Preparation Of Pitch-based Carbon Materials For Electrochemical CO₂ Reduction

The global climate change caused by the massive emission of carbon dioxide,which has led to serious environmental and social problems.Electrochemical CO₂ reduction reaction?CO₂RR?,which can directly convert CO₂ into value-added chemicals or fuels under ambient temperature and pressure,is a promising option among various CO₂ conversion methods,particularly when it is driven by the renewable energy sources.However,the slow reaction kinetics and poor product selectivity remain major bottlenecks of CO₂RR large-scale applications development.It is urgent to develop high performance electrocatalysts for CO₂RR.The carbon-based catalysts,which mainly reduce CO₂ to CO,have been widely investigated due to their low production cost,environment-friendly and good electrochemical durability,but the problems of low catalytic activity and high voltage sensitivity need to be solved.Nitrogen-rich pitch,a quinoline-polymerized soft carbon precursor,is an excellent precursor for preparing carbon-based materials due to it exhibit high nitrogen content and high conductivity.In this paper,nitrogen-rich pitch was used as precursor to control the chemical composition,microstructure,pore structure and morphology of pitch based carbon materials by organic fusion template replication and in situ co-pyrolysis.High-performance transition metal and nitrogen co-doped carbon nanosheets and ordered mesoporous carbons were successful synthesized,and the effects of multi-scale structure on the electrochemical properties of the materials were studied.The main research contents of thesis are as follows:?1?The transition metal and nitrogen co-doped pitch-based carbon nanosheets were fabricated through nitrogen-rich pitch as precursor and sodium chloride as template and introducing transition metal salts.The CO₂RR catalytic activities of pitch-based carbon nanosheets were discussed by exploring different transition metal and quality of transition metals.The results show that the nickel-nitrogen co-doped pitch-based carbon nanosheet exhibits the optimal electrochemical performance.Faraday efficiency of CO at the applied potential of-0.9 V versus reversible hydrogen electrode?vs.RHE?can reaches 91%,the CO partial current density reaches 8.87 mA cm^-2 at the condition of-1.1 V vs.RHE and the Tafel slope is 146 mV dec^-1 with faster reaction kinetics.?2?The nickel and nitrogen co-doped pitch-based ordered mesoporous carbon material was synthesized using N-rich pitch as carbon source and nitrogen source,NiCl₂·6H₂O as nickel source,mesoporous silica SBA-15 as the hard template.The effects of Ni-N active sites,pore structure and carbonization temperature were investigated.The nickel and nitrogen co-doped pitch-based ordered mesoporous carbon,which exhibits a high Faradaic efficiency of CO over90%in a wide potential range from-0.75 to-1.20 V vs.RHE.The maximum FE of CO can reach 93.3%at-0.90 V vs.RHE,and the corresponding partial current density for CO is about15 mA cm^-2.The TOF of Ni-NOMC-900 is calculated to be 1224 h^-11 at-0.9 V vs.RHE.Both current density and FE of CO did not decrease significantly during the 10 h electrolysis.Such excellent catalytic activity is mainly attributed to the engineered Ni-N active sites and unique ordered mesoporous structure,which enhances CO₂ activation,increases the CO₂ concentration of active site near to enlarge the working window of electrocatalytic reaction of carbon materials.This work provides a facile and effective strategy for the synthesis of low voltage sensitivity and high reaction selectivity electrocatalysts,providing great application potential in CO₂RR powered by renewable energy.