Enhanced photoelectrochemical water oxidation on BiVO4 by addition of ZnCo-MOFs as effective hole transfer co-catalyst

Abstract

Solar-driven water splitting is one of greenways for massive conversion of sustainable and nonpolluting energy applied to meet global energy crisis. Photocatalysts are greatly explored to improve photoelectrochemical (PEC) water oxidation efficiency. Bismuth vanadate (BiVO4) has been extensively used as photocatalyst for water oxidation, but its passive oxygen evolution kinetics and charge carrier recombination lead to inferior PEC performance under light illumination. Tuning interfacial charge separation and transfer is an eminent way to stimulate water oxidation characteristics of BiVO4. Herein, a BiVO4/zinc cobalt metal-organic framework (ZnCoMOF) composite is firstly proposed as photocatalyst for water oxidation. ZnCoMOF nanosheets are loaded on BiVO4 surface as co-catalyst via solvothermal process. Effects of solvothermal duration and mole ratio of zinc and cobalt are investigated. The optimal BiVO4/ZnCoMOF electrode shows a photocurrent density of 3.08 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), which is 4.21 times greater than that of BiVO4 electrode. The redox properties of high valence metal ions in ZnCoMOF are used to store photoexcited holes and transfer them to the water oxidation process in the BiVO4/ZnCoMOF system. This work demonstrates that PEC performance of BiVO4 can be largely improved via controlling water oxidation kinetics and refining charge recombination and transport properties.