Three-dimensional WO₃ nanorod arrays on Si as photoanodes for efficient photoelectrochemical water splitting

Arrays of WO₃–Si forest hierarchical structures have been successfully synthesized by growing WO₃ nanorod on the surface of vertically aligned n-Si micropillar arrays using a chemical vapor deposition technique. The three-dimensional (3D) WO₃–Si nanorod forest improves photoelectrochemical performances; it exhibits higher photocurrent density and a more negative onset potential of 0.5 V vs. reversible hydrogen electrode compared with the WO₃ nanorod array on planar Si substrate. More importantly, this directly grown 3D hierarchical structure exhibits extraordinary stability for water oxidation with negligible losses of photoactivity for 24 h in a neutral pH solution. The enhanced photostability is attributed not only to the formation of O vacancies in WO₃, which is resistive to photocorrosion but also the multiple internal reflection in 3D hierarchical structure. Our work demonstrates the importance of structural innovation in improving solar water efficiency.