High-performance Non-noble Metal Carbon-based Materials Applied In The Carbon Dioxide Electrochemical Reduction With A Flow Cell

The electroreduction of carbon dioxide（CO₂）into chemicals and fuels can not only reduce the greenhouse effect,but also realize the sustainable recycling of CO₂,which can effectively alleviate the problem of energy shortage.In this process,by transferring multiple protons and electrons,electrochemical CO₂ reduction reaction（CO₂RR）can obtain a variety of different gas and liquid products,such as CO,CH₃OH,HCOOH,CH₄,CH₃CH₂OH and C₂H₄.Among them,the reduction of CO₂ to CO requires only two electrons and two proton transfers,which provides a more direct and sustainable regeneration method for the synthesis of CO.However,as a key factor affecting the electroreduction of CO₂ to CO,it is crucial to explore low-cost,highly active and stable electrocatalytic materials.Among many catalysts,carbon-based materials are considered to be one of the most promising candidates for CO₂RR due to their abundant natural resources,excellent catalytic activity and long-term stability.Among them,Se-based multi-doped carbon materials and Mxene-based carbon materials have excellent catalytic performance and good selectivity in CO₂RR,and their rich resources and economy make them have great development potential.Therefore,in recent years,they have become the most expected alternative materials for precious metal electrocatalysts.In this paper,Se coupled P,N tri-doped porous carbon materials were prepared by ball milling pyrolysis method,but its catalytic performance still has some room for improvement.Therefore,it is further attempted to introduce B and Se,P,N carbon coupling to prepare fourfold-doped carbon materials to enhance their catalytic activity,thereby further improving their catalytic performance.Subsequently,two-dimensional（2D）transition metal carbide Mxene has been widely concerned because of its excellent properties.It belongs to carbon-based materials,so molecular catalysts are introduced to construct an electrocatalytic system.Studies have shown that the three carbon-based materials electrocatalysts prepared in this paper have achieved good results in catalyzing CO₂RR.The specific research contents are as follows:Part I Preparation of carbon-based SePNC electrocatalyst and its application in CO2RRIn this part,SePNC tri-doped nano-layered electrocatalysts were prepared by ball milling pyrolysis using selenium powder as Se source,triphenylphosphine as P source,ammonium chloride as N source and pore-forming agent,and sucrose as C source.The electrocatalytic performance of SePNC tri-doped nano-layered electrocatalysts in the conversion of CO₂ to CO was studied.The results of electrochemical tests by flow cell and gas chromatography show that SePNC prepared at 1050°C has the best electrocatalytic performance:the Faraday efficiency of CO(FE_CO)and the Faraday efficiency of H₂(FE_H2)are up to 94.8%and 5.2%at-0.6 V,respectively.At the same time,the electrocatalytic stability test for 12 h at-0.6 V shows that the current density of SePNC-1050 decrease slowly and remains at about 80%of the initial value,and FE_CO remains at 95.86%of the initial value,indicating that it has good stability.Part II Preparation of carbon-based Se BPNC electrocatalyst and its applications in CO2RRB has similar atomic size with C and N,but has opposite electronic properties with N,so the electronic structure of carbon can be easily adjusted.The properties between different atoms can bring many unexpected synergistic advantages to CO₂RR.In this part,a low-cost Se,B,P,N metal-free fourfold-doped electrocatalyst was prepared by replacing triphenylphosphine with tetraphenylboron tetraphenylphosphine as both B source and P source.The optimum temperature was determined to be 1050°C by screening its temperature.The best Se-BP-N-C（1050）has a FE_CO of 96.2%at-0.5 V,and the corresponding FE_H2 is only 3.8%.At the same time,the current density and FE does not decrease significantly in the10 h stability test,showing good stability.In addition,its physical characterization shows that the prepared Se-BP-N-C（1050）has a rich porous structure and a specific surface area of1023.6 m² g^-1.Part III Preparation of carbon-based Mxene/FePc electrocatalysts and their application in CO2RRMxene,a metal carbide with 2D layered structure,has attracted much attention in the field of catalysis because of its good structure and properties,high electrical conductivity,good chemical stability and multi-catalytic activity.Therefore,in this part,different proportions of Mxene/FePc electrocatalysts were prepared by first preparing Ti₃C₂T_x MXene precursor and then doping FePc with abundant Fe-N₄ active centers and low reaction energy barriers.The Mxene/FePc（1:3）sample with a ratio of 1:3 has the best selectivity for CO,and its FE_CO reaches 98.23%at-0.6 V.It has a good inhibitory effect on the hydrogen evolution reaction,and the corresponding FE_H2 is only 1.77%.At the same time,the stability test at-0.6 V for up to 24 h shows that the current density does not decrease significantly,and the FE_CO remains above 96.31%,indicating that the prepared Mxene/FePc（1:3）has good long-term stability.