Coupling Ni3POM with FeOOH on BiVO4 Photoanodes for Efficient Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting provides a reasonable and feasible strategy to capture and transform solar energy, which employs a manner analogous to photosynthesis. Herein, a noble-metal-free polyoxometalate (K6Na[Ni3(H2O)3PW10O39H2O]·12H2O (Ni3POM)) as a novel molecular cocatalyst is incorporated into a typical FeOOH/BiVO4 composite photoanode for photoelectrochemical water splitting. Interestingly, we find that the combination of Ni3POM and the hybrid FeOOH/BiVO4 photoanode remarkably boosts the PEC performance. Particularly, the photocurrent density of Ni3POM/FeOOH/BiVO4 photoanode reaches 5.2 mA/cm2, causing an about 4-fold enhancement in the photoelectrochemical activity at 1.23 V vs RHE. Furthermore, the photocurrent density of the Ni3POM/FeOOH/BiVO4 photoanode still remains 99% after a 1 h stability test at 1.23 V vs RHE, indicating the PEC stability is greatly improved. Concomitantly, a 1.1% ABPE value was obtained at 0.8 V vs RHE. Notably, FeOOH not only is responsible for hole transfer between the POMs and BiVO4 but also plays a synergistic catalytic role with Ni3POM. The introduction of Ni3POM accelerates the separation and transfer of carriers and surface reaction kinetics, simultaneously improving the PEC stability. Our work may offer a strategy to design a novel molecular cocatalyst of POMs to promote PEC performance, further achieving efficient solar–fuel conversion.