Incorporation of oxidized zeolitic imidazolate framework 67 as effective Co-catalyst on W-doped BiVO₄ for catalyzing photoelectrochemical water oxidation

Bismuth vanadate (BiVO₄) with suitable conduction/valence band edges and band gap has been largely applied on photoelectrochemical catalytic water oxidation as clean energy technology. To solve the short charge diffusion length and poor water oxidation kinetics of BiVO₄, it is useful to dope heteroatoms and decorate co-catalysts for improving its catalytic ability and electricity. Oxidized zeolitic imidazolate framework 67 (ZIF67) with polyhedron structure and possible composition of cobalt oxide is highly attractive as co-catalyst of BiVO₄. In this study, it is the first time to decorate oxidized ZIF67 (O67) as co-catalyst on W-doped BiVO₄ (WBVO) using the drop casting technique for catalyzing photoelectrochemical water oxidation. Different amounts of ZIF67 are decorated on WBVO using the drop-casting technique. The O67 is merged into WBVO nanorod arrays after converting ZIF67 into O67 using the annealing process. The highest photocurrent density of 2.08 mA/cm² at 1.23 V versus reversible hydrogen electrode (V_RHE) is obtained for the optimal WBVO/O67 electrode in the electrolyte without hole scavenger, while the WBVO electrode only shows the photocurrent density of 1.20 mA/cm² at the same condition. The decoration of O67 can increase light absorption, generate active sites, and reduce charge recombination. The photocurrent retention higher than 92% is achieved for the WBVO/O67 electrode under continuous illumination for 5000 s. The greatly enhanced photoelectrochemical catalytic ability of WBVO/O67 implies the feasibility of utilizing oxidized ZIF67 as a co-catalyst to accelerating water oxidation.