Copper Ion-Guided Self-Assembly of Polyoxometalate-Based Nanosheets for Efficient Photocatalytic Nitrogen Reduction

Abstract Photocatalytic nitrogen reduction provides a sustainable pathway for ammonia synthesis, but its efficiency in pure water is limited by rapid charge recombination, insufficient nitrogen activation, and slow proton coupled electron transfer (PCET). Herein, a copper ion-guided self-assembly strategy is used to construct vanadium-doped polyoxometalate-based two-dimensional nanosheets (PMo12-xVx-TTAB-Cu, x = 0–2). TTAB intercalation promotes the formation of a layered structure and enhances nitrogen adsorption, while copper ion bridging establishes Cu–O–Mo/V interface channels for directional charge transport. In situ Kelvin probe force microscopy and quasi in situ X-ray photoelectron spectroscopy show that photoexcited electrons preferentially migrate from Mo/V centers to Cu sites, facilitating charge separation and generating electron-rich Cu centers to activate N2. Vanadium doping further enhances electron buffering capacity and PCET kinetics, thereby promoting N2 hydrogenation. Therefore, PMo10V2-TTAB-Cu achieved an NH3 generation rate of 667.12 μmol g–1 h–1 in pure water, which is 1.7 times and 3.8 times higher than that of PMo11V-TTAB-Cu and PMo12-TTAB-Cu, respectively. In situ DRIFTS and DFT calculations revealed the lateral adsorption configuration of nitrogen and the alternating hydrogenation pathway, in which vanadium doping lowered the key hydrogenation energy barrier. This study demonstrates an efficient strategy for integrating interfacial charge regulation with electronic structure engineering toward efficient solar driven nitrogen fixation.