Low-cost Preparation of WO₃/BiVO₄ Nanocomposite Photoanodes for Photoelectrochemical Water Oxidation

Abstract Nanostructured WO3 electrodes coated with BiVO4 are known to be among the best performing BiVO4-based photoanodes for photoelectrochemical water splitting. However, record performance is only achieved using intricate and costly electrode fabrication processes; when lower-cost, more scalable methods are used, performance drops significantly. Here, we show that a low-cost successive ionic layer adsorption and reaction method, which has received relatively little attention for the preparation of BiVO4, can be used to convert nanoporous WO3 films prepared by spin coating into high-performance WO3/BiVO4 photoanodes. After treatment with a cobalt phosphate co-catalyst, optimized WO3/BiVO4 photoanodes can reach water oxidation photocurrent densities of up to ~3.4 mA cm-2, with a photocurrent onset potential of ~0.56 V vs. RHE. Furthermore, an investigation by impedance spectroscopy showed that the electron diffusion length in both types of film is longer than the film thickness, which is an important requirement for an efficient nanostructured electrode. These results highlight the role that simple deposition methods such as SILAR can play in the preparation of nanocomposite photoanodes for PEC applications.