Accelerated rates of proton coupled electron transfer to oxygen deficient polyoxovanadate-alkoxide clusters

Anionic dopants, such as O-atom vacancies, alter the thermochemical and kinetic parameters of proton coupled electron transfer (PCET) at metal oxide surfaces; understanding their impact(s) is essential for informed material design for efficient energy conversion processes. To circumvent challenges associated with studying extended solids, we employ polyoxovanadate-alkoxide clusters as atomically precise models of reducible metal oxide surfaces. In this work, we examine net hydrogen atom (H-atom) uptake to an oxygen deficient vanadium oxide assembly, [V6O6(MeCN)(OCH3)(12)](0). Addition of two H-atom equivalents to [V6O6(MeCN)(OCH3)(12)](0) results in formation of [V6O5(MeCN)(OH2)(OCH3)(12)](0). Assessment of the bond dissociation free energy of the O-H bonds of the resultant aquo moiety reveals that the presence of an O-atom defect weakens the O-H bond strength. Despite a decreased thermodynamic driving force for the reduction of [V6O6(MeCN)(OCH3)(12)](0), kinetic investigations show the rate of H-atom uptake at the cluster surface is similar to 100x faster than its oxidized congener, [V6O7(OCH3)(12)](0). Electron density derived from the O-atom vacancy is shown to play an important role in influencing H-atom uptake at the cluster surface, lowering activation barriers for H-atom transfer.