Low-bias photoelectrochemical water splitting via mediating trap states and small polaron hopping

Metal oxides are promising for photoelectrochemical (PEC) water splitting due to their robustness and low cost. However, poor charge carrier transport impedes their activity, particularly at low-bias voltage. Here we demonstrate the unusual effectiveness of phosphorus doping into bismuth vanadate (BiVO₄) photoanode for efficient low-bias PEC water splitting. The resulting BiVO₄ photoanode shows a separation efficiency of 80% and 99% at potentials as low as 0.6 and 1.0 V_RHE, respectively. Theoretical simulation and experimental analysis collectively verify that the record performance originates from the unique phosphorus-doped BiVO₄ configuration with concurrently mediated carrier density, trap states, and small polaron hopping. With NiFeO_x cocatalyst, the BiVO₄ photoanode achieves an applied bias photon-to-current efficiency of 2.21% at 0.6 V_RHE. The mechanistic understanding of the enhancement of BiVO₄ properties provides key insights in trap state passivation and polaron hopping for most photoactive metal oxides.