Thin-film Cu1−xNx catalysts for efficient CO2 reduction: a scalable magnetron sputtering approach

Abstract

Thin-film-based catalysts, fabricated through physical vapor deposition, have attracted significant interest as promising materials for electrochemical CO₂ reduction. In this context, metallic Cu films function as active catalyst layers for the reduction to ethylene and ethanol. However, these films still experience high overpotentials, resulting in low energy efficiencies. In this study, we have fabricated Cu_1−xN_x films to overcome this issue by incorporating nitrogen into the sputtering process, leading to the formation of an anti-ReO₃ crystal structure of Cu₃N, which contains interstitial vacancies filled with Cu atoms. Under optimal sputtering conditions of r_N2 = 0.50, sputter rate = 4 Å s⁻¹, and pressure = 6 μbar, EDX analysis reveals a sub-stoichiometric thin-film composed of Cu_0.84N_0.16. In the electrochemical CO₂ reduction, this film resulted in an increase in energy efficiency from 15.8% to 20% for ethylene compared to pure Cu films, which was attributed to a decrease in the measured potential by ± 500 mV, due to the addition of nitrogen in the structure. This key finding suggests that for future applications, Cu_1−xN_x layers should be employed instead of metallic Cu to reduce the required energy demands while maintaining selectivity.