Surface defects engineering of BiFeO3 films for improved photoelectrochemical water oxidation

As a promising material for photoelectrochemical (PEC) water oxidation, the fast recombination rate and slug-gish surface reaction for BiFeO3 (BFO) still hinder its practical application. In this work, nitrogen plasma was first used to engineer surface defects of the pulsed laser deposition (PLD)-fabricated BFO films to suppress the surface charge recombination and improve the surface water oxidation activity, as well as enhance the stability. A remarkable photocatalytic activity enhancement was observed after the surface modification. Specifically, the photocurrent density is 95 mu A/cm2 at 0.6 V (vs. Ag/AgCl, pH=12.8) for BFO-N (after nitrogen plasma treat-ment), which is about 8 times higher than as-grown BFO (12 mu A/cm2) at the same potential. Meanwhile, the onset potential of BFO-N shifts toward the negative value by 120 mV compared to BFO. Also, the BFO-N reveals superior stability to BFO, which shows nearly no decay after the 1-h test. Complete experimental characterization and deep mechanistic analysis indicate that the enhanced performance could be due to the newly-formed Fe -enriched oxynitride layer on the surface after nitrogen plasma treatment, which suppresses the fast recombi-nation, improves the water oxidation reaction kinetics, and protects the photoanode against photocorrosion. Our work offers a simple, but effective way to improve the PEC performance of BFO, which is instructive for fabri-cating similar high-performance photoelectrodes for PEC applications.