Study On Electrocatalytic Carbon Dioxide Reduction Based On Rare Earth Single-atom Carbon-based Materials

Electrochemical CO₂ reduction reaction（CO₂RR）is considered a promising technology for carbon recovery and renewable energy storage owing to its mild reaction conditions and the ability to convert or store renewable electricity.The electrochemical conversion of CO₂ to CO involves only a two-electron transfer step,with favorable reaction kinetics and relatively high selectivity,which makes it technically more suitable for industrial applications,therefore CO has become one of the most studied reduction products in the field of CO₂RR research.Among the CO₂RR electrocatalysts developed yet,single-atom catalysts have been extensively studied due to their properties such as homogeneous active sites and ultra-high atomic utilization.Rare earth elements are exceptionally abundant in electronic energy levels,especially with unfilled 4f and 5d orbitals,the property that allows the regulation of the electron density around rare earth elements and thus also makes the synthesis of rare earth single atoms possible.If the particle size of rare earth metals can be reduced to the atomic scale and applied to the field of carbon neutrality,it is not only expected to realize the efficient utilization of rare earth resources,but also to transform CO₂ into treasure and achieve carbon balance and carbon neutrality.In this paper,two rare-earth single-atom carbon based materials were applied to electrochemical CO₂ reduction,which were prepared by cascade anchoring and organic coordination strategies The following work was carried out in this paper:Firstly,rare-earth single Pr atoms were first prepared by a cascade anchoring strategy using porous carbon as the substrate and cheap and readily available glucose and dicyandiamide as materials.The single-atom distribution of Pr elements within the substrate was confirmed by a series of characterizations,and its electrocatalytic CO₂RR performance at room temperature was investigated.The structure of the prepared rare-earth single Pr atom material was verified by first-principles calculations,as well as the possible mechanism and electronic structure of its electrocatalytic CO₂RR was investigated.The rare-earth single Pr atom material prepared under pyrolysis conditions at 800℃ exhibited the best electrocatalytic CO₂RR performance with a high Faraday efficiency of CO(FE_CO)up to 93%at a low potential of-0.43 V vs RHE.At the same time,it can maintain more than 83%Faraday efficiency after 12 hours of electrolysis,showing excellent stability.Theoretical calculations and synchrotron characterization show that Pr atoms prefer to be coordinated with six N atoms instead of the common transition metal tetra-coordination,and theoretical calculations indicate that the step of CO₂ activation to*COOH has the lowest free energy which is the possible rate-determining step for electrocatalytic CO₂RR of this material.Secondly,Ni-Y bimetallic catalysts were successfully prepared by using porous carbon as the substrate and the organic ligand strategy to adjust the local electron density of Ni elements by utilizing the rich electron orbitals of rare earth Y elements and their large size radius.The characterization by X-ray diffraction（XRD）and spherical aberration-corrected electron microscopy confirmed the single-atom distribution of rare-earth Y elements within the substrate,while Ni elements were distributed in the form of tiny nanoclusters within the substrate.The Ni-Y bimetallic catalyst material prepared under the pyrolysis conditions at 850℃ has the best electrocatalytic CO₂RR performance with a high Faraday efficiency of CO up to 89%at a potential of-0.93 V vs RHE.At the same time,it can maintain more than 80%Faraday efficiency after 12 hours of electrolysis with no apparent decrease in current density,showing excellent stability.