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

Abstract High-performance WO 3 /BiVO 4 heterojunction photoanodes were synthesized on a fluorine-doped tin oxide (FTO) substrate for photoelectrochemical (PEC) reduction of Cr(VI). Ultrathin BiVO 4 layer was deposited on the surface of the WO 3 photoanode using a drop-casting method. The WO 3 /BiVO 4 photoanodes were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, UV–vis spectrometry and photoelectrochemical measurements. The resulting WO 3 /BiVO 4 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/cm 2 at 2.2 V vs RHE with 200 μL BiVO 4 added, which is 4.6 times higher than that of the pristine WO 3 photoanodes. Then, the prepared WO 3 /BiVO 4 junction for the first time was applied in PEC reduction of Cr(VI). And it is found that the optimized WO 3 /BiVO 4 photoanodes show more excellent photoelectrochemical reduction of Cr(VI) than the individual WO 3 photoanode. In addition, PEC reduction of Cr(VI) by WO 3 /BiVO 4 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).