Preparation Of Metal/Nitrogen-doped Carbon-based Electrocatalytic Materials And Their Application In Electroreduction Of Carbon Dioxide

Converting CO₂ into valuable chemicals or low-carbon fuels through electrocatalysis can not only solve the increasingly serious energy problems,but also effectively mitigate a series of negative effects caused by the greenhouse effect.Therefore,it is of great significance for the development of renewable energy technologies and improvement of the earth’s carbon cycle.However,achieving a highly efficient electrocatalytic CO₂ reduction reaction（CO₂RR）process mainly depends on obtaining excellent electrocatalytic materials.In recent years,carbon-based materials have the advantages of low cost,excellent electrical conductivity,high specific surface area,and adjustable porosity,which they have hence become very popular electrocatalytic materials for CO₂RR process.Researchers have discovered and confirmed that the introduction of nitrogen,transition metals,etc.in traditional carbon-based materials can obtain materials with high electrocatalytic activity.Therefore,it is of far-reaching significance to further design and find transition metal/nitrogen-doped carbon materials with cheap raw materials,simple preparation process,high faraday efficiency,and stable catalytic activity for carbon dioxide electroreduction applications.The thesis aims to prepare carbon-based electrocatalytic materials for CO₂RR with low cost,high faradaic efficiency and good stability.Nitrogen-doped carbon materials were prepared by high-temperature calcination process using urea-formaldehyde resin and pentaerythritol as raw materials;On the basis of the preparation of this material,Sn-N-C and Fe-N-C non-noble carbon-based catalysts were prepared by successively introducing transition metals Sn and Fe into the nitrogen-doped carbon material.The three materials prepared in this paper are used for CO₂RR respectively,and all have produced good results for CO2 to produce adjustable synga（hydrogen and carbon monoxide）.The specific research contents are as follows:Part Ⅰ Preparation of nitrogen-doped carbon materials and its application in electroreduction of carbon dioxideIn this part,the selected melamine and formaldehyde as the main raw materials,forms urea-formaldehyde resin through polymerization under alkaline conditions.This was then combined with an appropriate amount of pentaerythritol to obtain a high-performance metal-free nitrogen-doped carbon material catalyst through a high-temperature calcination process and applied for CO₂RR.The electrocatalysis results show that the nitrogen-doped carbon catalyst has satisfactory selectivity,good current density and excellent stability for reducing products.At a potential of-0.6 V,the carbon dioxide electroreduction product FE_COO can reach 74%while FE_H2 reached 18%.It is worth mentioning that in the process of electroreduction,if the reduction potential is adjusted,the ratio of electroreduction products H₂ and CO can be controlled and adjusted as needed,with an adjustment range of 0.24 to5.25.PartⅡ:Preparation of carbon-based Sn-N-C non-noble catalyst and its application in electroreduction of carbon dioxideIn this part,melamine and formaldehyde are used to synthesize urea-formaldehyde resin,and then the resin precursor was doped with Sn salt and carbon source pentaerythritol through a high temperature calcination process to obtain a non-noble carbon-based Sn-N-C catalyst.The CO₂RR was carried out under 0.1 M KHCO₃ saturated with CO₂.The electrocatalysis study found that the Sn-N-C catalyst prepared under the conditions of heat treatment temperature of 1000°C and Sn content of 5%was the best.It has better selectivity for CO and H₂ at a potential of-0.6 V(FE_CO=63%,FE_H2=37%).The use of the Sn-N-C catalyst to control the potential can realize the composition of the generated syngas.The adjustable range is H₂/CO ratio of 8.15 to 0.60,and the catalyst shows good long-term stability in CO₂RR.PartⅢ:Preparation of non-noble carbon-based Fe-N-C catalysts and its application in electroreduction of carbon dioxideBased on the previous work,this part directly introduces the highly active transition metal Fe doped into the nitrogen-doped carbon material,and designs a high-performance non-noble carbon-based Fe-N-C catalyst.Among the prepared series of catalysts,the Fe-N-C catalyst prepared with the carbonization temperature of 950°C and the Fe content of 3%is the best.It has the best catalytic activity,good current density and satisfactory stability in CO₂RR.At-0.6 V,FE_CO is 74%,and FE_H2 is 25%.By adjusting the reduction potential,the composition of the electroreduction product syngas can be adjusted from 4:1 to 1:3（H₂/CO）,and no other liquid products are generated in the entire process.