Controllable Preparation Of Iron/Nitrogen Co-doped Porous Carbon-based Catalysts And Their Catalytic Performance For Oxygen Reduction Reaction

Fuel cells are considered to be the most promising energy power plants in the future due to their high energy conversion rate and no pollution emission.However,the slow reaction kinetics of the cathode oxygen reduction reaction（ORR）and the diversification of the reaction pathway are the key factors affecting the efficiency of the entire battery.At present,Pt-based catalyst is commonly used as a cathode catalyst in fuel cells,but the platinum reserves are limited,expensive,and prone to poisoning in the electrode reaction,which limits its large-scale application.Therefore,it is a hot research topic to find a high-efficiency,low-cost and high-stability non-precious metal cathode catalyst instead of Pt-based catalyst.In recent years,transition metal/heteroatom doped carbon materials have been found to have excellent oxygen reduction catalytic performance and high stability,which are expected to be novel ORR catalysts instead of Pt-based catalysts.In this paper,iron/nitrogen-doped porous carbon materials were prepared as catalysts for ORR by three different types of precursors.The morphology,structure,composition and electrochemical properties of the catalysts were characterized.The main research contents of the thesis are as follows:1.Iron-nitrogen co-doped porous carbon was synthesized as an ORR catalyst using iron-based ionic liquid as precursor.A porous iron/nitrogen co-doping carbon（Fe-N/C）with a honeycomb-like structure was successfully prepared by one-step pyrolysis using a silica sphere as a template,a green ionic liquid[Bmim]FeCl₄ as the precursor for iron,nitrogen and carbon.The effects of different calcination temperatures on the performance of the catalyst was investigated in detail.The results show that the specific surface area of Fe-N/C⁸0000 can reach 930 m² g^-1,and the nitrogen and iron contents are 7.11%and8.37%,respectively.It showed the optimal oxygen reduction catalytic activity under alkaline conditions,and its onset potential and half-wave potential were 0.981 and 0.831 V,respectively.Compared with Pt/C catalyst,the onset potential of Fe-N/C⁸0000 is negative shift about 3 mV,but the half-wave potential is more than Pt/C about 4 mV.The catalytic oxygen reduction reaction is close to the four-electron transfer.Fe-N/C⁸0000 exhibited higher stability and methanol tolerance in comparison with the Pt/C catalyst.The excellent ORR performance of Fe-N/C⁸0000 is attributed to the large BET surface area caused by its porous structure,and the large amount of oxygen reduction active sites by doping Fe and N atoms in the carbon material.2.The iron-nitrogen-doped porous carbon sphere was synthesized using a phenolic polymer as a precursor and used as ORR catalyst.The iron element is introduced into the carbon precursor by self-assembly process of 3-aminophenol and formaldehyde during polymerization,using SiO₂ sol as hard template.The iron/nitrogen co-doped porous carbon spheres（Fe/N-PCS）with uniform size were synthesized by calcined method..Fe/N-PCS have regular morphology and rich mesoporous structure,and the uniform elements distribution.The specific surface area of Fe/N-PCS is 643 m² g^-1,and the contents of nitrogen and iron are 8.10%and 0.86%,respectively.Under alkaline conditions,the onset potential and half-potential potential reach 0.968 V and 0.838 V,respectively.The initial potential is negatively shifted by about 24 mV compared with Pt/C（0.984 V）,but the half-wave potential is about 11 mV than Pt/C（0.827 V）.The average electron transfer number is 3.89,which is close to four electronic transfer process.In addition,Fe/N-PCS also exhibits methanol tolerance and ORR catalytic stability superior to Pt/C.The excellent oxygen reduction activity of Fe/N-PCS is attributed to the synergy between iron,nitrogen and carbon,and the exposure of active sites,which enhances theORR catalytic performance.3.The iron-nitrogen-doped porous carbon material was prepared from waste biomass soybean straw as precursor.Biomass soybean straw was mixed with melamine,ferric nitrate and magnesium oxide by ball milling.Iron/nitrogen co-doped porous carbon material（Fe-N-PC）has been prepared by.one-step pyrolysis method.Fe-N-PC has a 3D porous structure with abundant void structure and a large number of exposed oxygen reduction active sites.The specific surface area of Fe-N-PC is 521 m² g^-1,and the contents of nitrogen and iron are 6.24%and 1.79%,respectively.Under alkaline conditions,the onset potential（0.989V）and the half-wave potential（0.854 V）are more positive than that of commercial Pt/C.In moreover,Fe-N-PC has also excellent stability and methanol tolerance.The superior electrocatalytic properties of Fe-N-PC can be attributed to the formation of abundant active sites in iron-nitrogen doping in carbon materials,and its unique 3D porous structure contributes to active site exposure,which accelerating the electrolytes and O₂ transmission rate.The low-cost,wide-ranging biomass soy straw has low synthesis cost,good catalytic performance and high stability,which is contributed to large-scale development of fuel cells by reducing the cost of fuel cell cathode catalysts.