Boost proton transfer in water oxidation by constructing local electric fields on BiVO4 photoanodes

The slow-proton-fast-electron process severely limits the catalytic efficiency of oxygen evolution reaction. A method is proposed to accelerate proton transfer by building up local electric fields. Modifying acetic, ethanedioic and propanetricarboxylic (C₆H₈O₆) ligands on BiVO₄ surface results in a potential difference between BiVO₄ and ligands that generates a local electric field which serves as a driving force for proton transfer. Among the ligands, carrying the strongest electron-withdrawing ability, the modification of C₆H₈O₆ forms the strongest local electric field and leads to the fastest proton transfer and the smallest thermodynamic overpotential. C₆H₈O₆-BiVO₄ exhibits 3.5 times photocurrent density as high as that of pure BiVO₄, which is 3.50 mA cm^–2 at 1.23 V_RHE. The onset potential of C₆H₈O₆-BiVO₄ shifts negatively from 0.70 to 0.38 V_RHE. The mechanism for OER transitions from thermodynamically high energy proton-coupled electron transfer to thermodynamically low energy electron transfer as proton transfer is accelerated.