Vertically nanotwinned TiO2 photoanodes with enhanced charge transport for efficient solar water splitting

Abstract Nanotwinned crystals are highly desired for materials science and practical applications due to their various intriguing properties. In particular, a semiconducting photoanode with vertically aligned twin boundaries could simultaneously possess excellent charge separation and transport properties, but the synthesis remains a great challenge. Here, we report highly oriented rutile TiO2 nanotwin crystals grown on conducting substrates via a rapid hydrothermal method for the first time. The scanning synchrotron X-ray Laue nanodiffraction demonstrated that the twin boundaries in the film are strikingly perpendicular to the plane of the substrate. The nanotwin photoanode exhibited superior photoelectrochemical water oxidation activity mainly due to the massive improvement in the electrical transport. This work offers exciting opportunities for designing and fabricating new classes of ordered nanotwins.