Regulating Localized Proton Delivery in CuCo-LDH@TiO2 Heterojunctions for Selective Photocatalytic Nitrate Hydrogenation

Abstract Photocatalytic nitrate reduction can couple nitrate removal with ammonia recovery. Successive hydrogenation steps require a local supply of proton equivalents, but making water-derived hydrogen available at nitrate-reduction sites remains difficult. Here, CuCo-LDH supported on anatase TiO2 nanosheets (CuCo-LDH@TNS) is constructed to couple nitrate reduction with water/peroxide chemistry and HCHO oxidation. The optimized nominal 3% CuCo-LDH@TNS catalyst gives 94.86 ± 0.66% nitrate conversion and nearly quantitative NH4+ selectivity. Spectroscopic and isotope measurements, together with product analysis and electronic-structure calculations, support a proposed interfacial proton-equivalent relay. HCHO consumes oxidation equivalents and forms HCOOH/formate, while water remains the primary hydrogen reservoir under the tested conditions. The heterointerface therefore couples nitrate reduction on CuCo-LDH with oxidation chemistry on TNS, maintaining a kinetically accessible supply of water-derived proton equivalents. This work demonstrates that tailoring oxidation-side chemistry can effectively regulate the local hydrogen supply, offering a general design paradigm for coordinating paired half-reactions toward selective green ammonia synthesis.