Photocatalytic hydrogen production over Rh-loaded TiO2: What is the origin of hydrogen and how to achieve hydrogen production from water?

The utilization of sacrificial reagents is one of the most common strategies to accelerate hydrogen production from water via a photocatalytic process. However, herein, solid isotope labeling evidences revealed that hydrogen was mainly produced from methanol (the sacrificial molecule) instead of water in the room-temperature photocatalytic reaction over Rh-loaded TiO2. In contrast, the production of hydrogen mainly from water was achieved by introducing thermal energy into the photocatalytic process as a novel thermo-photo catalytic approach, in which the active species changed from protons to water molecules. Furthermore, while the thermal (kinetic) energy introduced by elevating the reaction temperature could increase the oxidation driving force and thus improved the photocatalytic efficiency under visible light irradiation, photo energy in turn accelerated thermal catalysis via reducing the oxidized Rh nanoparticles and enhancing the interaction between Rh and TiO2. Consequently, 1500-fold enhancement in the hydrogen production rate under visible light irradiation was achieved. These findings not only highlight the vital importance to identify the reaction pathway of hydrogen production but also should inspire more efforts into the synergetic effects of energies.