Ni single atom catalyst with high Ni–Nx content for efficient electrocatalytic reduction of CO2†

Abstract

The CO₂ electrocatalytic reduction reaction (CO₂RR) is currently an effective strategy for mitigating excessive global carbon dioxide emissions and accelerating the carbon cycle. Nonetheless, there are still significant obstacles to develop CO₂RR catalysts with superior activity and excellent selectivity. Herein, we report a porous nitrogen-doped carbon material (Ni/NC-x) with high content of Ni–N_x units prepared by hydrothermal and pyrolytic methods. The content of Ni–N_x in Ni/NC-x samples was controlled by finely adjusting the proportion of additive PVP. The optimized Ni/NC-2 : 1 catalyst showed a CO partial current density (j_CO) of 46.88 mA cm⁻² and a CO faradaic efficiency (FE_CO) of up to 96% at −0.73 V vs. RHE; a FE_CO of 88% can be maintained in the flow cell while achieving j_CO of 273.63 mA cm⁻². Analysis through a thermodynamic–kinetic mechanism model suggests that the bifunctional Ni–N_x sites help to reduce the barrier of CO₂ chemisorption and provide sufficient *CO₂ for electron transfer during the reaction, hence enhancing the kinetics of CO₂RR processes.