A Triple-Site Engineered Heterojunction Photocatalyst for Full-Spectrum NH₃ Synthesis via Synergistic Promotion of Water Oxidation and Nitrate Reduction

Photocatalytic nitrate reduction reaction (NitRR) represents a sustainable approach to convert nitrate pollutants to valuable NH₃. However, the performance of state-of-the-art photocatalysts is hampered by insufficient near-infrared (NIR) light utilization and sluggish kinetics of hydrogenation steps and coupled water-oxygen reaction (WOR). Herein, we report a NIR-response S-scheme heterojunction photocatalyst with engineered triple-active sites for NH₃ production. The integration of narrow-bandgap CuS and Co-based metal–organic framework (Co-MOF) into an S-scheme heterojunction enhances the NIR light harvesting and charge separation. At the heterointerface, the Cu and Co sites drive WOR and NitRR, respectively. Acting as a dynamic proton relay, the bridging S sites capture protons from H₂O to facilitate its dissociation at Cu sites and sequentially transport the protons to Co sites to promote the hydrogenation steps. The synergy of Cu, S, and Co sites thereby induces an interfacial dynamic proton transfer mechanism for balancing the kinetics of the two coupled reactions. Taken together, an NH₃ production rate of 5750.06 µmol g⁻¹ h⁻¹ is achieved with an apparent quantum yield of 13.27% at 600 nm and 11.63% at 1000 nm, and a solar-to-chemical conversion efficiency of 0.11%. This work provides valuable perspectives into the design principles of advanced nitrate reduction photocatalysts.