Kinetics of Electrode Reactions

Abstract

One of the main peculiarities of a semiconductor electrode is the fact that the rate of an electrochemical reaction depends substantially on the electron structure of the semiconductor. In particular, this appears in the fact that electrons of the conductivity band and valence electrons may participate in the electrochemical reaction. Let us examine the electrode oxidation—reduction reaction

$${A^ + } + {e^ - } \rightleftarrows A$$

((24.1))

for the case where conductivity electrons participate in it. Let us denote the currents of the oxidation and reduction reactions by i_n ^c and i_n ^a, respectively. In analogy with metal electrodes (see, for example [1]) it is possible to write that the current i_n ^c is proportional to the number of the electrons at the contact n_s and to the number of ions in the electrolyte c_A+ and also to the probability of the transfer of an electron from the conductivity band to an ion [2–4]:

$$i_n^C = {k_1}{c_A} + {n_s}{e^{\frac{{\alpha F{\varphi _0}}}{{RT}}}}$$

((24.2))

where k₁ is the reaction rate constant, α is the transfer coefficient, φ ₀ is the potential drop in the Helmholtz layer,* and F is a Faraday.