The rate of decay of hydrogen and oxygen overvoltages

Armstrong, Graeme D.; Butler, J. A. V.

doi:10.1039/tf9332901261

Cited by 42 publications

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“…[10] ioF The quantity r represents physically the degree of reversibility of the reaction considered and the potential drop across this reaction resistance when a current i is passed is simply the overpotential ~1 ir = io =,1 [11] Under the conditions specified above, the electrode acts as a series combination of a capacitor (equal in value to the sum of the d.1. capacitance [assumed relatively negligible] and the adsorption pseudocapacitance) and a resistor, as shown schematically below ( Fig.…”

Section: Fig 1 Equivalent Circuit For Charging the Pseudocapacitancmentioning

confidence: 99%

“…An alternative group of methods, widely used to determine the total capacity at the metal solution interphase, depends on the relation i ~ C (dV/dt) [3] in which i is the direct current used to charge the capacitance C. Constant current charging curves (taken over an interval of potential where the part of the current used for the relevant over-all Faradaic process is negligible) have been used by Frumkin et al (10) and by Butler (11), and the method has since become a generally used technique. Initial rates of decay of overpotential on open-circuit have also been used (12,13) to determine C. This method is based on the assumption that the electrode reaction continues on open-circuit by a self-discharge process which momentarily, at the commencement of the open-circuit transient, has the same rate as that corresponding to the steady-state polarizing current density.…”

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confidence: 99%

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Significance of Nonsteady-State A-C and D-C Measurements in Electrochemical Adsorption Kinetics

Conway¹,

Gileadi

Angerstein‐Kozlowska³

1965

J. Electrochem. Soc.

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Information obtainable from nonsteady-state electrochemical studies is examined with particular reference to the determination and significance of capacitance associated with adsorbed intermediates in consecutive reactions. The frequency dependence of the capacity in a-c measurements is related to the rise-time dependence in d-c charging transients and the concept of an equivalent frequency in d-c measurements is proposed. The nonsteady-state kinetics for a galvanostatic charging process is examined for a reaction sequence involving adsorbed intermediates, and it is shown how the capacitance behavior depends on the charging current density. Applications to the triangular voltage sweep method are made, and it is shown that for this case where neither steady-current nor steady-state kinetics apply, care must be exercised in interpretation of results derived from this method. The nonsteady-state kinetics for this case are derived and the dependence of the capacity on sweeprate is deduced. The differential galvanostatic method leads to results which can be much more explicitly analyzed in a rigorous kinetic manner, for irreversible charging processes. Applications to experimental results which support the treatment given are discussed.The adsorption pseudocapacitance (1) arising in certain electrochemical reactions, where an initial discharge step is at quasi-equilibrium when followed by a rate-determining step, may be defined aswhere 0 is the fractional surface coverage by intermediates formed by the discharge of an ionic species, V is the metal-solution potential difference, and k is a proportionality constant, representing the Faradaic charge which has to cross the metal-solution interface for a complete monolayer of discharged species (e.g., adsorbed radicals, metal adions) to be formed on unit real surface area of the electrode.Experimental methods for determining the adsorption pseudocapacitance have been reviewed recently (2-4) and the form of the C --V relationship has been derived, assuming that the electrode system obeys an ideal Langmuir isotherm (5, 6) and for the more general and experimentally applicable case when the variation of the heat of adsorption with coverage (Temkin type of isotherm) is also taken into account (1, 7). Cases for which the assumption of quasi-equilibrium in the initial ion discharge step cannot be made have also been considered (7,8).The capacitance at the metal-solution interface can be obtained from a-c impedance determinations by a compensating bridge method or from phase angle measurements. The electrode is first polarized to a steady-state by applying a constant current or potential, and its impedance with respect to a small a-c signal is measured and resolved into its capacitative and resistive components. The amplitude of the a-c signal is maintained very low so that the steady current condition at the electrode is not significantly disturbed. The capacitance measured by the method is usually found to depend on the frequency and at any frequency it is the sum of the ionic ...

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Section: Fig 1 Equivalent Circuit For Charging the Pseudocapacitancmentioning

confidence: 99%

mentioning

confidence: 99%

Significance of Nonsteady-State A-C and D-C Measurements in Electrochemical Adsorption Kinetics

Conway¹,

Gileadi

Angerstein‐Kozlowska³

1965

J. Electrochem. Soc.

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“…The self-discharge rates are increased substailtially by increasing KOH activity (Figs. 8, 9); hence process [9] is unlilcely to be rate-determining, since with increasing I<OH activity from 0 to 15 M, the water activity falls from unity to about 0.2 (8). Some step in the ailodic oxygen evolution process in self-discharge is therefore rate-determining (cf.…”

Section: Reaction Mechanisms In the Self-discharge Processmentioning

confidence: 99%

The Electrochemical Behavior of the Nickel – Nickel Oxide Electrode: Part I. Kinetics of Self-Discharge

Conway¹,

Bourgault²

1959

Can. J. Chem.

127

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The nickel -nickel oxide electrode forms the positive plate in the charged nickel-cadmium battery. After "charging" the electrode t o a chemical state represented by the non-structural formula NiO,, where x can vary from about 1.4 to 1.8 depending on the current density and temperature, loss of oxygen and a fall of potential on open circuit occurs. In the present work this "self-discharge" effect has bee11 examined by study of (i) the rate of decay of e.m.f. on open circuit, (ii) rate of oxygen e v o l u t i o~~ on open circuit, (iii) the electrochemical capacity of the electrode, and (ill) the build-up or charging curves for the electrode. The decay behavior has been studied in aqueous ICOH solutions from 0.0015 to 15 M. Tafel slopes are obtained from the plots of e.m.f. vs. log (time of decay), and abrupt changes occur a t certain electrode potentials which indicate changes of rate-determining mechanism in the self-discharge process. The slopes observed are interpreted in terms of a new scheme of consecutive reactions for anodic oxygen e v o l u t i o~~ by deducing, by nleans of the Christiansen method, the relevant Tafel slopes. I t is shown that the scheme proposed uniquely accounts for the esperimental behavior and that the change of mechanism observed in the self-discharge can only be explained if two consecutive and not alternative processes are irlvolved. The dependence of the rates of self-discharge upon OH-ion and water activity is deduced and the significance of these results is discussed. INTRODUCTIONInterest in the behavior of the nickel -nickel oxide electrode arises from its use as the positive plate in the nickel-cadmium and nickel-iron batteries; a t the same time, study of the system affords further insight into the fundamental kinetics of anodic processes, which in the case of the nickel system are complex owing to the existence of several possible oxidation states of the metal in corresponding hydrated oxides (1, 2). One of the features of interest is the loss of charge of the nickel oxide electrode when it is left standing in pure alkaline solution on open circuit. T h e loss of charge is accompanied by oxygen evolution and decay of e.m.f. of the electrode (e.g., measured with respect to the Hg/HgO electrode in the same s o l u t i o~~) .Hitherto, studies of the kinetics of decay have not been made rigorously and only sorneu~hat arbitrary rate measurements have been obtained (i) by determining the total time required for the e.m.f. of the electrode to decay over about 0.G v (3), and (ii) by determining the total volume of oxygen liberated from an electrode a t the end of a period of 13 hours (4). Since it is clear that over the potential range studied (3) more than one process is involved in the decay, because the e.m.f.-time curve passes through an inflection, and since in the oxygen evolution process (4) the rate of oxygen evolution depends on the electrode potential, it must be concluded that the kinetic significance of "rates" measured by these procedures is unclear. Furthermore,...

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“…decay are normally expressed (8,11,12) by an equation, a t any potential (where b is the ~a~e r i a i l Tafel slope), and ioeVlb is, in fact, the selfdischarge current passing a t the potential V; it is clear then (as we show elsewhere (10)) that CV can be obtained a t any potential in the decay curve if the corresponding Tafel expression is known over the same range of potentials, since the Tafel equation defines the term ioevlb a t any potential. In this discussion, it is assumed, as usual (8,11,12), that on open circuit the same process as that during steady polarization is the ratedetermining one. The charge associated with the capacity CV is hence obviously where we keep the term dV/dt in the denominator for convenie~ice in order to evaluate io exp [V/b]/dV/dt experimentally and integrate the result over a range of values of V. The value of Aq obtained is obviously that corresponding to the change of q over the potential range V1 to 112.…”

Section: Iiij the Charge And Pseudocapacity Associated With Adsorbed mentioning

confidence: 99%

New Approaches to the Study of Electrochemical Decarboxylation and the Kolbe Reaction: Part Iii. Quantitative Analysis of Decay and Discharge Transients and the Role of Adsorbed Intermediates

Conway¹,

Dzieciuch²

1963

Can. J. Chem.

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Galvanostatic cathodic discharge and open-circuit decay transients have been obtained for the decarboxylation of formate in formic acid and interpreted quantitatively in terms of ' the adsorption of intermediates in the reaction. These intermediates are identified with HCOO' radicals. Extended anodic polarization a t platinum and particularly a t palladium leads to the formation of films of a n anodic product which are considerably thicker than a inonola>er. After relatively long tiines ( > 100 seconds) of anodic polarization, the film growth obeys the inverse logarithmic rate law deduced by Mott and Cabrera. The thick films which are formed a t palladium are believed t o be responsible, upon autocatalytic decomposition, for the delayed gas evolution phenomenon observed a t this metal.X new method for deduction of adsorption pseudocapacitance and charge associated with the ad-layer from open-circuit decay curtes and Tafel parameters is used to obtain the pseudocapacitance and charge associated with the transition region in the current-potential curves for the formate decarbox>lation. I t is shown that this region corresponds to filling of the surface n ith adsorbed intermediates formed in the reaction. These observations are shown to support the reaction mechanism proposed in Part I.

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The rate of decay of hydrogen and oxygen overvoltages

Cited by 42 publications

References 0 publications

Significance of Nonsteady-State A-C and D-C Measurements in Electrochemical Adsorption Kinetics

Significance of Nonsteady-State A-C and D-C Measurements in Electrochemical Adsorption Kinetics

The Electrochemical Behavior of the Nickel – Nickel Oxide Electrode: Part I. Kinetics of Self-Discharge

New Approaches to the Study of Electrochemical Decarboxylation and the Kolbe Reaction: Part Iii. Quantitative Analysis of Decay and Discharge Transients and the Role of Adsorbed Intermediates

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