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 (FE_CO ≥ 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 Ni^δ+ 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.