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

Abstract

Copper nitride nanoparticles (Cu3N NPs) are emerging as promising catalysts for the electrochemical conversion of waste CO₂ into valuable multicarbon (C2+) chemicals, with efficiencies approaching industrially relevant figures of merit. However, currently available synthetic routes to Cu3N NPs are largely unsustainable. This work introduces a solvent-free, gas-phase synthesis of Cu3N 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 Cu3N phase, while electron microscopies reveal cubic NPs with sizes tunable from 10 to 50 nm by adjusting the N2 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 Cu3N NPs. This unique combination of structural and chemical features enables remarkable electrocatalytic performance toward CO2 reduction. When operated in a flow cell at an industrially relevant current density of 150 mA cm−2, the Cu3N NPs achieve Faradaic efficiencies of 50% for ethylene and 20% for ethanol, with a total C2+ 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.