Lithiation-Enabled High-Density Nitrogen Vacancies Electrocatalyze CO2 to C2 Products.

Abstract

Electrochemical CO2 reduction to produce valuable C2 products is attractive but still suffers with relatively poor selectivity and stability at high current densities, mainly due to the low efficiency in the coupling of two *CO intermediates. Herein, it is demonstrated that high-density nitrogen vacancies formed on cubic copper nitrite (Cu3 Nx ) feature as efficient electrocatalytic centers for CO-CO coupling to form the key OCCO* intermediate toward C2 products. Cu3 Nx with different nitrogen densities are fabricated by an electrochemical lithium tuning strategy, and density functional theory calculations indicate that the adsorption energies of CO* and the energy barriers of forming key C2 intermediates are strongly correlated with nitrogen vacancy density. The Cu3 Nx catalyst with abundant nitrogen vacancies presents one of the highest Faradaic efficiencies toward C2 products of 81.7± 2.3% at -1.15V versus reversible hydrogen electrode (without ohmic correction), corresponding to the partial current density for C2 production as -307± 9 mA cm-2 . An outstanding electrochemical stability is also demonstrated at high current densities, substantially exceeding CuOx catalysts with oxygen vacancies. The work suggests an attractive approach to create stable anion vacancies as catalytic centers toward multicarbon products in electrochemical CO2 reduction.