Pivotal synergistic role of surface trapping states regulation of bismuth vanadate photoanodes and hydrazine oxidation in water splitting

Abstract

The kinetic restriction on charge transfer at the semiconductor/electrolyte interface has become a major problem which limits bismuth vanadate (BiVO4) as a promising solar water splitting material. Herein, we regulate the surface trapping state by covering the Al2O3 layer, and replace the slow oxygen evolution reaction with the thermodynamically favorable hydrazine oxidation, finally realizing efficient hydrogen production. The Al2O3 layer alters the surface state charge, so the surface recombination centers of the BiVO4 photoanode are passivated by the Al2O3 layer, which inhibits the reversible redox process of V4+/V5+ and also prevents the irreversible surface conversion from electron capture VO2+ to VO2+, achieving a surface charge transfer efficiency (ηsur) of 62 %, compared with 28 % of BiVO4. Meanwhile, the photocurrent of the hydrazine-assisted Al2O3/BiVO4 photoanode reaches 4.10 mA cm−2 at 1.23 VRHE, which is 4.18 times that of bare BiVO4. The onset potential is lowed to −0.04 V, which is 370 mV negative shift compared to pure BiVO4 because the hydrazine oxidation reaction can hugely decease the onset potential. This work provides a new strategy for combination of passivator for the effective suppression of surface states and the replacement of water oxidation with thermodynamically more favorable oxidation reactions for efficient photoelectrochemical water splitting.