Solar thermo-photo catalytic hydrogen production from water with non-metal carbon nitrides

Thermo-photo catalytic water splitting for hydrogen generation is a promising method for cascade utilization of full-spectrum solar energy. Herein, two g-C3N4 catalysts were synthesized using a hard-template method with different precursors (melamine for M-CN and cyanamide for C-CN) to investigate the synergistic effect between photo and thermal energies in thermo-photo catalysis. The hydrogen production rates via different pathways, including thermo-photo catalysis (TPC), thermal catalysis (TC), and photocatalysis (PC), were investigated. Results showed that the hydrogen generation rates of M-CN and C-CN catalysts via the TPC pathway at 60 °C under full-spectrum irradiation were 808.4 μmol g⁻¹ h⁻¹ and 1932.9 μmol g⁻¹ h⁻¹, respectively, which were both higher than the sum of the hydrogen production rates via TC and PC pathways, indicating the coupling effect between the photoelectric and photothermal effects of light. The thermo-photo synergy with thermal energy converted from photothermal effect is stronger than that with thermal energy from an external heat source. The mechanism of the synergistic effect was characterized by photoelectrochemical experiments, revealing that higher temperatures promote the separation and migration of charge carriers, providing a microscopic explanation for the improved hydrogen production rate of thermo-photo catalysis.