Quantum Electrochemistry: New Aspects in Electrochemistry and Electrocatalysis

Quantum mechanical theory of electrochemical kinetics based on Fermi’s golden rule was formulated by introducing the concept of electron transfer distance. The expressions for the exchange current density and standard rate constant in electrochemistry were derived in analytical form, as well as exponential current overpotential dependence. The theory corresponds well to the electrode kinetics based on the transition state theory. It was applied to various kinds of electrode reactions to analyze the standard rate constants and the exchange current densities reported in past literature. The evaluated magnitudes of the electron exchange energy were very small, being in the order of 10−3 eV–10−5 eV. A new theory of transfer coefficient was constructed based on Debye-Hückel theory for electrolyte solutions could explain quantitatively the dependence of the transfer coefficient on the ionic strength of electrolyte solutions. It was demonstrated that the transfer coefficient represents electrostatic screening of the electrode potential by ions near the electrode and its magnitude was calculated quantitatively. Electron transfer distance was obtained by analyzing the dependence of the transfer coefficient on the ionic strength of electrolyte solutions. Our theory supported the ordinary electron transfer mechanism due to the overlap of wave functions between the electrode and redox species, denying tunneling mechanism.