It is increasingly recognized that many redox reactions at metal oxide/solution interfaces occur by proton-coupled electron transfer (PCET). In many cases (but not all), these reactions involve the transfer of equal numbers of protons and electrons, or in other words the net transfer of hydrogen atoms. We have been studying a variety of materials including nickel oxide electrodes and ceria, titania, and zinc oxide nanocrystals. We aim to understand their PCET stoichiometry, thermochemistry, kinetics, and catalysis. The number of H atoms that can be added to or removed from an oxide surface — the surface coverage — varies substantially with the material, its morphology, and the state of the surface. Surface O–H bond dissociation free energies (BDFEs) have been measured electrochemically, by equilibration with soluble PCET reagents, and computationally. Some oxide materials have a single, well-defined BDFE, while others exhibit a range of BDFEs depending on the hydrogen surface coverage. Initial observations are providing insights into how the nature of the material, the hydrogen surface coverage and bond strengths, all affect the kinetics of PCET reactions and related electrocatalytic processes.

Proton-coupled electron transfer at metal oxide-solution interfaces

ACS Spring 2022

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