Facile and efficient atomic hydrogenation enabled black TiO2 with enhanced photo-electrochemical activity via a favorably low-energy-barrier pathway

Black TiO2 has demonstrated a great potential for a variety of renewable energy technologies. However, its practical application is heavily hindered due to lack of efficient hydrogenation methods and a deeper understanding of hydrogenation mechanisms. Here, a simple and straightforward hot wire annealing (HWA) method is presented to prepare black TiO2 (H-TiO2) nanorods with enhanced photo-electrochemical (PEC) activity by means of atomic hydrogen [H]. Compared to conventional molecular hydrogen approaches, the HWA shows remarkable effectiveness without any detrimental side effects on the device structure, and simultaneously the photocurrent density of H-TiO2 reaches 2.5 mA cm-² (at 1.23 V vs reversible hydrogen electrode (RHE)). Due to the controllable and reproducible [H] flux, the HWA can be developed as a standard hydrogenation method for black TiO2. Meanwhile, the relationships between the wire temperatures, structural, optical, and photo-electrochemical properties are systematically investigated to verify the improved PEC activity. Furthermore, the density functional theory (DFT) study provides a comprehensive insight not only into the highly efficient mechanism of the HWA approach but also its favorably low-energy-barrier hydrogenation pathway. The findings will have a profound impact on the broad energy applications of H-TiO2 and contribute to the fundamental understanding of its hydrogenation.