Proton-Coupled Electron Transfer (PCET) chemical reactions involve movement of electron(s) and proton(s). Many processes involve PCET, including energy conversions in fuel cells and the mitochondrial electron transport chain, chemical processes in the environment, and recent applications in organic synthesis and nanochemistry. Every science student learns that a hydrogen atom is a proton and an electron (H• = H+ + e–) but there are broad implications of that simple statement. Hydrogen atom transfer (HAT) is perhaps the simplest kind of PCET, where the H+ and e– transfer ‘together,’ whatever that means for two quantum particles. PCET can also involve H+ and e– that are separated in space and/or in time.
The second lecture will explore how PCET reactions can and cannot be described by linear free energy relationships (LFERs). More generally, it will develop the often-ignored issues in applying molecular LFERs to interfacial reactions. For instance, X–H molecules have a single bond dissociation free energy (BDFE), on many surfaces there are wide distributions of surface–H structures and BDFEs. These results lay groundwork to understand H on complex surfaces, which is central to heterogeneous catalysis, electrocatalysis, and other technologies.