Mo-Fe cathode

8/7/2019 Mo-Fe cathode

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Electrochimica Acta 50 (2005) 55945601

Kinetics of the hydrogen evolution reaction on FeMo filmdeposited on mild steel support in alkaline solution

N.R. Elezovic a, V.D. Jovic a, N.V. Krstajic b,

a Center for Multidisciplinary Studies, University of Belgrade, 11030 Belgrade, Serbia and Montenegrob Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia and Montenegro

Received 12 November 2004; received in revised form 21 January 2005; accepted 5 March 2005

Available online 17 May 2005

Abstract

The mechanism and kinetics of the hydrogen evolution reaction were studied in 1.0 mol dm3 NaOH solution on FeMo alloy elec-

trodes prepared by electrodeposition at constant current densities from a pyrophosphate bath. A series of electrode containing 3459 at.%

Mo was prepared. Electrodes displayed porous character, and electrochemical impedance spectroscopy was used to characterized real

surface area. It was found that within the whole potential region the mechanism of the HER is a consecutive combination of the

Volmer step, followed dominantly by a rate controlling Heyrovsky step, while the contribution of the parallel Tafel step is negligible.

The kinetic parameters of the HER were determined. With an increase in the molybdenum content, the electrodes become more ac-

tive, and an increase in the real surface area is observed. The main factor influencing the electrode activity seems to be the real surface

area.

2005 Elsevier Ltd. All rights reserved.

Keywords: Hydrogen evolution; FeMo electrodes; Alkaline solution; Impedance; Mechanism

1. Introduction

The hydrogen evolution reaction (HER) is of technologi-

cal importance for such processes as water electrolysis, chlo-

rate and chlorine production. For these applications materials

with low overpotential are needed.

Miles [1] suggested that a combination of two metals from

the two brunches of volcano curve could result in enhanced

catalytic activity. Jaksic [2] showed that a combination of Ni

or Co with Mo could result in a substantial enhancement of

the HER.Numerous studies thoroughlyinvestigated the kinetics and

mechanism of the HER at NiMo [312] alloys of various

compositions, obtained by suitable baths. All these electrodes

are characterized by having a high roughness factor.

However, despite extensive studies, in the case of chlorate

cell process, mild steel is a traditional cathode material and its

Corresponding author.

E-mail address: [email protected] (N.V. Krstajic).

substitution by more active catalysts based on combination

of Co or Ni with Mo up to now is not successful. The main

reason is probably the fact that Co or Ni ions present in the

solution at very low concentration as corrosion product cat-

alytically degrade active chlorine (ClO, HClO) which lead

to substantial current losses [13].

In this study, we report the results regarding the HER on

some FeMo coatings prepared by the electrochemical de-

position from suitable pyrophosphate bath [14] on mild steel

substrate. The main purpose is to study the mechanism and

kinetics in order to determine surface coverage by adsorbedhydrogen and to understand the source of the electrode ac-

tivity.

2. Theory

Generally, the mechanism of the HER in aqueous acid

solutions is treated as a combination of three basic steps, two

electrochemical and one chemical:

0013-4686/$ see front matter 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.electacta.2005.03.037


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N.R. Elezovic et al. / Electrochimica Acta 50 (2005) 55945601 5595

H3O+ +M+ e

k1k1

MHads +H2O (1)

followed by

MHads +H3O+ + e

k2k2

M+H2 +H2O (2)

and/or

2MHadsk3k3

2M+H2 (3)

The rates of corresponding steps are given by

v1 = k1(1 H)exp

1F

RT

k1H

exp

(1 1)

F

RT

= k1(1 H) k

1H (4a)

v2 = k2H exp

2F

RT k2(1H)

exp

(1 2)

F

RT

= k2H k

2(1H) (4b)

v3 = k32H k3(1 H)

2 (4c)

In these rate laws surface concentrations of the interme-

diate Hads and the corresponding free adsorption sites at

the electrode are given as the coverage (H), or surface

sites concentrations (1H). The chemical rate constants

ki (mol cm2 s1) have nominally been written to include

H3O+

ion concentration, in the 0.5mol dm3

HClO4 solu-tion.

Under open circuit conditions all three reaction steps are

in equilibrium with net reaction rates equal to zero so that

v1 = v2 = v3 = 0 (5)

In this case and according to Eq. (5) only four out of six rate

constants are independent parameters, i.e. k1, k2, k1, and k3,

while k2 = (k1k2)/k1, and k3 = k21k3/k

21.

The steady-state kinetics of the HER at constant current

density are characterized by the conditions of the charge bal-

ance (with rates in mol cm2 s1):

r0 =jF= (v1 + v2) (6)

and the mass balance with respect to the intermediate Hads:

r1 =q1

F

dH

dt= v1 v2 2v3 (7)

q1 is the charge necessary for a monolayer coverage by ad-

sorbed hydrogen.

When a particular value of the mass balance, i.e. r1 = 0

is set, the steady-state coverage can be calculated, assuming

that the Langmuir adsorption isotherm is operable. Calcu-

lations showed that the rate constants k2 and k3 of the

backward reactions of steps 2 and 3 could be neglected be-

cause they have no significant influence on the reaction rates

of the second (Eq. (4b)) and third step (Eq. (4c)) at overpo-

tential 60 mV, and the steady state coverage (H), of

the intermediate Hads species is the following function of the

corresponding rate constants:

H = (k1 + k

1 + k

2) +

(k1 + k

1+k

2)

2+ 8k1k3

4k3(8)

and the pseudocapacitance, C is given by

C =q1dH

d(9)

The presence of the electrochemical rate constants in Eq. (8)

clearly indicates the rather complex dependence ofH on

the electrode potential.

Theoretically, six variables, i.e. four independent chemi-

cal rate constants of the three basic steps and two symmetry

factors of the electrochemical steps (1 and 2) can describe

the mechanism of the HER on the electrode in the corre-

sponding solution. However, it can be reasonably assumed

for elementary electrode reactions, that 1 =2 = 0.5. With

this assumption the problem is reduced to the determination

of four independent variables, i.e. k1, k1, k2, k3.

The Faradaic impedance of the HER is described by the

following equation [15]:

1

Zf=

1Rct

+1

1Rp+ jCp

1

(10)

The equation is written directly from Armstrongs equivalent

circuit [16].

The equivalent circuit elements: Rct, Rp, Cp are complex

functions of the kinetic parameters and are given [17] by

R1ct = F

v1

E

H

+

v2

E

H

=

F2

RT

[k1(1 H) k

1H + k

2H] (11a)

Generally, it is reasonable to assume that more than one

of the basic steps is involved in the mechanism of the HER,which means that the value of the experimental Tafel slope

is determined by the reciprocal of the Faradaic resistance

(i.e. the sum of charge transfer and pseudo resistances)

(Rct + Rp)1, where the pseudo resistance is presented by

Rp = R20

Rct +R0(11b)

and the parameter R0 is defined as follows:

R10 =F2p

q1

v1

H

E

+

v2

H

E

(11c)


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5596 N.R. Elezovic et al. / Electrochimica Acta 50 (2005) 55945601

Fig. 1. CPE equivalent circuit used for the HER.

with the time constant p equal to

1p =F

q1

2

v3

H

E

+

v2

H

E

v1

H

E

(11d)

However, on solid electrodes, the double-layer capaci-

tance is substituted by a constant phase element (CPE) its

impedance is given as [18]:

ZCPE =1

T(j)(12)

where Tis capacitance parameter (in Fcm2 s1) and 1

is a parameter characterizing rotation of the complex plane

impedance plot. The double-layer capacitance may be esti-

mated from [18]:

T= Cdl(R1 +R

1ct )

1(13)

This is the so-called CPE model and it is presented in

Fig. 1. It predicts the formation of two depressed semicircles

on the complexplane plots.

3. Experimental

3.1. Cell and chemicals

A conventional three-compartment cell was used. The

working electrode (WE) compartment was separated by frit-

ted glass discs from the other two compartments. The WE

compartment was jacketed and thermostated during measure-

ments at 25.0 C using an ultrathermostat. All measurements

were performed in 1.0 mol dm3 solution of NaOH (Spec-

trograde, Merck), prepared in deionized water.

The WE compartment was saturated with purified hydro-

gen at standard pressure during measurements.

3.2. Electrodes

Allsamples were depositedon mild steel substrates having

a surface area of 1 cm2. The steel substrates were first sand

blasted using 50m particles, degreased in NaOH-saturated

ethanol for 5 min, then etched in 25 wt.% HCl for 2 min. Af-

ter this procedure samples were washed with distilled water,

dried and weighted and then immersed in the solution for

FeMo alloy electrodeposition. FeMo film was deposited

on one side of the electrode. The inactive walls of the sup-

port were protected from the solution by the alkaline resistant

epoxy resin. After deposition samples were washed, driedand weighted again to determine the mass of the alloy. All

solutions were made using distilled-deionized water and an-

alytical grade chemicals.

FeMo alloys were deposited to a constant charge of

36Ccm2 at three different current densities: 100 mA cm2

(FeMo100), 50 mA cm2 (FeMo50) and 20 mA cm2

(FeMo20), from the plating bath with the following compo-

sition: 9 g dm3 of FeCl3, 40 g dm3 Na2MoO4, 75 g dm

3

NaHCO3 and 45gdm3 Na4P2O7 at 60

C. A Pt mesh,

placed parallel to the cathode, was used as a counter elec-

trode during electrodeposition and electrolyte was moder-

ately stirred with the magnetic stirrer.

The counter electrode was a platinum sheet of 5 cm2 geo-metric area.

The reference electrode was the Hg|HgO electrode in

1.0moldm3 NaOH, held at a constant temperature of 25 C.

All potentials are referred to the standard hydrogen electrode

scale (SHE). The calculated value of the equilibrium poten-

tialoftheHERin1.0moldm3 solution of NaOH (pH13.86)

at 25.0 C is 0.818 V.

3.3. Measurements

Tafel lines were recorded using potentiostatic steady-state

voltammetry, point by point at 60 s intervals, in the range ofpotential from 1.12 to 0.82 V, using a PAR 273 potentio-

stat, with good reproducibility of measurement.

Whenever the potential of the WE approached approxi-

mately 1.1 V (or when current densities were close to, or

above approximately 0.1 A cm2) it was found that the un-

compensated solution resistance was significant. Therefore,

the IR drop was systematically determined in all measure-

ments, using ac impedance methods. All data presented in

this article are corrected for the IR drop.

Simultaneously with the Tafel lines, electrochemical

impedance spectra of the WE at selected constant potentials

were determined, using a PAR 273 potentiostat, together with

a PAR 5301 lock-in-amplifier, controlled through a GPBI

PC2A interface. The fast Fourier transformation (FFT) tech-

nique was used in the impedance measurements in the fre-

quency region below 5 Hz. So, both impedance spectra in

the complex plane and corresponding Bode diagrams were

obtained in the frequency range from 50 mHz to 100 kHz,

at the constant potentials of the WE. In all measurements

above 5 Hz, ten frequency points per decade were taken. The

real and imaginary components of the impedance spectra in

the complex plane were analyzed using the nonlinear least

squares (NLSs) fitting program to determine the parameters

of the proposed equivalent circuit. The rate constants were


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calculated by minimizing the residual (S) of the sum of each

experimental datum (the dc polarization measurements and

ac impedance results).

The real electrode surface area was evaluated from in situ

measurements of double-layer capacitance, determined from

initial potentialdecay slopes (d/dt) following interruption

of significant, overpotential ()-dependent, Faradaic currentspassing across the electrode/electrolyte interface. Potential-

relaxation transients were recorded digitally by computer

over five to six decades of time using a very fast electronic

switcher.

Scanning electron microscopy (SEM-JOEL 840) was

used to characterize the as-deposited surfaces and en-

ergy dispersive X-ray spectroscopy (EDS) to determine

alloy composition. Selected deposits were mounted in

cross-section, polished and examined by optical microscopy.

4. Results and discussion

4.1. Composition and morphology of the FeMo alloys

The influence of the current density (potential) on current

efficiency and alloy composition is presented in Table 1. As

can be seen the content of Mo increases, while the content of

Fe decreases with increasing average current density.

In Fig. 2 are shown typical top view of FeMo alloy (a)

and a cross section of the deposit of a thickness of about

20m (b). As can be seen morphology of FeMo alloys is

characterized by the presence of micro-cracks, with some

of them being up to 2m wide (Fig. 2(b)). It is important

to note that the surface of the samples deposited at lower

Table 1

The influence of the current density for deposition of FeMo coatings, jdep,

on current efficiency, i, and alloy composition

Electrode jdep(mAcm2)

Mo (at.%) Fe (at.%) Current efficiency,

i (%)

FeMo20 20 34.0 66.0 36.8

FeMo50 50 41.8 58.2 32.0

FeMo100 100 59.3 40.7 29.8

Table 2

Kinetic parameters for the HER obtained from the polarization curves in

1.0moldm3 NaOH at 25 C

Electrode FeMo20 FeMo50 FeMo100

b1 (mV) 36 35 37

b2 (mV) 127 124 125

j0 (106 A cm2) 1.8 4.2 20.4

j (103 A cm2) (=0.2 V) 14.6 32.7 59.3

current densities (examined with the naked eye) seemed to

be less rough.

4.2. Polarization measurements

The polarization curves obtained on different FeMo

electrodes are shown in Fig. 3, and Table 2 presents

the kinetics parameters j0 and Tafel slopes, b, for those

electrodes. Polarization curves were recorded after holding

the electrodes at a constant cathodic current density of

100mAcm2 for about 1 h. The electrode containing

59.3 at.% molybdenum (FeMo100) is found to have the

lowest hydrogen overpotential, and the highest exchange

current density, j0 2 105

A cm2

. The polarization

Fig. 2. (a) Scanning electron micrographs of the FeMo electrode surface (1) FeMo100 (59.3% Mo); 2) FeMo50 (41.8% Mo); (3) FeMo20 (34% Mo).

Magnification 1000. (b) Cross-section of the FeMo100 deposit of a thickness of about 20m.


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Fig. 3. Tafel polarization curves for the HER on FeMo electrodes in

1.0moldm3 NaOH at 25 C.

curves are characterized by two Tafel slopes at all electrodes,

40 mV at lower overpotential region and 120 mV at

high overpotential region.

4.3. ac Impedance

Typical complex plane plots for an electrode containing

59.3 at.% Mo (FeMo100) are shown in Fig. 4 and Bode

plots in Fig. 5. Two overlapped semicircles was found for

all FeMo electrodes at all overpotentials. Data presented in

Figs. 4 and 5 are interpreted by NLS fitting procedure [19]

to determine the elements of the equivalent circuit, given in

Fig. 1. The values of all parameters obtained by this proce-

dure, which are necessary to calculate therate constantsin the

mechanism of the HER are presented in Table 3. The ohmic

resistance of the solution was R =0.69cm2.

4.4. Surface roughness

Using the NLS fit of the experimental impedance data to

the CPE model parameters characterizing the double-layer

may be obtained. From the parameters Tand it is possible

to determine an average double-layer capacitance. However,

the value of the parameter , which is close to 0.5 is too

Fig. 4. Impedance spectra in the complex plane for the HER on FeMo100

electrode at four constant overpotential within the Tafel region of the po-

larization curve. Circled points are experimental data and solid lines are

calculated using the NLS fitting procedure.

Fig. 5. Bode plot for the HER on FeMo electrodes in 1.0mol dm3 NaOH

at 25 C. Solid lines are calculated using the NLS fitting procedure using the

corresponding values for q1, assigned in figure.

low and Eq. (13) cannot be used to estimate the average Cdl.

For determination of double-layer capacity the open circuit

potential decay method was used. In this technique, poten-

tial decay is monitoring after the opening of the circuit. The

overpotentiallogarithm of time curve for FeMo100 elec-

trode is presentedin Fig.6. It is evident that theelectrode does

not relax to the equilibrium potential even after 10 seconds

indicating the presence of a large pseudocapacitance. Open

Table 3

Values of the approximated elements of the CPE equivalent circuit for the HER at FeMo100 in 1.0 moldm3 NaOH at 25.0 C, taken at the constant

overpotentials

(V) Rct ( cm2) Error (%) Rp ( cm

2) Error (%) Cp (Fcm2) Error (%) T(Fcm2 s1) Error (%) Error (%)

0.055 2.04 5.2 56.3 3.9 0.046 8.1 0.13 8.5 0.54 3.5

0.064 2.03 4.8 35.9 3.5 0.048 6.6 0.14 8.1 0.54 3.2

0.074 1.33 4.6 12.8 4.9 0.070 6.6 0.19 6.7 0.49 2.1

0.087 1.31 5.5 7.67 4.8 0.080 6.2 0.16 5.9 0.49 1.9

0.120 1.05 5.3 2.64 5.6 0.12 6.1 0.16 4.9 0.53 1.7

0.128 0.99 6.5 2.14 5.7 0.13 5.9 0.16 4.6 0.53 1.6

0.150 0.86 6.1 1.32 7.1 0.14 5.7 0.16 4.4 0.52 1.5

0.164 0.78 6.5 0.95 7.0 0.16 5.6 0.15 4.3 0.43 1.4


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Fig. 6. Overpotential, , against log time, tplot for the HER at FeMo100

electrode recordered after interruption of polarization at overpotential

=0.44 V in 1.0 mol dm3 NaOH at 25 C.

circuit potential decay can be can be presented by the follow-ing equation [20]:

C + Cdl =j

ddt

(14)

where C is an pseudocapacitance and j is the measured

steady-state current density at the overvoltage . In order to

analyze this equation the derivative d/dtmust be determined

from the experimental t curves. Corresponding d/dt

curves obtained after numerical differentiation is shown in

Fig.7. At more negative overpotentialregion, where the pseu-

docapacitance is negligible, the double-layer capacitance can

be determined. The corresponding C curves for FeMoelectrodes obtained using Eq. (14) are presented in Fig. 8.

The double-layer capacities Cdl, increase with an increase in

the molybdenum content (Table 4).

From the double-layer capacitances the real electrode sur-

face area andthe surface roughness(R)canbeestimated,ifthe

double-layer capacitance for a smooth surface is known. Tak-

ing into account the value of ca. 20 F cm2 used earlier in

the literature [21,22], the values of the surface roughness ob-

Table 4

Double-layer capacitance values, surface roughness, and intrinsic activities

for FeMo electrodes in 1.0 moldm3 NaOH at 25 C

Electrode Cdl (mFcm2) R j0R1 (108 A cm2)

FeMo20 2.5 125 1.4

FeMo50 7 350 1.2

FeMo100 11 550 3.7

Fig.7. against (d/dt) plots forthe HERat FeMo100electrode obtained

by the numerical differentiation of initial part oftcurve presented in this

figure.

Fig.8. The capacitance, C, against overpotential plots forthe HERat FeMo

electrodes in 1.0 moldm3 NaOH at 25 C.

tained are included in Table 4. They indicate that the surface

roughness increases with increase of molybdenum content in

the alloy.

However, one should keep in mind that if the high fre-

quency data produced a distorted semicircle in complex plane

impedance plot with the parameter 0.5, the short time po-

tential decay curves (presented in Fig. 8) are also affected by

this problem, because there is an equivalence between time

and frequency data, which means that it is not possible ac-

curately to determine the double-layer capacitance of these

electrodes even with the open circuit potential decay method.

Table 5

Values of the rate constants (in mol cm2 s1) for individual steps of the HER on FeMo electrodes in 1.0 mol dm3 NaOH at 25 C

Electrode k1 k1 k2 k2a k3 k3

a

FeMo20 (34 at.% Mo) 1.5108 1.0106 2.1109 3 1011 1108 2.31012

FeMo50 (41.8 at.% Mo) 3 108 2 106 3 109 4.5 1011 3108 6.81012

FeMo100 (59.2 a t.% Mo) 6 108 5 106 6 109 5 1011 6108 4.41012

a k2 = (k1k2)/k1; k3 = k21k3/k

21.


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Fig. 9. Experimental (circled points) and simulated of: (1) Tafel plot; (2)

vs. log[1/(Rct +Rp)]; (3) vs. log (1/Rp); (4) vs. log (1/Rct) for the HER

at FeMo100 in 1.0mol dm3 NaOH solution.

Fig. 10. Simulated curves, numerically calculated for the set of rate

constants for the HER at FeMo electrodes in 1.0 mol dm3 NaOH solution

at 25 C.

Fig. 11. Overpotential dependence of the theoretically calculated individual rates for the Volmer, Heyrovsky and Tafel steps occurring simultaneously with the

HER on FeMo electrodes in 1.0mol dm3 NaOH solution at 25 C. Theoretical polarization curve, obtained by summing individual curves is represented by

full lines. Experimental data are presented by circled points.


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4.5. Rate constants

The rates constants of the individual steps for the HER

was determined from polarization measurements and fitted

parameters values of CPEequivalent circuit using NLSfitting

procedure [19].

The estimated values of the rate constants are presentedin the Table 5, for the apparent surface area of 1 cm2.

The complexplane impedance diagrams calculated from

the evaluated k1 values are presented by the solid lines in

Figs. 4 and 5.

Conway and coworkers [17] have shown that at suffi-

ciently high when H is almost constant and for Lang-

muiran adsorption, the theoretical separation between j

and the simulated log(Rct +Rp)1 plots (curves 1 and 2

in Fig. 9) isequalto log (F/RT). With = 0.5 and T=298K,

log(F/RT) = 1.29, which is close to the observed separation

between the two lines of 1.31. This analysis proves the Lang-

muiran adsorption of H for the HER at FeMo electrodes.

Using the values of the rate constants from Table 5, andEq. (8) it is possible to calculate the dependence ofH on the

overpotential of the FeMo electrodes, which are presented

in Fig. 10. It is interesting to note, that this dependence is

almost the same for all FeMo electrode.

The calculated values of the maximum charge of the WE,

q1, obtained by fitting of Bode plots (Fig. 5) are close to

15mCcm2 for FeMo100, 5 mC cm2 for FeMo50 and

3mCcm2 for FeMo20 electrodes.

The reaction rates of the Volmer, Heyrovsky and Tafel

steps in the mechanism of the HER and the resulting total

current value areall independently shown in Fig. 11, as calcu-

latedfromthecorresponding ki values, in a wideoverpotentialregion. In this figure, all the rate values, vi (mol cm

2 s1)

are shown in terms of current density, Fvi (Acm2).

From Fig. 11, one can conclude that the reaction

mechanism is a consecutive combination of Volmer and

Heyrovsky step and that Heyrovsky step prevails over Tafel

step in low overpotential region at all investigated FeMo

electrodes. Reaction rate is controlled by the Heyrovsky

reaction because of the much smaller k2 value as compared

with the k1 and k3 values.

The intrinsic activity, that is the rate constant of the

limiting step per real surface area or the exchange current

density per real surface are, k2/R, or j0/R, was estimated

(see Table 4). Intrinsic activities of FeMo20 (34 at.% Mo)

and FeMo50 (41.8 at.% Mo) are similar and smaller than

FeMo100 (59.3 at.% Mo).

5. Conclusions

Polarization measurements and the ac impedance mea-

surements were used to determine the mechanism and the

kinetics of the electrodeposited FeMo alloy electrodes. The

surface roughness estimated using the double-layer capac-

itance ratio shows that real surface area increases with in-

crease in the molybdenum content. This factor is principally

responsible for the increased activity.

The rate constants of the forward and backward re-

actions of Volmer, Heyrovsky and Tafel steps were esti-mated by a non-linear fitting method of the experimen-

tal results obtained from polarization and impedance mea-

surements. The HER proceeds through VolmerHeyrovsky

mechanism and reaction rate is controlled by Heyrovsky

step.

Acknowledgement

This paper has been supported by the Ministry of Sci-

ence and Environmental Protection, Republic of Serbia, un-

der Contract No. 1825.

References

[1] M.H. Miles, J. Electroanal. Chem. 29 (1984) 1539.

[2] M.M. Jaksic, Electrochim. Acta 29 (1984) 1539.

[3] B.E. Conway, L. Bai, M.A. Sattar, J. Hydrogen Energy 12 (1987)

607.

[4] I.A. Raj, K.I. Vasu, J. Appl. Electrochem. 22 (1992) 471.

[5] B.E. Conway, L. Bay, D.F. Tessier, J. Electroanal. Chem. 161 (1984)

39.

[6] C. Fan, D.L. Piron, P. Paradis, Electrochim. Acta 39 (1994)

2715.

[7] B.E. Conway, L. Bai, J. Chem. Soc., Farady Trans. 81 (1985)

1841.[8] I.A. Raj, V.K. Venkatesan, Int. J. Hydrogen Energy 12 (1988)

215.

[9] C. Fan, D.L. Piron, A. Sleb, P. Paradis, J. Electrochem. Soc. 141

(1994) 382.

[10] J.D. Schmotz, J. Balej, J. Appl. Electrochem. 19 (1989) 519.

[11] B.E. Conway, L. Bay, M.A. Sattar, Int. J. Hydrogen Energy 12 (1987)

607.

[12] A. Lasia, A. Rami, J. Electroanal. Chem. 294 (1990) 123.

[13] H. Yoshida, T. Akazawa, T. Haneda, Denki Kagaku 41 (1973)

68.

[14] L.O. Case, A. Krohn, J. Electrochem. Soc. 105 (1958) 512.

[15] D.A. Harrington, B.E. Conway, Electrochim. Acta 32 (1987)

1703.

[16] R.D. Armstrong, M. Henderson, J. Electroanal. Chem. 39 (1972)

81.[17] L. Bai, D.A. Harrington, B.E. Conway, Electrochim. Acta 32 (1987)

1713.

[18] G.J. Brug, A.L.G. Van Der Eeden, M. Sluyters-Rehbach, J.H.

Sluyters, J. Electroanal. Chem. 176 (1984) 275.

[19] N. Krstajic, M. Popovic, B. Grgur, M. Vojnovic, D. Sepa, J.

Eletroanal. Chem. 512 (2001) 16.

[20] R. Simpraga, L. Bai, B.E. Conway, J. Appl. Electrochem. 25 (1995)

628.

[21] A. Lasia, A. Rami, J. Appl. Electrochem. 22 (1992) 376.

[22] L. Chen, A. Lasia, J. Electrochem. Soc. 138 (1991) 3321.

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