Tuning Selectivity of Photoelectrochemical Water Oxidation via Facet-Engineered Interfacial Energetics

Water oxidation kinetics has been identified as the bottleneck of the solar water splitting reaction for H2 production. Herein, we demonstrate that even for crystal facets with the same thermodynamically favorable pathway for water oxidation, the interfacial energetics formed by the terminated facet/electrolyte interface can significantly regulate the water oxidation kinetics to tune the product selectivity. Specifically, we elucidate that the (010) facet of the BiVO4 photoanode can offer suitable band bending and deep valence band level to produce high-value-added hydrogen peroxide (H2O2) with an average Faradaic efficiency of 70% from water oxidation. This simple strategy without other modifications can lead to a 30-fold increase in the applied bias photon-to-current efficiency of photoelectrochemical water splitting. This study sheds new light on the crystal facet effect beyond the erstwhile focus on charge separation and transfer and offers a new opportunity to enhance the solar-to-H2 efficiency.