Partially Nitrided Ni Nanoclusters Achieve Energy‐Efficient Electrocatalytic CO2 Reduction to CO at Ultralow Overpotential

Electrocatalytic CO2 reduction reaction (CO2 RR) offers a promising strategy to lower CO2 emission while producing value-added chemicals. A great challenge facing CO2 RR is how to improve energy efficiency by reducing overpotentials. Herein, partially nitrided Ni nanoclusters (NiNx ) immobilized on N-doped carbon nanotubes (NCNT) for CO2 RR are reported, which achieves the lowest onset overpotential of 16 mV for CO2 -to-CO and the highest cathode energy efficiency of 86.9% with CO Faraday efficiency >99.0% to date. Interestingly, NiNx /NCNT affords a CO generation rate of 43.0 mol g-1 h-1 at a low potential of -0.572 V (vs RHE). DFT calculations reveal that the NiNx nanoclusters favor *COOH formation with lower Gibbs free energy than isolated Ni single-atom, hence lowering CO2 RR overpotential. As NiNx /NCNT is applied to a membrane electrode assembly system coupled with oxygen evolution reaction, a cell voltage of only 2.13 V is required to reach 100 mA cm-2 , with total energy efficiency of 62.2%.