Recent Advances in Mediator and Proton Relay Usage in Molecular Catalysis

Electron-proton transfer mediators (EPTMs), redox mediators (RMs), and proton relays (PRs) have been incorporated into diverse homogeneous molecular catalysts to enhance catalytic efficiencies in the reactions of energy-related small molecules (e.g., CO₂, O₂,H₂O, and N₂) and organic compounds. However, the benefits of using EPTMs, RMs, and PRs in molecular catalysis have not been comprehensively or quantitatively benchmarked. This review highlights the latest developments in this field, focusing on the kinetics, thermodynamics, and selectivities of multiple proton-electron redox processes, as well as their corresponding advantages. The reaction mechanisms, linear free energy relationships, and catalytic Tafel plots are considered to provide a solid foundation for evaluating these catalytic systems and the strategic development of molecular catalysts. These efforts are expected to advance the application of molecular catalysis in energy conversion and sustainability.