Preparation And Performance Of Electrocatalysts For Electrochemical Reduction Of CO₂ Based On Enhancing The Surface Adsorption Of CO₂

Electrochemical reduction of CO2(ERC)can be driven by clean energy and electric power,which can transform CO2 into fuels and chemicals with high added value.Therefore,ERC can effectively alleviate the problem of energy shortage as an emerging technology of energy conversion and storage.As known,the catalyst plays a crucial role in determining the performance of ERC.Unfortunately,the low solubility of CO2 in the aqueous medium electrolyte(ca.30 mM)makes the adsorption and activation of CO2 on the catalyst difficult,thus seriously limits the activity and selectivity of ERC.Traditional methtods,such as pressurization,adding ionic liquid,or adjusting the pH,have been proposed to resolve this problem.However,theses methods have been limited by the complicated procedure or high cost of equipment.In this work,we proposed a surface adsorption-enhancing strategy to prepare catalyst of ERC.A MgO/HCS catalyst with high-performance CO2 adsorption/activation and a copper-based catalyst with high-selectivity of C2H4 have been prepared through the soft template method and by means of organic ligand functionalization method.(1)Using P123 and sodium oleate(SO)as soft templates,2,4-dihydroxybenzoic acid(DA)and formaldehyde as carbon sources,and Mg(NO3)2·6H2O as magnesium sources,magnesium oxide(MgO)anchored hollow carbon spheres(HCS)composites(MgO/HCS)were prepared by hydrothermal and carbonization processes.The prepared materials are hollow and porous,and MgO is evenly distributed on HCS,which could realize the synergistic adsorption and activation of CO2 in the electrocatalytic reaction process.In 0.5 M KHCO3 electrolyte,the MgO/HCS catalyst exhibits a high selectivity for CO production with a faradaic efficiency of 81.7%at-1.0 V vs.RHE and a partialcurrent density(PCD)of 16.7 mA cm2.The mechanism studies indicate that the high electrochemical CO2 reduction performance is attributed to the synergistic adsorption/activation of CO2 by MgO/HCS.This work provides a simple strategy to improve the performance of electrocatalytic CO2,based on an in-depth study of the synergistic effect of CO2 adsorption and activation at the active site of the catalyst.(2)Copper oxide nanowire(PEI@CuO NW)composites modified by polyethylenimine(PEI)were prepared using copper foil as copper source and PEI as-NH2 source through electrochemical oxidation-calcination-physical impregnation.PEI@CuO NW materials with different PEI contents were prepared by regulating PEI solution concentration.In the electrochemical performance test,the 1%PEI@CuO NW catalyst showed the highest FE(47%)of the product C2H4,and showed good catalytic stability(-1.2 V vs.RHE)in 0.5 M KHCO3 electrolyte.The mechanism studies reveal that PEI can substantially increase the coverage of*CO on the surface of copper catalyst,which is contributed to the selective formation of C2H4 by the dimerization of*CO.This thesis proposed an effective strategy of preparing ERC catalyst by introducing CO2 affinity element to the catalysts.The resulting surface adsorption-enhancing strategy can be used to synthesize other catalyst.