A novel Cl^- modification approach to develop highly efficient photocatalytic oxygen evolution over BiVO₄ with AQE of 34.6%

Water oxidation with multielectron transfer is regarded as the crucial step in photocatalytic water splitting. However, a facile but efficient method to promote its slow kinetics is still highly demanding. This work demonstrates that Cl^- surface modification drastically enhances photocatalytic water oxidation over BiVO₄ as well as WO₃. The optimal modified BiVO₄ achieves a photocatalytic activity of 4.2 orders enhancement relative to the pristine BiVO₄, giving up to an excellent apparent quantum efficiency of 34.6% at 420 nm. Cl^--modified 30-facet BiVO₄ with 2.6 times enhancement confirms that the surface reaction involved with photogenerated holes can be dramatically accelerated by Cl^- modification in addition to enhanced charge carrier separation. Our results highlight the impact of Cl^- modification on the reaction kinetics and pathway during the photocatalytic water oxidation process, which has been mostly overlooked. Systematic studies (DFT simulations, kinetic experiments) reveal that Cl^- modification remarkably reduces the photocatalytic water oxidation energy barrier and alters reaction pathway, which is also manifested in facilitated H₂O molecule activation in synchronous illumination XPS (SI-XPS) study. The EXAFS and angle-resolved XPS (AR-XPS) results show that Cl bonds to Bi and mainly concentrates on the surface of modified BiVO₄. Our findings provide an effective and facile approach to exploring efficient O₂ evolution semiconductors for photocatalytic water splitting.