Electrode redox reactions with polarizable molecules.

Area of Science:

• Physical Chemistry
• Electrochemistry
• Theoretical Chemistry

Background:

• Classical theories of interfacial electrochemistry do not account for molecular polarizability changes during electron transfer.
• Existing models like the Marcus formulation use a single parameter, potentially limiting accuracy for redox reactions.

Purpose of the Study:

• To formulate a new theory for redox reactions involving electron transfer between a metal electrode and a polarizable molecule.
• To incorporate molecular polarizability and its change during electron transfer into a theoretical framework.
• To develop a more accurate model for electrode electron transfer reactions.

Main Methods:

• Formulation of a theory for redox reactions considering electron transfer and molecular polarizability.
• Modeling electron transfer as crossing two non-parabolic free energy surfaces.
• Derivation of an analytical solution for free energy surfaces and activation barriers.

Main Results:

• The theory predicts non-Gaussian statistics for thermal fluctuations when polarizability differs between oxidized and reduced states.
• The activation barrier is defined by two reorganization energies, contrasting with the single parameter in Marcus theory.
• The model predicts asymmetric cathodic and anodic current branches with different slopes and curvature compared to Marcus-Hush and Butler-Volmer models.

Conclusions:

• The new non-Gaussian theory provides a more comprehensive description of electrode electron transfer by including molecular polarizability.
• The theory's predictions align with the Nernst equation and offer insights into the asymmetry of electrode currents.
• This work advances the understanding of interfacial electron transfer mechanisms and their kinetics.