Preparation Of MOF Based Fe-N-S Co-doped Porous Carbon And Study Of ORR Activity

A proton exchange membrane fuel cell(PEMFC)is a regenerable power plant that can operate efficiently as long as uninterrupted fuel is available,as high efficiency and cleanliness stands out in many new energy sources.In PEMFC,the rate of oxidation of anode H2 is several orders of magnitude higher than that of O2 reduction of cathode.The reduction mechanism of O2 is cumbersome,and the demand for noble metal Pt is more than 8 times that of anode.At present,the precious metal Pt is the most efficient oxygen reduction catalyst,but its large-scale use has the problems of high price,low content,poor stability and easy cross-toxicity reaction with methanol.In order to realize the large-scale utilization of PEMFC,people have turned their attention to materials that are popular on the earth and that are inexpensive,to minimize the use of precious metals.Metal-organic framework material(MOF)is a new kind of porous framework carbon material.Its structure has advantages of large surface area,adjustable pore size distribution,diversity of composition,rich carbon source,etc.,and can be used as a sacrificial precursor to construct a novel M-N-C hybrid material for use in cathode reactions.This paper mainly focuses on carbon-based non-precious metal materials.For the first time,a repeating grid metal-organic framework compound IRMOF-3 is used as a precursor and iron acetylacetonate is used as an iron source.Fe/IRMOF-3 is first synthesized by a one-step ethanol solvothermal method.Then,through the second step methanol solvothermal synthesis of Fe/IRMOF-3/DMSO,the Fe-N-C-S hybrid material was synthesized by pyrolysis under nitrogen atmosphere.By optimizing the calcination temperature and the amount of sulfur introduced,a cubic porous carbon material was constructed.Fe-N-C-S(11)-900 achieves improved catalyst activity and mechanical stability.The specific work of this article is mainly as follows:1)The catalyst Fe-N-C-S(11)900 was successfully prepared by optimizing the calcination temperature and the doping amount of sulfur through a simple solvothermal-calcination method.XRD showed that the Fe-N-C-S(11)-900 doped with sulfur atoms had characteristic peaks of Fe in the crystal structure compared with Fe-N-C-900 undoped with sulfur,which improved the conductivity of the catalyst.SEM,TEM proved that Fe-N-C-S(11)-900 forms a more regular cube structure.2)XPS indicates that the presence of pyridine nitrogen,graphite nitrogen,and thiophene-C-S-C-structures in Fe-N-C-S(11)-900 facilitates the oxygen reduction reaction and confirms the successful doping of sulfur.3)Under alkaline conditions,electrochemical analysis shows:?CV curve shows that the oxygen reduction peak potential of Fe-N-C-S(11)-900 is 0.91 V,which is far from the 0.79 V of Fe-N-C-900 and is equivalent to 20%Pt/C;? The LSV test shows that the onset potential and half-wave potential of Fe-N-C-S(11)-900 is 1.042 V and 0.88 V,which is more positive than 0.84 V and 0.69 V of Fe-N-C-900,which is close to 1.043 V and 0.90 V of 20%Pt/C,which means sulfur doping increases oxygen ORR activity;? Koutecky-Levich(K-L)equations show that the number of electron transfer of Fe-N-C-S(11)-900 is 3.96,which is close to the 4-electron reaction pathway,while the number of electron transfer of Fe-N-C-900 is only 2.78.The ORR reaction process,S plays a urging role;? The chronoamperometric curve shows that after the reaction of 10000 s,the current retention of Fe-N-C-S(11)-900 is as high as 81%,while that of commercially available Pt/C is only 64%;after injecting 3 mol/L of methanol,Fe-N-C-S(11)-900 did not show significant current fluctuations,whereas the commercially available 20%Pt/C was significantly attenuated,demonstrating that Fe-N-C-S(11)-900 has better anti-fade and methanol cross-reaction ability than commercially available Pt/C;? Raman spectroscopy shows that the sulfur-doped Fe-N-C-S(11)-900 has a highly disordered carbon structure with a large number of defects,compared to non-sulfur-doped Fe-N-C-900,while Fe-N-C-900 has an order graphite carbon.Doping sulfur changes the structure of the catalyst and improves ORR performance.