Cobalt Doping in MOF-Derived Carbon-Loaded Tin Nanomaterials for Enhanced Electrocatalytic CO2 Reduction

Among many catalysts for the electrochemical reduction of CO2, bimetallic materials have been paid more attention on enhanced catalytic activity and product selectivity. Sn is considered as an optional catalyst with excellent application potential due to its high selectivity for formate, low toxicity, low cost, and abundant reserves, which has been widely studied in recent years. However, the catalytic properties of cobalt–tin bimetallic composites have not been reported. In this study, we successfully synthesized the loaded Co/Sn bimetallic carbon matrix composite using the MOF template method and systematically studied the characteristics of the composite for the electrochemical catalytic reduction of CO2. It was found that the formate Faraday efficiency (FEFormate) of the electrode with 1% Co/Sn@C catalyst coating could reach 70% with the total current density of ∼5.6 mA cm–2 at a low applied potential of −0.98 V vs RHE (reversible hydrogen electrode). Studies have shown that Co element mainly in the form of alloy doped into the catalytic materials, with trace amounts of Co doping (≤1%) can effectively improve electrode conductivity properties, increase the electrochemical active site, significantly improve selectivity for formate, and enhance the hydrogen evolution reaction (HER), which leads to more Co element doping playing a negative role. Further, the electrode with carbon paper as the support has more stable electrocatalytic activity, compared to copper foil. Experiments confirmed that the desorption of active metals on the catalyst coating on the electrode surface was the critical factor leading to the decrease in catalytic performance. This brings essential implications for the deactivation of electrodes coated with metallic elements, therefore enhancing the binding ability between the active components and the catalytic surface, or uniformly dispersing the catalytically active sites should be an effective way to improve this kind of electrode life. In addition, the carbon paper-supported 1% Co/Sn@C gas diffusion electrode (GDE) coupled with an alkaline flow cell achieved a remarkable FEFormate of ∼76% and a substantial formate partial current density of ∼24 mA cm–2 at an applied potential of −0.98 V vs RHE. Electrocatalytic experiments in the flow cell for 30 h demonstrated the excellent catalytic stability of the 1% Co/Sn@C GDE during long-term electrochemical activities.