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

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 similar to 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)).