Synthesis Of Fe-N-C Materials From Petroleum Asphalt And Their Electrocatalytic Oxygen Reduction Performance

With the increasing global energy demand and the continuous consumption of fossil energy,proton exchange membrane fuel cells have become an important alternative energy source for fossil fuels due to their many advantages such as high energy conversion efficiency,no pollution,and the wide range of fuel sources.As the most efficient fuel cell cathode oxygen reduction(ORR)catalyst,precious metal platinum-based materials have practical problems such as high cost and poor durability,which seriously restrict the development of fuel cells.Therefore,the development of transition metal-nitrogen-carbon(M-N-C,M=Fe,Co,Ni,etc.)materials with abundant resource reserves,high catalytic activity and stability has become an important breakthrough for the realization of large-scale fuel cell applications.Petroleum asphalt is a by-product in the petroleum refining process,it contains a large amount of polycyclic aromatic hydrocarbons and is a high-quality raw material for preparing carbon materials.Therefore,using petroleum asphalt as a carbon source to prepare high-performance M-N-C catalysts and applying it to proton exchange membrane fuel cells can not only achieve low-cost production of M-N-C materials,but can also provide an effective way for the high value-added utilization of petroleum asphalt.In this paper,petroleum asphalt is used as a carbon source.By designing and synthesizing active sites for electrocatalytic oxygen reduction,petroleum asphalt-based Fe-N-C electrocatalytic ORR catalysts with different structural characteristics are prepared.The structure,composition and catalytic performance of the catalysts were systematically analyzed and the structure-effect relationship was established.The specific research contents and conclusions are as follows:Firstly,Fe-N-doped carbon material was prepared by template method using nano metal oxide as template and 1,10-phenanthroline iron as precursor.The effects of heat treatment temperature,template type and other factors on the morphology and structure of the catalyst and the catalytic performance of ORR were studied.The experiment proves that the nano-Mg O template has a strong interaction with the precursor,which can effectively inhibit the migration and agglomeration of metals during the pyrolysis process.Fe-N-C/Mg O-800obtained by calcination at 800°C has the best structure and catalytic performance.Its half-wave potential is 0.91 V(vs.RHE),which is 60 m V higher than that of commercial precious metal Pt/C catalyst.And its durability and resistance to methanol interference are also better than Pt/C catalyst.Secondly,the high-viscosity petroleum pitch was used to coat the metal precursor/template to further inhibit the migration and agglomeration of the metal,the petroleum asphalt-based Fe-N-C single-atom catalysts were synthesized.The effects of the amount of petroleum asphalt,template types and precursor types on the morphology,structure and ORR catalytic performance of the catalyst were studied.The experiment proves that Fe-N-C@Asphalt-1:4 has the best catalytic performance,its half-wave potential(0.89 V vs.RHE)is better than the commercial Pt/C catalyst,and it has better long-cycle stability.The poisoning experiment proves the active centers are single atom dispersed Fe-N_x structures.The introduction of petroleum pitch not only increased the catalyst mass yield by 120%,but also increased the graphitization degree of the carbon material,conductivity and catalytic efficiency.In addition,the method has good universality and is suitable for a variety of templates and precursors.Finally,a petroleum asphalt-based porous carbon was used to adsorb ferric thiocyanate and carbonized twice to prepare petroleum asphalt-based Fe-N/S-C catalyst.Its ORR catalytic performance is comparable to commercial Pt/C,and its stability and resistance to methanol interference are better than Pt/C.It is verified that the introduction of the S element makes the carbon material have a larger specific surface area and richer defects,increases the Fe content in the carbon skeleton,provides more highly dispersed active sites,and enables the material to have an efficient catalysis closer to four electrons reaction pathway.