Reactive magnetron sputtered copper nitride with controlled N-coordination number for ionic polymer free CO2 electroreduction.

Copper nitride-derived materials have been demonstrated as promising catalysts for the electrochemical reduction of CO2, yet their underlying mechanism remains unclear due to the non-standardized polymer utilization in electrode fabrication. In this study, the reactive magnetron sputtering method was employed to directly deposit copper nitride on the gas diffusion layer with controlled CuN coordination numbers. Without any ionic polymer, this copper nitride electrode gave a high Faradaic efficiency of 80.84% towards C2+ products at -0.68 V vs. RHE with a partial current density reaching 240 mA/cm2 when the CuN coordination number is 2.48. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy combined with density functional theory calculations proved both the CO protonation (*CO → *COH) and the CC coupling (*CO + *COH → *OCCOH) were considered as the rate-determining steps for C2+ products, but their respective activation energies did not follow the same rule with the coordination numbers of CuN. Experiments and theoretical calculations consistently suggest that the coordination number of N must be precisely controlled to an appropriate value to balance the energy barriers of these two steps, thereby minimizing the overall energy required to convert CO2 into C2+. This work provides new theoretical guidance for designing the next generation of high-performance copper-based catalysts.