The Preparation And Application Of Fe And N Co-doped Porous Carbon Catalyst For Oxygen Reduction Reaction

The large-scale use of traditional fossil energy?coal,oil,and natural gas?has caused a series of ecological and environmental problems,it is urgently needed for people to develop clean energy with sustainable development.In recent years,fuel cells?FCs?,as a new type of renewable and environment-friendly energy devices,have played an extremely important role in energy storage and conversion,and therefore have attracted more and more attention.At present,an important issue that limits the commercial application of proton exchange membrane fuel cells?PEMFCs?is the sluggish kinetics of oxygen reduction reaction?ORR?.Currently,platinum-based catalysts?Pt/C?are widely used because of their good ORR activity.However,the Pt is expensive,limited reserved,and the methanol permeation of the proton exchange membrane would lead to the ORR performance decrease of the Pt catalyst.These factors hinder the commercial application of platinum-based catalysts in PEMFCs.Therefore,research and development of the economic and environmental friendly raw materials,low cost,high resistance to methanol,efficient and stable non-precious metal ORR catalyst instead of platinum-based noble catalyst to reduce the cost of fuel cells,is of great significance for the large-scale use of fuel cells.In this work,a series of as-synthesized non-noble metal electrocatalysts with different morphology and structure were prepared by using natural product red dates,polyacrylonitrile?PAN?,and polyaniline?PANI?as carbon sources,respectively,g-C₃N₄ as both sacrificial template and nitrogen source,and ferrous acetate as iron source.The ORR performance of the prepared catalysts was also investigated to establish the structure-activity relationship of the catalysts.The specific research contents of this paper are as follows:1.A series of three-dimensional structures iron and nitrogen co-doping carbon materials?Fe-N-C_R?were prepared by using red date as carbon source,g-C₃N₄ as both sacrificial template and nitrogen source,and ferrous acetate as iron source,through solid-phase grinding and high-temperature thermal decomposition methods.The morphology and structure of Fe-N-C_R were characterized by XRD,XPS,BET,Raman and TEM.The ORR properties of Fe-N-C_R catalyst were studied by electrochemical workstation combined with rotating disk electrode.The results show that the introduction of g-C₃N₄ can significantly increase the specific surface area of the catalyst and promote the uniform dispersion of iron nanoparticles on the carbon support material,the active species of the catalyst is closely related to the amount of Fe.With the increase of Fe dosage,the active species are gradually changed from Fe-Nx to Fe/Fe₃C.The limiting current density of optimized Fe-N-C_R sample?Fe-N-C_R-2?with rich Fe-Nx active sites can reach 4.50 mA?cm^-2 at-0.40 V,which is higher than that of commercial Pt/C(4.42 mA?cm^-2),the half-wave potential of Fe-N-C_R-2 is-0.05 V,which is close to-0.03 V for commercial Pt/C.The stability test results showed that Fe-N-C_R-2 has a current retention of 90.7%after 10000 s measurement,which was higher than 55.9%of commercial Pt/C catalyst.2.Iron and nitrogen co-doped carbon fiber series samples?Fe-N-CF?were prepared by using polyacrylonitrile as carbon source,g-C₃N₄ as both sacrificial template and nitrogen source,and ferrous acetate as iron source,through electrospinning and pyrolysis methods.By adjusting the amount of g-C₃N₄ dosage,the morphology of the Fe-N-CF series samples could be controled.The physico-chemical and electro-chemical characterization results show that with the increasing amount of g-C₃N₄,the morphology of the prepared Fe-N-CF is transfered from carbon fiber with smooth surface to 3D carbon fiber/porous carbon composite structure,and then to porous carbon structure.The Fe-N-CF_3/1-1%sample exhibits large specific surface area and hierarchical pore structure,which is not only favorable for the good dispersion of the active component but also favorable for the transmission of reactant/product molecules,and thus presents good ORR performance.The half-wave potential of Fe-N-CF_3/1-1%for ORR is-0.04 V?commercial Pt/C is-0.03 V?,the limiting current density is 4.32 mA?cm^-2(commercial Pt/C is 4.42mA?cm^-2),and current retention is 83.2%after 10000 s measurement?commercial Pt/C is 55.9%?.3.A polyaniline modified g-C₃N₄ material?PANI-g-C₃N₄?was obtained by in-situ polymerization of aniline?ANI?on the surface of g-C₃N₄.This material was mixed with ferrous acetate by solid phase grinding and then pyrolysed to obtain three-dimensional porous carbon material Fe-N-C_PANI.The effect of iron dosage on the ORR properties of the prepared samples was preliminary studied.The experimental results show that Fe-N-C_PANI-2 sample with 12.57 wt.%of Fe possess a high specific surface area(795.41 m²·g^-1),the Fe species in Fe-N-C_PANI-2 is mainly Fe₃O₄.The half-wave potential of for ORR is-0.03 V,which is comparable to that of commercial Pt/C,the limiting current density of Fe-N-C_PANI-2 is better than that of commercial Pt/C(4.32 mA?cm^-2),the stability test results showed that Fe-N-C_PANI-2has a current retention of 90.7%after 10000 s measurement,which was better than55.9%of commercial Pt/C.