Synthesis Of Coal-based Nitrogen-doped Carbon Catalysts And Their CO₂ Electroreduction Performances

In recent years,in order to deal with the serious environmental problems caused by the rapid increase of atmospheric carbon dioxide concentration,the technology of carbon dioxide conversion has attracted more and more attention.Among many CO₂ conversion technologies,electrocatalytic reduction has become a hotspot in recent years due to its advantages of mild reaction conditions and environmental friendliness.Electrocatalysts are the core technology in the process of CO₂ electrochemical reduction.Carbon materials are considered as the most promising new electrocatalysts due to their low cost and high stability.However,it is still remains many disadvantages hindering its development,such as low selectivity and low current density.Coal as a widely existing fossil energy,is mainly used for burning power generation and heating,which is the source of environment problems and greenhouse effect in China.It is the fundamental to solve energy and environmental problems to rationally mine and refine coal to realize high added value utilization.Herein,we synthesized high selectivity N-doped porous carbon and M-N-C through ball-milling,carbonization,impregnation,activation and other technical means by using coal as the precursor.The relationship between its structure and electrocatalytic properties was revealed.The main contents are as follows:?1?The N-doped porous carbon?denoted as CNPC?was synthesized using a bituminous coal as precursor through ball-milling,acid washing and controlled ammonia etching process.The effects of temperature on nitrogen doping amount,nitrogen species,pore structure and electrochemical reduction performance were investigated.In order to explore the universality of the process method,different rank coals?lignite and anthracite?were used as precursor by the same method.When evaluated as electrocatalyst in CO₂RR,the CNPC-1100 can convert CO₂ into CO with a high FE of 92%at the low potential of-0.6 V versus reversible hydrogen electrode?vs.RHE?.CNPC-1100 shows the smallest Tafel slope(¹63 mV dec^-1),indicating a faster kinetics for CO production.The current density maintains a steady value at around 1.0 mA cm^-22 throughout the duration of the electrolysis,which was tested at-0.6 V vs.RHE for 8 h.Furthermore,the FE for CO is preserved as?80%,indicating the excellent electrochemical stability of CNPC-1100.By comparing the electrocatalytic properties of catalysts synthesized by using different rank coals,it is found that the properties of materials unchanged with the change of coal rank,which proves that the method is universal.?2?The Ni-N-C porous material was synthesized using a activated carbon which was prepared by using a bituminous coal as precursor through KOH activation,then through Ni?NO₃?₂ impregnation and carbonization with CO?NH₂?₂ in a certain proportion.The effects of Ni,N and temperature on electrochemical reduction performance were investigated.When evaluated as electrocatalyst in CO₂RR,the Ni-CNPC-650 can convert CO₂ into CO with a high FE of 93%at the low potential of-1.0 V versus reversible hydrogen electrode?vs.RHE?.The current density maintains a steady value at around 4.0 mA cm^-22 throughout the duration of the electrolysis,which was tested at-1.0 V vs.RHE for 10 h.Moreover,the FE for CO is still higher than 80%,indicating the excellent electrochemical stability and selectivity of Ni-CNPC-650.By comparing the performance with CNPC-650 and Ni-CPC-650,it is proved that the current density was improved due to the presence of Ni-N.The high pyridinic-N content and large specific surface area of the material provide abundant catalytic active sites,and the abundant pore channels are conducive to the rapid transfer of reactants and products,all the mentioned above ensure the excellent electrocatalytic performance.