Visualizing Overall Water Splitting on Single Microcrystals of Phosphorus-Doped BiVO₄ by Photo-SECM

Particulate bismuth vanadate (BiVO₄) has attracted considerable interest as a promising photo(electro)catalyst for visible-light-driven water oxidation; however, overall water splitting (OWS) has been difficult to attain because its conduction band is too positive for efficient hydrogen evolution. Using photoscanning electrochemical microscopy (photo-SECM) with a chemically modified nanotip, we visualized for the first time the OWS at a single truncated bipyramidal microcrystal of phosphorus-doped BiVO₄. The tip simultaneously served as a light guide to illuminate the photocatalyst and an electrochemical nanoprobe to observe and quantitatively measure local oxygen and hydrogen fluxes. The obtained current patterns for both O₂ and H₂ agree well with the accumulation of photogenerated electrons and holes on {010} basal and {110} lateral facets, respectively. The developed experimental approach is an important step toward nanoelectrochemical mapping of the activity of photocatalyst particles at the subfacet level.