Electrochemical reactions with protonations at equilibrium: Part VI. The homogeneous electron exchange reaction between a monoelectronic and A 1 e, 1 H+ system

The rate of homogeneous electron exchange between a 1 e redox couple and a 1 e, 1 H⁺ redox system is studied theoretically when the protonations are much faster than the electron exchange reactions, i.e. when they can be assumed to be at equilibrium. It is shown that the whole system is equivalent to a reaction between two simple 1 e couples, with apparent rate constants for the electron exchange. Variations of these constants are complex functions of the difference of the standard potentials of the monoelectronic system and those of the 1 e, 1 H⁺ system. They also vary with pH in a less complicated way. The reaction path and the reaction sequence (order of addition or loss of electrons and protons) are studied. A potential-pH diagram, which allows the results to be visualized, is given. It is shown that it is not possible to accelerate at the same time the reduction and oxidation of the members of the square scheme by the same monoelectronic system. Applications to redox polymer electrodes are discussed.