Magnetic CoNi@N-Doped Carbon Composite for CO₂ Electrochemical Reduction to CH₄ Associated with Methanol Oxidation to Methylal in an Ionic Liquid Electrolyte

The electrochemical reduction reaction of CO2 (CO2eRR) to high value-added chemicals in an aqueous electrolyte usually faces challenges, including sluggish oxygen evolution at the anode and the competing reaction of hydrogen evolution at the cathode. A novel CoNi@NC composite with high saturation magnetization, prepared by facile pyrolysis, was used as the cathode and a Pt sheet as the anode in an ionic liquid (IL)-methanol electrolyte to conduct the CO2eRR to produce CH4 and CO, and oxidation of methanol to generate methylal (dimethoxymethane, DMM). A magnetic CoNi alloy nanomaterial (CoNi@NC) with a nitrogen-doped carbon layer-coated structure was synthesized by a one-pot method. The system achieved an associative strategy for synchronous production of high-valued chemicals via two half-reactions at the cathode and anode, respectively. The optimal CoNi@NC composite exhibited efficient catalytic activity, obtaining an average of 54.5% faradaic efficiency (FE) for DMM within 48 h and 91.9% of momentary FE for CO and CH4 at 24 h under lower energy consumption. The electrode catalyst and ionic liquid electrolyte also exhibited good recyclability and stability in the CO2eRR. Mechanism studies indicated that magnetic CoNi alloy species served as adsorption and active sites for CO2 conversion. In addition, the carbon layer coating enhanced the stability of the CoNi alloy, and N-doping introduced surface defects on the carbon layer, thereby promoting CO2 adsorption and electrocatalytic activity. Density functional theory (DFT) calculations demonstrated that the magnetic CoNi (1 1 1) species was conducive to CO2 adsorption and activation, exhibiting high selectivity for the CO2eRR.