Solution-processed yolk–shell-shaped WO3/BiVO4 heterojunction photoelectrodes for efficient solar water splitting

Abstract

The WO₃/BiVO₄ heterojunction is regarded as one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting. To improve the solar water splitting efficiency, maximizing the solar light absorption efficiency in a photoelectrode is still a critical issue. Here, to achieve the aforementioned need, we designed and fabricated a WO₃ film consisting of yolk–shell structured nanoparticles via solution processing. A thin BiVO₄ layer with a smaller bandgap was coated onto the surface and inside the WO₃ shells, providing a rationally designed inner space between the particles and the shell for better electrolyte accessibility. The yolk–shell-shaped PEC photoanode not only induces efficient light absorption but also plays an important role in electron collection from BiVO₄ due to an enlarged contact area. The structure–PEC performance relationship was studied by combining ultraviolet-visible (UV-vis) absorption spectroscopy with a specular and diffuse reflectance technique, which illustrates that the yolk–shell morphology has a superior light absorption ability than conventional hollow or dense film structures. The pure yolk–shell (Y-WO₃/BiVO₄) photoanode possessed a photocurrent density of 2.3 mA cm⁻² and achieved a highest value of ∼5.0 mA cm⁻² after adding a Fe–Ni co-catalyst at a bias of 1.23 V vs. RHE under AM 1.5 illumination (100 mW cm⁻²).