High Faradaic efficiency and appreciable current density are essential for future applications of the electrochemical CO₂ reduction reaction (CO₂RR). However, these goals are difficult to achieve simultaneously due to the severe side reaction – the hydrogen evolution reaction (HER). Herein, we successfully synthesized coordinatively unsaturated nickel–nitrogen (Ni–N) sites doped within porous carbon with a nickel loading as high as 5.44 wt% by pyrolysis of Zn/Ni bimetallic zeolitic imidazolate framework-8. Over the Ni–N composite catalysts, the CO current density increases with the overpotential and reaches 71.5 ± 2.9 mA cm⁻² at −1.03 V (vs. a reversible hydrogen electrode, RHE), while maintaining a high CO Faradaic efficiency of 92.0–98.0% over a wide potential range of −0.53 to −1.03 V (vs. the RHE). Density functional theory calculations suggest that the CO₂RR occurs more easily than the HER over the coordinatively unsaturated Ni–N site. Therefore, highly doped and coordinatively unsaturated Ni–N sites achieve high current density and Faradaic efficiency of the CO₂RR simultaneously, breaking current limits in metal–nitrogen composite catalysts.

中文翻译：

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选择性和高速率CO ₂电还原的配位不饱和镍-氮位点†

高法拉第效率和可观的电流密度对于电化学CO ₂还原反应（CO ₂ RR）的未来应用至关重要。但是，由于严重的副反应–析氢反应（HER），很难同时实现这些目标。在这里，我们成功地通过热解Zn / Ni双金属沸石咪唑酸盐骨架8，成功地合成了多孔碳中掺杂的配位不饱和镍-氮（Ni-N）位点，其镍载量高达5.44 wt％。在Ni–N复合催化剂上，CO电流密度随着过电势的增加而增加，在-1.03 V时达到71.5±2.9 mA cm ^-2（相对于可逆氢电极（RHE），同时在-0.53至-1.03 V的较宽电位范围内（相对于RHE）保持92.0–98.0％的高CO法拉第效率。密度泛函理论计算表明，在配位不饱和Ni-N位点上，CO ₂ RR比HER更容易发生。因此，高掺杂和配位不饱和的Ni-N位置同时实现了高电流密度和CO ₂ RR的法拉第效率，从而打破了金属-氮复合催化剂的电流极限。