The problem of correction for ohmic potential drop in linear potential sweep experiments and the derivation of s0 values for electrode surface processes
✍ Scribed by D.F. Tessier; B.E. Conway
- Publisher
- Elsevier Science
- Year
- 1985
- Tongue
- English
- Weight
- 710 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
Rate constants or exchange current densities of electrode surface processes involving a&tom arrays are conveniently evaluated by determining that sweep rate, s0 (the reversibility parameter), in a linear potential sweep (LPS) experiment, below which the process just remains kinetically reversible, ie its overpotential is sensibly zero. Transition to irreversibility is characterized by pealc potentials, E,, becoming linear in the log of the sweep rate, s, following a region of independence of s for s < sO_ A suitable extrapolation procedure enables se to be evaluated. However, if s,, is large and/or the resistivity of the solution is appreciable. the IR. drop associated with uncompensated resistance in the measurement system can be comparable with the increase of E, with logs, when s r s,,, rendering evaluation of s0 inaccurate. While compensation or empirical correction for this may be made, it is desirable that the nature of the IR, effect on the LPS I vs E profiles be understood in a more fundamental way. It is the purpose of this communication to provide such a treatment of this effect through evaluation of the actual timedependent potential that becomes applied to the electrode, and to proposecriteria based on the product of s,, , R, and the reaction pseudocapacitance, C, for indicating the anticipated extent of the IR, effect in the evaluation of s,, While the transition in the gP us logs plot may be due to IR, effects as well as to kinetic irreversibility, when the former are appreciable, tt is shown that the corresponding transition in the value of C, with increasing log s cm usually allow spurious IR, and significant irreversibility effects to be distinguished.