Quasi-type-II amorphous red phosphorus@TiO2 hybrid films for photoanodic applications

Abstract

Owing to its optimal energy band position, red phosphorus (RP) has been considered as a promising elemental semiconductor for achieving simultaneous light-induced water oxidation and reduction. However, the photoelectrochemical performance of RP is limited by rapid charge recombination, low-charge carrier mobility, and poor water oxidation and film-forming capabilities. In this study, we explored the material strategies to address these limitations by developing a facile process to fabricate amorphous RP@TiO2 core-shell hybrid films. We found that the amorphous RP@TiO2 hybrid films annealed at low temperatures (e.g., 200–300 °C) in nitrogen exhibited significantly enhanced anodic photocurrent as compared to pure RP and pure TiO2 films due to a combined effect of enhanced visible light absorption and efficient heterointerface charge separation. Through a systematic characterization combining electronic, optical and electrochemical measurements, we found that the high density of Ti3+/oxygen vacancy complexes in amorphous TiO2 created a defect band above the valence band of RP but below the water oxidation potential, thereby inducing a quasi-type-II band alignment in the amorphous RP@TiO2 hybrid films; such electronic structure endowed amorphous TiO2 with a “hole leaky” feature to separate and transport the photogenerated holes from RP nanoparticles to exhibit an enhanced photoanodic performance.