Size effects of zeolitic imidazolate framework 67 polyhedrons as Co-catalyst of W-doped BiVO4 electrodes for photoelectrochemically catalytic water oxidation

Co-catalyst decoration and heteroatom doping techniques are largely applied to enhance photoelectrochemical catalytic ability of BiVO4. Zeolitic imidazolate framework 67 (ZIF67) with cobalt center and high specific area is promising as co-catalyst of BiVO4. In this study, it is the first time to synthesize different sizes of ZIF67 polyhedrons as co-catalyst of W-doped BiVO4 (WBVO) using electrodeposition and hydrothermal techniques to catalyze water oxidation. Decorating ZIF67 on WBVO (WBVO/ZIF67) can enhance light absorption intensity, create active sites, and suppress recombination to improve water oxidation kinetics. The highest photocurrent density of 2.30 mA/cm2 at 1.23 V versus reversible hydrogen electrode (VRHE) is obtained for WBVO/ZIF67 electrode with the smallest size of ZIF67 in electrolyte without hole scavenger, while the WBVO electrode only presents the photocurrent density of 0.9 mA/cm2 at the same condition. The smallest size of ZIF67 can provide largest contacts with WBVO and electrolyte and create efficient charge transfer paths and numerous active sites. The photocurrent retention higher than 80% is achieved for WBVO/ZIF67 electrode under continuous illumination for 5000 s. The highly improved photoelectrochemical catalytic ability of WBVO/ZIF67 confirms the feasibility of applying ZIF67 as co-catalyst and indicates the significance of sizes of ZIF67 co-catalyst on catalytic ability.