Ultrathin FeOOH nanosheets as an efficient cocatalyst for photocatalytic water oxidation

Water oxidation is a crucial step in photocatalytic water splitting and CO2 reduction with H2O, but is generally hindered by slow kinetics. Herein, ultrathin FeOOH nanosheets (FeOOH NSs, 1.8 nm) with abundant oxygen vacancies are composited with BiVO(4)via an electrostatic adsorption method, and the resulting composite demonstrates a remarkable enhancement in visible-light photocatalytic and photoelectrochemical oxygen evolution, approximately 2-fold and 9-fold higher than that of pristine BiVO4, respectively. The kinetics study shows that FeOOH NS loading leads to a 90% decrease in apparent activation energy compared to that of pristine BiVO4. The prominent cocatalyst effect of FeOOH NSs is further validated in RhB degradation with an 8-fold apparent rate constant enhancement. Effective charge carrier separation and transfer are clarified by photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) characterization. The oxygen vacancies, systematically studied by X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and extended X-ray absorption fine structure (EXAFS) characterization, are experimentally and theoretically demonstrated to be crucial for facilitating photocatalytic water oxidation.