Defect-Rich Gas–Solution Photocatalytic Systems for Nitrogen Reduction Reactions: Enabling Energy and Carbon Reductions

The efficient and sustainable production of ammonia is pivotal for global food security and energy sustainability. In this study, we developed a novel gas-solution (G-S) photocatalytic nitrogen reduction reaction (PNRR) system utilizing molybdenum oxide deposited onto carbon fiber paper (MoO₃@CFP) and a low-cost 24 W plant lamp as the illumination source. The G-S system eliminates the need for nitrogen gas bubbling by relying on ambient air as the nitrogen source and was demonstrated to be a simplified and scalable approach to ammonia production. The amorphous structure of MoO₃@CFP provides abundant active sites and defect centers, enabling effective nitrogen activation and reduction. Under optimized conditions (current = 0.25 A, deposition time = 600 s, stirred), the system achieved a mass-normalized ammonia production rate of 15.144 mmol·g^-1·h^-1 and sustained performance over five consecutive cycles (1 h per cycle). Material characterization confirmed the structural integrity and compositional stability of the catalyst after repeated use. A working mechanism is proposed in which Mo-O-Mo linkages and defect sites facilitate electron transfer and nitrogen activation. Overall, this study introduces a cost-effective route to photocatalytic ammonia synthesis using ambient air in a G-S configuration.