Inner-sphere proton-coupled electron transfers (PCETs) serve as key steps in many metal oxide-catalyzed energy conversion processes. While these PCET processes and the associated thermodynamics are often examined in an aqueous media, an equivalent understanding in a non-aqueous media is needed. The electrochemical response of a NiO electrode in acetonitrile in the presence of exogenous buffers demonstrates the one-electron/one-proton nature of the redox reactions. The presented Nernstian dependence of NiIIIOOH/NiII(OH)2 and NiIVO2/NiIIIOOH redox potential with respect to the buffer pKa can be converted to the corresponding O−H bond dissociation free energies (BDFEs). The derived BDFEs in acetonitrile were within 2 kcal/mol of those reported for similar electrodes in aqueous buffer. Furthermore, the derived Nernst equation can accurately describe the redox potentials over multiple buffers with different charges (i.e., cationic vs. anionic) or its capability to coordinate to the electrode surface, for example, via a carboxylate group. This solvent and buffer invariance is a novel and surprising result for heterogeneous materials. The importance of these BDFEs in an electrocatalytic context will be discussed.

Invariance of the surface O−H bond dissociation free energies of NiO electrodes with solvent, electrolyte, and buffer

ACS Spring Meeting 2021

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