Quantum Electrochemistry: New Aspects in Electrochemistry and Electrocatalysis

Abstract

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.

Viologen Hydrothermal Synthesis and Structure–Property Relationships for Redox Flow Battery Optimization

“…For symmetric viologens, those of smaller functionalization size demonstrated more facile redox rate kinetics, which is hypothesized to be due to less shielding of the redox active aromatic core from the electrode surface. [ 22 ] Interestingly, the asymmetric derivatives displayed higher rate constants than the symmetric counterparts. Although electrode double layer dynamics are complex and require detailed theoretical and spectroscopic study, we hypothesize that the asymmetric geometry prevents tight, ordered packing between viologens and instead encourages increased entropy towards overcoming free energy activation barriers at the electrode surface.…”

Viologen Hydrothermal Synthesis and Structure-Property Relationships for Redox Flow Battery Optimization

“…For symmetric viologens, those of smaller functionalization size demonstrated more facile redox rate kinetics, which is hypothesized to be due to less shielding of the redox active aromatic core from the electrode surface. 23 Interestingly, the asymmetric derivatives displayed higher rate constants than the symmetric counterparts. Although electrode double layer dynamics are complex and require detailed theoretical and spectroscopic study, we hypothesize that the asymmetric geometry prevents tight, ordered packing between viologens and instead encourages increased entropy towards overcoming free energy activation barriers at the electrode surface.…”