12. Linear relationships between peak current and

25

CAPTIONS FOR FIGURES (Can't)

fumaric acid concentration from 50 mv/sec

cathodic sweep at 60°C in 1 N H2so4 (pH= 0.3).

( Q, Hg cathode J L)., Hg/l%Bi; 0, Bi)

Figure 13. Variation of peak potential with sweep-rate for

0.003 M fumaric acid at 60°C in 1 N H2so4 (pH=

0.3). ( 0 1 Hg cathode; 6 1 Hg/l%Bi; O, Bi)

Figure 14. Variation of peak current with (Vp - E0 ) for

0.003 M fumaric acid at 60°C in 1 N H2so4 (pH =

0.3). ( Q, Hg cathode;-6., Hg/l%Bi; 0 1 Bi)

Figure 15. Current-potential curves from 50 V/sec cathodic

sweep on Hg at 60°C in 1 N H2so4 (pH= 0.3).

(curve A, 0.0003 M fumaric acid, curve B, no

fumaric acid) ..

Figure 16. Dependence of surface charges on sweep-rate

for 0.0003 M fumaric acid at 60°C in 1 N H2so4

(pH = 0. 3) • ( Q, Hg cathode;~' Hg/l%Bi; 0, Bi)

Figure 17. Fractional coverage-potential relationships for

fumaric acid from 50 V/sec cathodic sweep on Hg

at 60°C in 1 N H2so4 (pH = 0. 3). ( Q, 0. 0005 M

fumaric acid;~ 1 0. 0003 M; 0, 0. 0001 M)

CAPTIONS FOR FIGURES (Con't)

Figure 18. Fractional coverage-potential relationships


on Hg/l%Bi at 60°C in 1 N H2so4 (pH= 0.3).

( 0, 0.0005 M fumaric acid;~, 0.0003 M; Q,

0.0001 M)

26

Figure 19. Fractional coverage-potential relationships for

fumaric acid from 200 V/sec cathodic sweep on

Bi at 60°C in 1 N H2so4 (pH= 0.3). ( Q, 0.0005 M

fumaric acid;~, 0. 0003 ,M; 0, .(). 0001 lot)

27

-0.2

-w V5 -0.4 -0

> -0.6 "' >

-0.8

-6 -5 -4 -3

log i , amp- cm-2

Figure 1.

28

~

L1J :J: V) -In -0.4 .... 0 >

... > -0.6

-5 -4 -3

log I. amp.cm- 2 1

Figure 2.

29

.......... -0.2 w :r CJ) ~

(/) ...... -0.4 0 >

... >

-0.6

-4 -3 -2

log ·~ amp· cm-2 ,

Figure 3.

30

- -0.2 LLJ :J: (/) -(/) -0.4 ~

0 >

--> -0.6

-5 -4

log , amp. cm2

Figure 4.

-w ::c en -en ~

0 >

... >

-0.2

-0.4

-0.6

-0.8

-6 -5

log i ,

-4 -3

-2 amp·cm

Figure 5.

31

32

-0.2 -w ::1: (/) -en -0.4 .... 0 >

,..

> -0.6

-4 -3

log . I '

amp· crii 2

Figure 6.

C\J •E

0

0.. -4 E c

.. C)')

0

-5

-6

I og C ,

-2 -I

gmole ·I iter

Figure 7.

33

N •e

0 .

-3

-4

Q. E -5 0

,, .. -6

0' 0

-7

-6 -5 -4 -3 -2

-1 2 (gmole ·liter )

Figure 8.

34

-4

C\J 'E

(..) . ~

E 0

- -5 0' 0

--o-....

~

2.9 3.0

( T )-1 3 X I 0 ,

Figure 9.

--o-

0 -1 K

35

-o-

"""'6-

3. I

36

1.5 N

'E (.) . ~

E 0

I .0

-rt'>

0

X

0.5

-0.4 -0.5 -0.6

V , volts (SHE)

Figure 10.

37

6

C\J 5 'E

0 . 0.. 4 E 0

... 3 r<>o X 0.. 2

0. I 0.2 0.3 0.4

I I

u2 , (volts· sec-1>2

Figure 11.

38

N 10 IE 0

0.. E 0

rt') .. 0

X a.

0.00 I 0.0 I

C , gmo I e · I i t e r I

Figure 12.

-w :t: en -(/) ..... 0 >

0. >

39

-0.62

-0.64

0.0 I 0.1

u, volts· sec- I

Figure 13.

-w :::c en -(/) +-

0 :>

... -0 w I

>a. -

-0.9

- 1.0

- I . I

-2 amp em

Figure 14.

40

41

N IE 3 0 .

0.. E c

2 rt') ...

0

X

0 --0.2 -0.4 -0.6 -0.8 -1.0

V , volts (SHE)

Figure 15.

C\J •e

0 u :t. - I 0

Q) 0' ... 0 .s::. 0

Q)

g 5 '+... ~ (/)

42

100

v, volts· sec- I

Figure 16.

43

Q) 0 c ~ Q) > 0 (..) 0.1 c c: 0 +-(..) 0 ~

'+-

... CD

0 -O.I -0.3 -0.5

V, volts (SHE)

Figure 17.

44

0.2

Q) ~ c "-Q) > 0 0

- 0.1 0

8 .... 0 0 .....

'+-

ft

CD

q_O.I -0.3 -0.5

V, volts (SHE)

Figure 18.

45

Q) 0 0 "-Q)

~ 0

c; 0.1 c 0 ·-..... 0 0 "-......

... Q)

0 0 -0.2 -0.4

V, volts (SHE)

Figure 19.

APPENDIX A

MATERIALS

46

The following is a list of the major materials and

reagents used in this investigation. Detailed specifica

tions or analyses of the reagents may be obtained from the

catalogues of the suppliers.

1. Mercury. Triple distilled, instrument grade.

Bethlehem Apparatus Co., Inc., Hellertown, Pa.

2. Bismuth. 6N grade (99.9999% pure}. Electronic

Space Products, Inc., Los Angeles, Calif.

3. Fumaric Acid. Purified. Fisher Scientific

Company, Fairlawn, N.J.

4. Sulfuric Acid. Fisher Certified, A.C.S. Fisher

Scientific Company, Fairlawn, N.J.

5. Potassium Sulfate. Fisher Certified, A.C.S.

Fisher Scientific Company, Fairlawn, N.J.

6. Potassium Hydroxide. Fisher Certified, A.C.S.

Fisher Scientific Company, Fairlawn, N.J.

7. Nitrogen. Prepurified grade (99.997% pure}.

Matheson Gas Products, J)liet, Ill.

APPENDIX B

APPARATUS

47

1. Function Generator. Model CHF-1, Elron Electronic

Industries, Ltd., Haifa, Israel.

2. Potentiostat.

a. Model CHP-1, Elron Electronic Industries,

Ltd., Haifa, Israel.

b. Anotrol 4100, Continentia! Oil Co., Ponca

City, Okla.

3. Oscilloscope. Type 564B Storage Oscilloscope,

Tektronix, Inc., Portland, Oregon.

4. Electrometer. Model 610B, Keithley Instruments,

Inc., Cleveland, Ohio.

5. Power Supply. Model 711A, Hewlett-Packard Co.,

Loveland, Col.

6. Milliammeter. Model 931, Weston Instrument

Division, Daystron, Inc., Newark, N.J.

7. X-Y Recorder. Model 135AM, Hewlett-Packard Co.,

Pasadena, California.

APPENDIX C

SAMPLE CALCULATIONS FOR FUMARIC ACID DISSOCIATION

48

The dissociation of fumaric acid was determined from

the following three equations:

(H+) (HF-) (H2F) = Kl = 9.3 X 10-4 (1) *

(H+) (F=) = K2 = 3.4 X 10-5

(HF') (2) *

( 3)

where,

c0 = total concentration of fumaric acid.

From Eqs. (1), (2), and (3),

For example, at pH + = 0. 3, (H ) = 0.5,

(HF-)/C0 = 0.002

* d K f 25°C No data for 60°C were available. K1 an 2 are or •

TABLE VI

DEGREE OF DISSOCIATION OF FUMARIC ACID*

pH CH FICO CHF-/Co CF=/Co 2

0.3 0.998 0.002 0.000

1.5 0.972 0.028 0.000

2.2 0.865 0.134 0.001

2.9 0.576 0.420 0.011

3.7 0.155 0.722 0.122

*Sample calculations are shown in Appendix C

CH F = concentration of undissociated fumaric acid. 2

49

CHF- = concentration of singly-dissociated fumaric acid.

CF= = concentration of doubly-dissociated fumaric acid.

c0 = total concentration of fumaric acid.

APPENDIX D

EXPERIMENTAL DATA

50

51

TABLE VII

CURRENT-POTENTIAL RELATIONSHIPS FOR THE CATHODIC

REDUCTION OF FUMARIC ACID ON Hg* AT 60°C IN 1 N H2so4 (pH = 0. 3)

Fumaric acid concentration

0.03 M 0.003 M 0.0003 M

Potential Current Potential Current Potential Current

v, SHE rna V,SHE ma V,SHE rna

0.589** 0.591** 0.579** -0.13 0.006 -0.13 0.007 -0.13 0.006 -0.23 0.008 -0.23 0.007 -0.23 0.006 -0.28 0.011 -0.33 0.008 -0.33 0.0065 -0.33 0.023 -0.38 0.014 -0.405 0.009

-0.355 0.043 -0.43 0.037 -0.455 0.013 -0.38 0.08 -0.455 0.056 -0.48 0.021 -0.405 0.16 -0.48 0.11 -0.505 0.036 -0.43 0.33 -0.505 0.23 -0.53 0.063 -0.455 0.62 -0.53 0.38 -0.555 0.11

-0.48 1.3 -0.58 1.0 -0.58 0.17 -0.505 2.6 -0.605 1.4 -o. 63 0.33 -0.53 4.8 -0.63 2.0 -o .68 0.51 -0.58 13 -0.68 3.2 -0.73 0.85 -0.63 23 -0.73 3.4 -0.78 1.15

-0.68 32 -0.78 3.4 -0.83 1.9 -0.78 42 -0.83 4.5 -0.88 4.1 -0.83 43 -0.88 53

* Area = 10 2 em

** Rest potential

52

TABLE VII. (Continued)

Fumaric acid concentration

0.01 M 0.001 M

Potential Current Potential Current

V,SHE rna V,SHE rna

0.582** 0.579**

-0.13 0.006 -0.13 0.005

-0.23 0.006 -0.23 0.005

-0.33 0.01 -0.33 0.0065

-0.38 0.019 -0.38 0.01

-0.405 0.033 -0.43 0.023

-0.43 0.06 -o. 455 0.044

-0.455 0.135 -0.48 0.073

-0.48 0.27 -0.505 0.15

-0.505 0.58 -0.53 0. 2 8

-0.53 1.05 -0.555 0.48

-0.555 2.1 -0.58 0.77

-0.58 3.6 -0.63 1.2

-0.63 8 -o. 68 1.6

-0.7 14 -0.73 1.8

-0.75 14 -o. 78 2

-0.81 17

-0.88 23

** Rest potential

TABLE VIII


REDUCTION OF FUMARIC ACID ON Hg/l%Bi* AT

60°C IN 1 N H2so4 (pH = 0.3)

Fumaric Acid Concentration

0.03 M 0.003M 0.0003 M

53


V,SHE rna

0.205** -0.03 0.045 -0.18 0.046 -0.23 0.053 -0. 2"55 0.1

-0.28 0.16 -0.305 0.28 -0.33 0.53 -0.355 1.0 -0.38 1.9

-0.405 2.8 -0.43 4.9 -0.455 7.6 -0.48 11 -0.53 22

-0.58 30 -0.63 36 -0.73 42

* Area 10 2

= em

** Rest Potential

V,SHE

0.205** -0.13 -o. 2 3 -0.28 -0.33

-0.355 -0.38 -0.405 -0.43 -0.455

-0.48 -o. 53 -0.58 -0.63 -0.73

rna

0.056 0.06 0.075 0.135

0.21 0.33 0.53 0.78 1.15

1.6 2.55 3.3 3.6 4 .• 5

V,SHE rna

0.197** -0.13 0.042 .-0.23 0.042 -0.33 0.05 --o. 38 0.058

-0.405 0.09 -0.43 0.12 -0.455 0.16 -0.48 0.3 -o. 53 0.38

-0.58 0.51

TABLE IX


REDUCTION OF FUMARIC ACID ON Bi* AT 60°C

IN 1 N H2so4 (pH = 0.3)


0.03 M 0.01 M 0.003 M


V,SHE

0.215**

-0.03

-0.13

~o.l9

-0.21

-0.23

-0.255

-0.28

-0.305

-0.33

-0.36

-0.43

-0.48

-0.53

rna

0.12

0.12

o. 22

o. 26

0.5

0.95

2.2

4.9

9

15

21

23

23

-0.63 38

2 * Area = 3 em

** Rest Potential

V,SHE

0.225**

-0.03

-0.155

-0.205

-0.23

-0.255

-0.28

-0.305

-0.33

-0.355

-0.38

-0.43

-0.48

-0.58

rna

0.12

Q.l2

0\17

0.29

0.49

0.9

1.7

3.3

5

7

10

10

12

V ,SHE

0.23**

-0.03

-0.13

-0.205

-0.23

-0.255

-0.28

-0.305

-0.33

-0.355

-0.38

-0.405

-0.43

-0.53

rna

0.12

0.12

0.13

0.19

0.3

0.5

0.8

1.3

1.8

2.1

2.2

2.4

3.5

54

pH

TABLE X


REDUCTION OF 0.03 M FUMARIC ACID ON Hg* AT

60°C

= 1.5 pH = 2.2 pH = 2.9 pH

55

= 3.7

Pot. Current Pot. Current Pot. Current Pot. Current

V,SHE rna V,SHE rna V,SHE rna V,SHE rna

0.58** 0.585** - 0.58** 0.598** --0.13 0.003 -0.13 0.006 -0.23 0.004 -0.43 0. 014 -0.23 0.004 -0.23 0.007 -0.33 0.0045 -0.53 0.022 -0.33 0.007 -0.405 0.008 -0.43 0.007 -0.58 0.033 -0.38 0.016 -0.43 0.013 -0.48 0.011 -0.605 0.055

-0.43 0.03 -0.455 0.018 -0.53 0.028 -0.63 0.1 -0.455 0.055 -0.48 0.034 ~o.555 0.066 -0.655 0.25 -0.48 0.16 -0.505 0.05 -0.58 0 .• 19 -0.68 0.46 -0.505 0.34 -0.53 0.11 -0.605 0.42 -0.705 1 -0.53 0.72 -0.555 o. 21 -0.63 0.8 -0.755 1.8

-0.555 1.4 -0.58 0.48 -0.655 1.55 -0.805 2.9 -0.58 3.2 -0.605 1 -0.68 2.9 -0.88 10 -0.605 5.5 -0.63 1.7 -0.73 8.2 -0.63 10 -0.655 3.3 -0.78 15

-0.68 22 -0.705 11 -0.83 20 -0.78 40 -0.755 23 -o. 88 25 -0.83 45 -0.83 39

* Area = 10 2 ern

** Rest Potential

TABLE XI


REDUCTION OF 0.03 M FUMARIC ACID ON Hg/l%Bi*

AT 60°C

pH = 1.5 pH = 2.9


V,SHE rna V,SHE rna

0.2** 0.2**

0.03 0.02 -0.23 0.04

-0.17 0.022 -0.33 0.05

-0.28 0.06 -0.405 0.1

-0.305 0.095 -0.43 0.2

-0.355 0.2 -0.455 0.35

-0.38 0.35 -0.48 0.5

-0.405 0.62 -o. 505 0.91

-0.43 1.1 -0.53 1.6

-·o. 455 1.9 -0.555 2.6

-0.48 3.1 -0.58 3.4

-0.505 7.7 -0.605 5.5

-0.555 13 -0.655 11

-0.58 17 -0.73 23

-0.63 23 -0.83 30

-0.73 33

* Area = 10 crn2

** Rest Potential

56

57

TABLE XII

CURRENT-POTENTIAL RELATIONSHIPS FOR THE CATHODIC REDUC

TION OF 0.03 M FUMARIC ACID ON Bi* AT 60°C

pH = 1.5 pH = 2.9


V,SHE rna V,SHE rna

0.19** 0.16**

-0.03 0.15 -0.03 0.06

-0.13 0.15 -0.13 0.06

-0.23 0.15 -0.23 0.06

-0.28 0.21 -0.28 0.06

-0.305 0.305 -0.33 0.065

-0.33 0.54 -0.38 0.095

-0.355 0.8 -0.405 0.14

-0.38 1.55 -0.43 0.24

-0.405 3 -0.455 0.4

-0.43 4.8 -0.48 0.75

-0.455 8 -0.505 1.35

-0.48 9.5 -0.53 2.1

-0.53 15 -0.555 3.5

-0.63 21 -0.58 5.4

-0.63 10

-0.68 14

* Area = 3 crn2

** Rest Potential

TABLE XIII

CURRENT-POTENTIAL RELATIONSHIPS FOR HYDROGEN EVOLUTION

ON Hg AND Bi* AT 60°C IN 1 N H2so4 (pH= 0.3)

Hg

Potential Current

V,SHE rna

0.594** -0.13 0.006 -0.23 0.006 -0.33 0.009 -0.355 0.01

-0.405 0.011 -0.43 0.013 -0.455 0.015 -0.48 0.019 -0.505 0.025

-0.53 0.03 -0.555 0.045 -0.58 0.06 -0.605 0.09 -0.63 0.1

-0.68 0.21 -0.73 0.38 -0.78 0.7 -0.83 1.9 -0.88 4

Bi

Potential

V ,SHE

0.215** -0.03 -0.13 -0.205 -0.28

-0.33 -0.38 -0.43 -0.48 -0.53

-0.58 -0.63 -0.68 -0.73 -o. 78

Current

rna

0.11 0.11 0.115 0.115

0.12 0.13 0.165 0.25 0.46

1.3 3.2 7

28 60

* Area = 10 cm2 for Hg and Hg/l%Bi, 3 cm2 for Bi

** Rest Potential

58

TABLE XIV

CURRENT-TEMPERATURE RELATIONSHIPS FOR THE CATHODIC

REDUCTION OF 0.03 M FUMARIC ACID ON Hg*IN

1 N H2so4 (pH = 0.3)

Potential Temperature Current

V,SHE oc rna

-0.355 75 0.037 70 0.033 65 0.026 60 0.024 55 0.021 50 0.018

-0.405 75 0.162 70 0.155 65 0.14 60 0.118 55 0.105 50 0.09

-0.475 75 1.3 70 1.2 65 1.05 60 0.96 55 0.89 50 0.75

* Area = 10 cm2

59

TABLE XV


REDUCTION OF 0.03 M FUMARIC ACID ON Hg/1%Bi*

IN 1 N H2so4 {pH = 0.3)


V,SHE oc rna

-0.305 70 0.28

65 0.25

60 0.2 55 0.15

50 0.12

-0.355 70 1.1

65 0.89

60 0.8

55 0.6

so 0.51

-0.405 70 4.2

65 3.4

60 3.1

55 2.8

so 2.3

* Area = 10 cm2

60

TABLE XVI


REDUCTION OF 0.03 M FUMARIC ACID ON Bi* IN

1 N H2so4 (pH = 0.3)


V,SHE oc ma

-0.255 70 0.495

65 0.455

60 0.39

55 o. 345

50 0.29

-0.305 70 1.7

65 1.55

60 1.4

55 1.3

50 1.2

-0.355 70 6.5

65 5.75

60 5.5

55 5.15

50 4.8

* Area = 3 cm2

61

TABLE XVII

PEAK CURRENT-PEAK POTENTIAL RELATIONSHIPS FROM CATHODIC

SWEEPS FOR FUMARIC ACID ON Hg* AT 60°C IN 1 N H2so4 {pH = 0. 3)


Sweep 0.001 M 0.003 M Rate

Peak Peak Peak Peak Potential Current Potential Current

mV/sec V,SHE rna V,SHE rna

10 -0.515 2.35 -0.52 6.5 20 -0.528 3.0 -0.537 8.38 30 -0.535 3.55 -0.543 10.13 40 -0.54 4.0 -0.552 11.73 50 -0.549 4.55 -0.56 12.75

60 -0.554 4.9 -0.564 13.75 80 -0.56 5.5 -0.571 15.75

100 -0.565 6.3 -0.578 17.3 150 -0.575 7.35 200 -0.58 8.38

0.01 M 0.03 M

10 -0.555 22.5 -0.555 63 20 -0.565 28.75 -0.575 81.5 30 -0.575 34 -0.59 94.5 40 -0.582 38.75 -0.602 107 50 -0.592 43 -0.608 120

60 -0.60 47 -0.616 128 ,so -0.606 53.75 -0.622 146 100 -0.617 58 -0.637 160 150 -0.63 70 200 -0.642 81.5

* 10 2 Area = em

62

*

63

TABLE XVIII


SWEEPS FOR FUMARIC ACID ON Hg/l%Bi* AT 60°C IN

1 N H2so 4 (pH= 0.3)


Sweep 0.003 M 0.01 M Rate


V/sec V/SHE rna V/SHE rna

20 -0.589 6.6 -0.613 27

30 -0.599 8.1 -0.625 32

40 -0.605 9.4 -0.633 36

50 -0.612 10.5 -0.64 39

60 -0.618 11.6 -0.648 42.5

80 -0.624 13.3 -0.657 48.5

100 -0.631 14.6 -o. 6-61 53

150 -0.644 17.6 -0.673 63

200 -0.649 20 -0.683 72

10 2 Area = em

64

TABLE XIX


SWEEPS FOR FUMARIC ACID ON Bi* AT 60°C IN 1 N H2so4 (pH = 0. 3)

Sweep Rate

rnV/sec

20

30

40

50

60

80

100

150

200

0.003

Peak Potential

V,SHE

-0.37

-0.38

-0.388

-0.395

-0.4

-0.415

-0.42

-0.43

-0.442

* Area = 3 crn2

M

Peak· Current

rna

6.3

7. 6

8.7

9.6

10.4

11.8

13

15.6

17


0.01 M 0.03 M


V,SHE rna V,SHE rna

-0. 39 3 17 -0.422 64

-0.405 20.5 -0.456 77

-0.412 23 -0.47 87

-0.418 26.5 -0.48 97

-0.425 29 -0.49 104

-0.43 33 -0.505 119

-0.438 37 -0.51 130

-0.452 44 -0.523 154

-0.462 ' 50.5 -0.545 172

Sweep Rate

V/sec

15

20

30

40

50

70

100

150

TABLE XX

SURFACE CHARGE-SWEEP RATE RELATIONSHIPS FROM

CATHODIC SWEEPS FOR 0.0003 M FUMARIC ACID

AT 60°C IN 1 N H2so4 (pH = 0.3)

Hg*

Surface Charge

].lC

13.5

11.7

9.3

7.6

6.9

6.4

5.1

3.5

Sweep Rate

V/sec

20

30

40

50

70

100

150

Hg/1%Bi*

Surface Charge

].lC

10

8.13

6.68

5.6

5.55

4.35

3.7

Sweep Rate

V/sec

70

100

150

200

250

300

400

500

Bi**

Surface Charge

].lC

13.5

10.2

7.92

6.67

6.25

5.4

4.4

2.1

* Area = 0. 4 2 em

** Area 2 = 0.48 em

65

TABLE XXI

SURFACE-CHARGE-POTENTIAL RELATIONSHIPS FROM 50 V/SEC

CATHODIC SWEEPS ON Hg* AT 60°C IN 1 N H2so4 (pH = 0. 3)


Potential 0.0001 M 0.0003 M 0.0005

Surface Surface Surface Charge Charge Charge

V,SHE lJC/cm 2 lJC/cm2 lJC/cm 2

-0.13 2.2 6.8 10.77

-0.23 2.2 6.8 10.77

-0.33 2.1 6.5 9.94

-0.38 1.25 5.0 8.67

-0.43 0.6 2.0 5.67

-0.48 1.5

-0.53 0.06 0.3 0.68

* Area = 0.4 2 em

66

M

TABLE XXII

SURFACE CHARGE-POTENTIAL RELATIONSHIPS FROM 50 V/SEC

CATHODIC SWEEPS ON Hg/l%Bi* AT 60°C IN 1 N H2so4 {pH = 0. 3)

Potential

V,SHE

-0.13

-0.23

-0.33

-0.38

-0.43

-0.48

-0.53

* Area= 0.4

0.0001

Surface Cha~ge

].lc/crn 2

2.3

2.3

2.3

1.39

0.78

0.18

2 ern


M 0.0003 M 0.0005 M

Surface Surface Charge Charge

J.lC/ ern 2 ].lc/crn2

7.5 12.6

7.5 12.6

6.7 11.27

3.84 6.6

1.47 2.06

0.75

0.56 0.57

67

TABLE XXIII

SURFACE CHARGE-POTENTIAL RELATIONSHIPS FROM 200 V/SEC

CATHODIC SWEEPS ON Bi~ AT.60°C IN.lNHz;o,4 . (pH = 0. 3)


Potential 0.0001 M 0.0003 M 0.0005

Surface Surface Surface Charge Charge Charge

V ,SHE ]Jc/cm 2 ]Jc/cm 2 J.1C/cm2

-0.03 2.3 6.65 12.5

-0.13 2.3 6.65 12.0

-0.23 1.7 5.6 10.0

-0.28 1.0 4.1 4.7

-0.33 0.8 1.5 2.3

-0.38 1.0

-0.43 0.1 0.4 0.6

*Area 0.48 2 = em

68

M

69

APPENDIX E

A MICRO-DETERMINATION OF SUCCINIC ACID

1. Extraction. A portion of the electrolyte containing

about 40 mg of succinic acid was acidified with cone.

sulfuric acid to Congo Red. It was heated on a water

bath and treated with 0.1 N KMn0 4 until a brown pre

cipitate was obtained. The precipitate dissolved by

addition of Na2so3 and the solution evaporated to

10 ml. The whole residue was transferred quantita

tively to an extractor* and saturated with K2so4 •

After extracting 24 hours with ether, the later; was

transferred to a flask and 30 ml of distilled water

added. The ether was removed by heating.

2. Titration. The pH of the solution was adjusted to

6.5 - 7.0 with 0.05 N KOH and a measured excess of

0.1 N AgNo3 added immediately. The resulting pre

cipitate was kept for 2 hours in the dark. The

solution was filtered through a fritted glass filter

and washed quantitatively from the flask on to the

filter by three successive portions of 1% NH 4No3

(3 ml, 3 ml, and 2 ml). To this was added 30 ml of

1 N HN03 and about 7-9 drops of 10% Fe(N03 ) 3 as an

indicator to the filtrate and then titrated with

0.1 N NH4SCN until a faint brown color appeared.

*No. 92225, corning catalog "Pyrex Laboratory Glassware", Corning Glass Works, Borning, N.Y.

3. Sample Calculation. The method of calculating the

efficiencies was the same for all solutions. The

70

data from Table XXIV have been used in the following

illustration.

The theoretical amount of succinic acid was

calculated using Faraday's Law:

= ItA/nF

= (1.5xl0- 3 ) (65.5) (3600) (118) (1000) (2) (96500)

= 216 mg

The experimental amount of succinic acid was

determined using a 50 ml sample (total 300 ml) which

had been electrolyzed for 65.5 hours with a current of

1.5 rna. The excess AgNo3 amounted to 9.2 ml of

NH4scN to precipitate the silver succinate was 5.8 ml.

Since one ml of 0.1 N AgN03 is equivalent. to 5.9 mg of

succinic acid, the amount of succinic acid in the 50 ml

sample was 34.22 mg and the total succinic acid in the

300 ml solution was 205.32 mg.

Therefore,

Eff = 205.32/216 = 95%

TABLE XXIV

DATA FOR THE COULOMBIC EFFICIENCY STUDIES OF THE

CATHODIC REDUCTION OF FUMARIC ACID TO SUCCINIC

ACID

Electrode

Hg

II

Hg/1% Bi

II

Bi

II

pH v v

ml ml

0.3 300 50

2.9 250 100

0.3 250 60

2.9 250 50

0.3 300 60

2.9 400 30

AgN03 added

0.1

15

15

15

15

15

15

N

V = Total volume of electrolyte

NH 4SCN

used

0.1 N

9.2

7.8

6.1

8.8

5.0

10.2

Succinic acid

mg

205

106

219

183

295

377

v = Volume of electrolyte used for analysis

71

72

VITA

Chen Hwei Chi was born on October 3, 1941 in Kiang-su,

China. He graduated from high school in 1959. He entered

Chung Yuan College of Science and Engineering and graduated

with a B.S. degree in Chemical Engineering in June, 1963.

After graduation, he served in the Chinese Army for a

period of one year and was assigned as a second lieutenant.

He came to the United States and enrolled in the

Graduate School of the University of Missouri-Rolla in

September 1967. He received the Master of Science degree

in Chemical Engineering in May 1969. He continued work

toward the degree of Doctor of Philosophy in Chemical

Engineering. He received a research scholarship from 1968

to 1971 from the Graduate Center for Materials Research.

the electrochemical reduction of fumaric acid on hg-bi

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