Redox−Acid/Base Phase Diagrams as an Entry to Computational Redox Chemistry

The rapid depletion of fossil fuels and the change from conventional energy supply to so-called sustainable and renewable energy sources have led to a renaissance of electrochemical, photochemical, and photoelectrochemical methods for chemical synthesis. While drastic experimental improvements have been realized in recent years, systematic computational studies of these types of reactions are, however, rather limited caused by a lack of suitable representations. Herein we present a generalized method to investigate and analyze a chemical system with respect to its redox- and acid/base-properties based on Gibbs free-energy differences. We represent the results in a clear manner by means of redox−acid/base phase diagrams. Motivated by computational needs, the presented method is a direct link between experimentally measurable values and Gibbs free-energy profiles, connecting experiment and simulation. Thus, it serves as an entry to systematic computational studies of reactions, which involve a combination of electron transfers and acid/base-chemical reaction steps, because it enables the representation of both thermodynamic and kinetic properties. The presented method is applied to four exemplary systems: Phenol, dicobaltocenium amine as a proton-coupled electron transfer (PCET) reactant, and two porphyrin Ni^II catalysts for the electrocatalytic hydrogen evolution reaction (HER).