Direct Z-scheme WO3- nanowire-bridged TiO2 nanorod arrays for highly efficient photoelectrochemical overall water splitting

All-solid-state Z-scheme photocatalysts for overall water splitting to evolve H2 is a promising strategy for efficient conversion of solar energy. However, most of these strategies require redox mediators. Herein, a direct Z-scheme photoelectrocatalytic electrode based on a WO3-x nanowire-bridged TiO2 nanorod array heterojunction is constructed for overall water splitting, producing H2. The as-prepared WO3-x/TiO2 nanorod array heterojunction shows photoelectrochemical (PEC) overall water splitting activity evolving both H2 and O2 under UV–vis light irradiation. An optimum PEC activity was achieved over a 1.67-WO3-x/TiO2 photoelectrode yielding maximum H2 and O2 evolution rates roughly 11 times higher than that of pure TiO2 nanorods without any sacrificial agent or redox mediator. The role of oxygen vacancy in WO3-x in affecting the H2 production rate was also comprehensively studied. The superior PEC activity of the WO3-x/TiO2 electrode for overall water splitting can be ascribed to an efficient Z-scheme charge transfer pathway between the WO3-x nanowires and TiO2 nanorods, the presence of oxygen vacancies in WO3-x, and a bias potential applied on the photoelectrode, resulting in effective spatial charge separation. This study provides a novel strategy for developing highly efficient PECs for overall water splitting.