Coupling photothermal water evaporation and water vapor photocatalysis for efficient solar hydrogen generation

The full-spectrum solar light could be hardly utilized by semiconductor photocatalysts for solar hydrogen generation, due to the thermodynamic tradeoff between the narrow band gap required for broad solar absorption and the wide band gap for high water redox driving forces. Herein, a hybrid system coupling of photothermal water evaporation and water vapor photocatalysis, driven by carbonized wood (CW) and Pt-loaded TiO₂ (PT), respectively, has been designed for efficient and simultaneous solar hydrogen generation and water evaporation. In this CW/PT system, CW could absorb visible and near-infrared light to efficiently generate water vapor via the photothermal-evaporation processes; and then PT dispersed on the top-surface of CW would photocatalytically decompose the solar-steaming generated water vapor for hydrogen generation under ultraviolet light irradiation. In comparison to the hybrid system composed of original Wood (W) and PT (W/PT), the CW/PT system exhibits a remarkable increase in the photocatalytic performance for solar hydrogen conversion, with hydrogen generation rate reaching as high as 11.12 mmol·m⁻²·h⁻¹. COMSOL simulation results demonstrate that CW has better photothermal conversion performance than W, while its low thermal conductivity reduces heat loss, resulting the enhancement in water evaporation and hydrogen generation performances. This study provides a new idea for the full-spectrum utilization of solar energy by coupling photothermal and photocatalytic conversion processes into one system to photocatalytically decompose solar-steaming generated water vapor for efficient solar hydrogen generation.