Unlocking Efficient Sacrificial-Agent-Free Photocatalytic Nitrogen Fixation via a Polyoxometalate/Cyanoviologen Type-II Heterojunction with Synergistic Electron Transfer

Abstract For the photocatalytic reduction of dinitrogen in aqueous media, rational design of the catalyst-reactant interface is critical for achieving efficient charge dynamics and molecular activation. Herein, we constructed a type-II heterojunction based on silicomolybdic acid (SiMo12) and cyanoviologen-based coordination polymer. This modulation leads to strong interfacial electronic coupling, facilitating spatial separation of photogenerated carriers and creating a microenvironment rich in oxygen vacancies. Under ambient conditions and without sacrificial agents, the optimized 2% SiMo12 hybrid achieves an ammonia synthesis rate of 62.8 μmol·g–1·h–1. Mechanistic studies reveal that the staggered band alignment enables efficient electron transfer from the SiMo12 to viologen ligand active centers. Coupled with density functional theory calculations, the internal electron transfer pathway within the polymer molecules is clearly identified. A dynamic balance among N2 chemisorption, interfacial charge flux, and proton supply is therefore achieved through this hybrid heterostructure strategy. Overall, this work provides a sophisticated design paradigm for photocatalytic ammonia production on polyoxometalate-based hybrids by elucidating the synergistic interplay between heterojunction engineering and defect modulation.