PCet

Proton-Coupled Electron Transfer (PCET) is a class of chemical reactions in which a proton and an electron are transferred between donors and acceptors in a coupled fashion. PCET processes can proceed through either a concerted mechanism, in which the proton and electron move in a single kinetic step, or through a stepwise sequence in which proton transfer occurs before or after electron transfer (PT-ET or ET-PT). PCET encompasses hydrogen-atom transfer (HAT) as a special case, but it also covers broader coupled transfers where the proton and electron move between different sites or in different solvent environments.

The driving forces in PCET are the redox potential and the acid-base properties of the proton donor and acceptor. The reaction coordinate often involves a network of hydrogen bonds and solvent reorganization, and the coupling between electronic and protonic degrees of freedom determines whether the process is concerted or stepwise. Theoretical descriptions frequently adapt Marcus theory to PCET and consider factors such as pKa differences, electrostatic coupling, and proton tunneling.

PCET is central to many biological and chemical processes. In biology, it governs charge transfer in photosynthesis and respiration, helping to manage energetics and minimize high-energy intermediates. In photosystem II and related enzymes, proton and electron transfers are coordinated to drive water oxidation and radical transport. In chemistry and materials science, PCET underpins catalytic oxidation and reduction reactions, fuel-cell relevant reactions, and the design of catalysts that employ proton relays and multi-site transfer pathways.

Experimental and computational studies continue to refine the understanding of PCET mechanisms, energetics, and practical applications in energy conversion and sustainable chemistry.