Reactive sputter-driven gas-phase synthesis of multiporous Cu₃N nanoparticles toward sustainable CO₂ electroreduction

Copper nitride nanoparticles (Cu 3 N NPs) are emerging as promising catalysts for the electrochemical conversion of waste CO₂ into valuable multicarbon (C 2+ ) chemicals, with efficiencies approaching industrially relevant figures of merit. However, currently available synthetic routes to Cu 3 N NPs are largely unsustainable. This work introduces a solvent-free, gas-phase synthesis of Cu 3 N NPs via reactive sputtering of Cu in N₂, thereby avoiding hazardous solvents and chemicals, high processing temperatures, and excessive waste generation, and providing a fundamentally greener alternative to conventional wet-chemical methods. X-ray diffraction analyses confirm the formation of the Cu 3 N phase, while electron microscopies reveal cubic NPs with sizes tunable from 10 to 50 nm by adjusting the N 2 pressure. Positron annihilation spectroscopy, supported by density functional theory calculations, identifies vacancy clusters containing 7–10 missing atoms as the dominant defects, while sub-nanometer voids, mesopores (1.5–5.5 nm), and larger pores are also observed. X-ray photoelectron spectroscopy indicates that nitrogen vacancies contribute to vacancy clustering and reveals partial surface oxidation of the Cu 3 N NPs. This unique combination of structural and chemical features enables remarkable electrocatalytic performance toward CO 2 reduction. When operated in a flow cell at an industrially relevant current density of 150 mA cm −2 , the Cu 3 N NPs achieve Faradaic efficiencies of 50% for ethylene and 20% for ethanol, with a total C 2+ selectivity of 78%, rivaling the best values reported to date. More broadly, this work demonstrates how solvent-free, surfactant-free materials synthesis coupled with defect and porosity engineering can accelerate the development of high-performance, earth-abundant catalysts for carbon utilization.