Tailoring Cu₃N_x clusters on TiO₂ nanosheets to the sub-nanometric scale for enhancing NH₃ photosynthesis

Ammonia (NH₃) is an essential agriculture fertilizer and a promising hydrogen carrier, making its sustainable production a priority. Photocatalytic NO₃⁻ reduction offers an efficient, light-driven pathway towards NH₃ synthesis, addressing both energy and environmental challenges. In this study, we explore Cu₃N_x cluster incorporated TiO₂ nanosheet catalysts, where sub-nanometric Cu₃N_x clusters enhance NH₃ production by increasing active site accessibility, stabilizing Cu⁺ states, and enabling efficient electron–hole separation. Consequently, the CN0.3 catalyst (Cu₃N_x size = 0.3 nm) demonstrates an NH₃ production rate 158 times higher than that of pristine TiO₂ nanosheets, with excellent stability and an apparent quantum yield of 14.2 % at 330 nm. Density functional theory calculations further reveal that Cu₃N_x stabilizes NO₃⁻ adsorption, lowers the energy barrier for the rate-determining deoxygenation step, and facilitates effective charge transfer. Our findings highlight the potential of Cu₃N_x/TiO₂ as a robust candidate for efficient photocatalytic NH₃ synthesis and underscore the potential of sub-nanometric metal-nitride clusters in photocatalysis.