Photoelectrochemical reduction of Cr (VI) on plate-like WO3/BiVO4 composite electrodes under visible-light irradiation: characteristics and kinetic study

Abstract

High-performance WO3/BiVO4 heterojunction photoanodes were synthesized on a fluorine-doped tin oxide (FTO) substrate for photoelectrochemical (PEC) reduction of Cr(VI). Ultrathin BiVO4 layer was deposited on the surface of the WO3 photoanode using a drop-casting method. The WO3/BiVO4 photoanodes were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, UV–vis spectrometry and photoelectrochemical measurements. The resulting WO3/BiVO4 junction can efficiently broaden light absorption edge and facilitate the electron-hole pairs separation, leading to increase of photocurrent density. Specifically, the composite photoanodes yield a photocurrent density of 2.5 mA/cm2 at 2.2 V vs RHE with 200 μL BiVO4 added, which is 4.6 times higher than that of the pristine WO3 photoanodes. Then, the prepared WO3/BiVO4 junction for the first time was applied in PEC reduction of Cr(VI). And it is found that the optimized WO3/BiVO4 photoanodes show more excellent photoelectrochemical reduction of Cr(VI) than the individual WO3 photoanode. In addition, PEC reduction of Cr(VI) by WO3/BiVO4 electrodes was investigated with changing various factors such pH, the applied voltage, initial concentration and citric acid (CA) capture agent to determine the kinetic process for PEC reduction of Cr(VI).