Photothermally catalytic fixation of N2 over TiO2 loaded onto carbon paper by fast Joule heating

Combining interfacial solar evaporation with a three-phase photocatalytic system can theoretically improve the production efficiency of ammonia. Herein, we designed a simple solar evaporator via in situ growth of TiO₂ onto hydrophilic carbon paper using a fast Joule heating method. This system had porous channels for high water evaporation rates, wide light-responsive wavelength range, effective light absorption, and potentially high catalytic activity. The lattice disorder and oxygen vacancies created by the rapid heating and cooling process could be reaction sites for nitrogen adsorption and activation. The ammonia yield in the three-phase system was up to 360.37 mol·g⁻¹·h⁻¹, which was higher than the two-phase system (17.14 μmol·g⁻¹·h⁻¹). Additionally, the ammonia yield rate was 73.65 μmol·g⁻¹·h⁻¹ in an outdoor test, demonstrating the potential for large-scale solar nitrogen reduction reaction (NRR). As detected, the activation energy for N₂ reduction to NH₃ was reduced to 26.3 kJ·mol⁻¹, indicating that this process was facilitated by the design of the photothermal–photocatalytic system. Furthermore, density functional theory (DFT) calculations confirmed the roles of oxygen vacancies as active sites in promoting the NRR. This work provided a new approach to applying solar evaporators for the highly efficient ammonia production by the synergistic effects of photothermal and photocatalytic processes.

Graphical abstract