Photoactivity and Stability of WO3/BiVO4 Photoanodes: Effects of the Contact Electrolyte and of Ni/Fe Oxyhydroxide Protection

Photoelectrodes with the WO3/BiVO4 heterojunction architecture are among the most efficient semiconductor oxide-based photoanodes for water oxidation. However, because of the different experimental conditions employed in their photoelectrochemical characterization (in particular the nature and concentration of the contact electrolyte and the pH of the solution), a direct and unambiguous comparison of their performance obtained in different labs is often quite difficult. In this work, we systematically tested identical WO3/BiVO4 photoanodes in contact with solutions of the most commonly used electrolytes, i.e. Na2SO4 and the potassium phosphate buffer (KPi), at various electrolyte concentration and pH. Furthermore, WO3/BiVO4 photoanodes protected with a Ni/Fe oxyhydroxide oxygen evolution catalyst were also tested under identical conditions. In contact with KPi solutions, both unprotected and protected electrodes produce higher photocurrent than in contact with Na2SO4 solutions, but they proved to be less stable, particularly under basic conditions. WO3/BiVO4 heterojunction systems modified by deposition of the Ni/Fe oxyhydroxide co-catayst proved to be more stable and to produce higher photocurrent, with a cathodic shift of the photocurrent onset.