Fabrication of WO3/BiVO4 p-n Junction Photoanode for Efficient Solar Water Splitting

Abstract

Photo-electrochemical (PEC) water splitting for hydrogen production is one of the most attractive renewable energy technologies as it directly converts solar energy to chemical energy. And hence, it could play a central role in hydrogen-based energy economy of future. Efficient photo-catalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Hence, using single inorganic semiconductors faces a limitation and leads to decrease in overall efficiency of the PEC. Therefore, p–n junction photo-anodes can be very effective as they can facilitate the separation of the photo-generated electron–hole pairs. In this work, a p–n junction having n type WO3 and p type BiVO4 photo-anode has been designed and fabricated. This junction dramatically showed higher photocurrent density compared to individual WO3 and BiVO4 electrodes. We achieve one the highest photocurrent of 4.2 mA/cm2 at an potential of 1.23 V versus a reversible hydrogen electrode (RHE) under simulated sunlight without an added catalyst. In the composite WO3/BiVO4 film a shifted quasi-Fermi level results, due to electronic equilibration between the two materials. The better performance of WO3/BiVO4 hetero-junction electrodes is thus a consequence of the electron injection from BiVO4 into WO3, Thin layer (5 nm) of amorphous TiO2 was deposited on the photo-anode using electrochemical deposition. The deposition was noticed to be uniform and complete on the photo-anode and increases the photo-stability of the photo-anode for longer times. The strategies for constructing such kind of hetero-junctions are well applicable to other dual bandgap photo-anodes.