Preparation Of Sulfur And Nitrogen Doped Porous Carbon Supported Fe Mn-based Single-atom Catalysis For Electrochemical Oxygen Reduction

Proton exchange membrane fuel cells（PEMFCs）have attracted wide attention because of their high energy density,no pollutants and fuel diversification.However,the cathode oxygen reduction reaction（ORR）is limited by the slow kinetics,and the precious metal platinum must be used as the catalyst,which makes the cost high and restricts the large-scale use.Therefore,it is very important to develop platinum-free catalysts with high performance and low cost.Single atom catalysts（SACs）have the advantages of high selectivity,high stability and high component utilization,as a new type of catalyst.It shows good catalytic performance and application prospect in oxygen reduction reaction.At present,the best performance is Fe SACs.In the ORR process,Fe-Nx is the key catalytic site,such as the intraplanar and marginal Fe-Nx.However,there are a few two-electron processes in the process of oxygen reduction,and the product is H₂O₂.Fe SACs are easy to react with H₂O₂,resulting in the dissolution of Fe,resulting in reduced activity and eventual deactivation.The transition metal Mnhas low reaction activity with H₂O₂ and has good stability in oxygen reduction reaction.Transition metal Mnhas a variety of chemical states（such as+2,+3,+4）,its electronic structure can be adjusted to improve the reactivity.On the other hand,Mnhas a high content in the earth’s crust and is cheap and easy to obtain,so it has a great advantage for large-scale and widespread use.Fe and Mnco-doped bimetallic catalyst,due to its unique electronic structure and the synergistic effect between the bimetallic,ORR catalytic performance and stability have been greatly improved.Since the traditional M-N₄ coordination structure contains four coordinate N,the higher electronegativity of N is not conducive to the dissociation of intermediate products,which leads to low catalytic activity.The performance will be improved by using less electronegative elements such as S to coordinate with the central metal.The doping of S also further increased the number of defects on the carbon substrate,increased the number of edge sites and structural disorder of graphene,and the change of spin state caused by S doping may lead to the improvement of catalytic activity.The main contents of this paper are as follows:（1）A kind of S,N co-doped porous carbon supported MnSACs was prepared by silica template method.We chose silica as the hard template,thiourea as the sulfur source and nitrogen source,dopamine as the supplementary nitrogen source,and manganese chloride as the manganese source.Mn-N/S-C catalyst was prepared by one-pot direct pyrolysis and then hydrofluoric acid was used to remove the template.The characterization of the material indicates the successful doping of N,S and Mn.The catalyst has very large specific surface area and pore volume,which are 1262.4 m²g^-1and 2.7 cm³g^-1,respectively.The half-wave potential and limiting current of Mn-N/S-C are 0.87 V and 5.48 mA cm^-2,respectively,which are better than 0.86 V and 5.26 mA cm^-2 of 20 wt%Pt/C,and the stability of Mn-N/S-C is also better than that of 20 wt%Pt/C.（2）A kind of S,N co-doped porous carbon supported Fe/MnSACs was prepared by silica template method.On the basis of the first system,iron nitrate was used as the iron source for doping Fe.The characterization of the material indicates the successful doping of N,S,Fe and Mn.The catalyst has verv large specific surface area and pore volume,which are 1308.4 m²g^-1 and 3.6 cm³g^-1,respectively.The half-wave potential and limiting current of Fe Mn-N/S-C were 0.86 V and 5.74 mA cm^-2,respectively,which were more better than that of 0.86 V and 5.26 mA cm^-2 of 20 wt%Pt/C,and the stability was also better than that of 20 wt%Pt/C.