Modulating the Active Sites of Carbon-Supported Ni-Based Catalysts by Introduction of Alkaline Earth Metals for Electrochemical CO₂ Reduction to CO

The electrocatalytic reduction of CO2 to CO (eCO2RR) offers a sustainable pathway for closing the carbon cycle. However, the path of the eCO2RR remains challenging due to limitations in catalyst selectivity, activity and cost-effectiveness. Herein, a series of Ni/alkaline earth metals dispersed on N-doped porous carbon catalysts (denoted as Ni/AEMs-NC, with AEMs = Mg, Ca, Sr and Ba) were constructed by a bimetallic-site precursor pyrolysis strategy, which provided critical sites for eCO2RR. Ni/Mg-NC, Ni/Ca-NC and Ni/Sr-NC demonstrate excellent CO selectivity compared with Ni-NC. Moreover, Ni/Mg-NC exhibits superior stability and high selectivity (FECO ≥ 90%) within 50 to 200 mA cm–2, suggesting its great potential for industrial applications. Experimental and theoretical calculations reveal that AEMs alter the pyrolysis characteristics to regulate the active surface of Ni/AEMs-NC, to expose more active sites and promote electron transfer; meanwhile, they also reduce the valence state of Niδ+ and lower the energy barrier of *COOH intermediates. However, Ba tends to form additional BaCO3, which provides active interfaces for *H adsorption, kinetically favoring hydrogen evolution reaction activity. This work systematically investigates the effects of alkaline earth metals on M-NC, providing new insights and approaches for the construction of highly efficient carbon-based eCO2RR catalysts.