Reconciling Kinetic Dilemma in Photoelectrochemical Water Splitting via Mediating Small Polaron Hopping and Surface Water Oxidation

ABSTRACT Semiconducting oxides emerge as promising photoelectrodes for photoelectrochemical water splitting. However, the kinetic dilemma between ultrafast charge transport and sluggish surface reaction leads to their suboptimal activities. Here, we demonstrate a boron doping strategy that simultaneously enhances charge carrier transport and oxygen evolution reaction (OER) kinetics of bismuth vanadate (BVO) photoanodes. The cocatalyst‐free BVO photoanode, upon boron incorporation, shows a photocurrent density of 5.20 mA cm −2 and an applied bias photon‐to‐current efficiency (ABPE) of 1.69% at 1.23 and 0.6 V RHE , respectively. Spectroscopic characterizations and theoretical simulations collectively unravel the improved charge carrier transport and extraction kinetics with concurrently mediated small polaron hopping and trap states. Furthermore, the B‐BVO photoanode with potential formation of self‐assembled [B(OH) 4 ] − molecular configurations on its surface significantly accelerates the OER and achieves a cathodically shifted onset potential of 225 mV. Such modulations in BVO properties, particularly with mediated small polaron hopping and surface configurations, ameliorate the kinetic mismatch between charge transport and surface reaction, providing key insights for improving the intrinsic performance of most semiconducting oxides.