Lithiation-Enabled High-Density Nitrogen Vacancies Electrocatalyze CO 2 to C 2 Products.

Electrochemical CO ₂ reduction to produce valuable C ₂ 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 (Cu ₃ N _x ) feature as efficient electrocatalytic centers for CO-CO coupling to form the key OCCO* intermediate toward C ₂ products. Cu ₃ N _x 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 C ₂ intermediates are strongly correlated with nitrogen vacancy density. The Cu ₃ N _x catalyst with abundant nitrogen vacancies presents one of the highest Faradaic efficiencies toward C ₂ products of 81.7 ± 2.3% at -1.15 V versus reversible hydrogen electrode (without ohmic correction), corresponding to the partial current density for C ₂ production as -307 ± 9 mA cm ^-2 . An outstanding electrochemical stability is also demonstrated at high current densities, substantially exceeding CuO _x catalysts with oxygen vacancies. The work suggests an attractive approach to create stable anion vacancies as catalytic centers toward multicarbon products in electrochemical CO ₂ reduction.
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