Proton-coupled electron transfer (PCET) reactions play an important role in a wide range of energy conversion processes. This talk will focus on theoretical studies of electrochemical PCET reactions, which occur by sequential or concerted mechanisms. A general theoretical formulation for PCET is utilized to examine the mechanisms and calculate the electrochemical rate constants. This theory includes the quantum mechanical effects of the active electrons and transferring proton, as well as the motions of the proton donor-acceptor mode and solvent. Applications to molecular electrocatalysts for hydrogen production will be discussed, including cobalt complexes with diglyoxime ligands and nickel complexes with pedant amines to facilitate a proton relay. The thermodynamically favored pathways are identified for each catalyst, and the electrochemical rate constants are calculated as functions of the overpotential. The impact of substituents on the mechanisms and electrochemical rate constants is also investigated. In addition, recent developments of theoretical approaches for simulating the ultrafast dynamics of photoinduced PCET will be discussed. These calculations provide insights into the roles of proton vibrational relaxation and nonequilibrium solvent dynamics in photoinduced PCET processes.
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