Synthesis And Electrochemical Performance Research Of Ordered Mesoporous Carbon Composite Catalyst

Oxygen reduction reaction?ORR?plays an important role in energy conversion technologies such as fuel cells.However,the slow kinetics of the ORR due to its high energy barrier limits its practical application.The development of efficient ORR catalysts has a key role in promoting the development of energy conversion technologies.Iron-nitrogen-doped carbon materials?Fe/N/C?have electrochemical activity similar to commercial Pt/C in alkaline media.In addition,Fe/N/C has the advantages of low cost and simple preparation,and has become a material that can replace precious metal catalysts.The co-doping of Fe and N can effectively improve the adsorption and desorption of oxygen,and thus increase the ORR activity.The use of ordered mesoporous carbon as a support can give Fe/N/C a larger specific surface area,more molecular/ion transmission channels,and can better regulate the distribution of active sites.The reason why heteroatom doping improves the activity of ORR is that it can promote the rearrangement of charge,promote the generation of higher density active sites and the synergy between multiple atoms.Studies have found that modifying two or more non-metallic carbons can produce better ORR activity.Compared with N atom,S has a larger atomic radius and lower electronegativity,and confirms the fact that it enhances ORR activity.Based on the above problems and thoughts,we have further developed Fe/N/C materials.First,an ordered mesoporous carbon CMK-5 having a large surface area and a pore volume was used as a carrier,and 1,10 phenanthroline was used as a small molecule complexing agent and a carbon nitrogen source.The Fe/N@CMK-5catalyst with better ORR performance than the commercially available Pt/C was obtained after adding iron source and undergoing pyrolysis without acid etching.The materials have undergone comprehensive analysis of electron microscopy?SEM,TEM?,specific surface area analysis?BET?,X-ray diffraction spectroscopy?XRD?,X-ray photoelectron spectroscopy?XPS?,and electrochemical performance.It turns out that CMK-5 plays a huge role in the dispersion of active sites and gives the material a larger specific surface area.The use of zinc chloride will create more pores in the material and will limit the aggregation of active sites with complexing agent instruments,In addition,it has been found that the proper amount of iron doping has a decisive influence on the properties of the material.Fe/N@CMK-5 can generate a half-wave potential of 0.88 V and a limit diffusion current density of 5.8m A cm^-2 in an alkaline medium,and has excellent stability and methanol resistance.During the ORR process,it undergoes a four-electron reaction process.Using CMK-5 directly as a template will cause active sites to be present in both its internal and external channels.In order to locate the active material more accurately,we use CMK-5/SBA-15 as a template to load the material.The catalyst Fe NS/CMK-5 with active substance confined in the inner pores of CMK-5 was obtained through the process of pyrolytic etching after adding small molecule complexing agent bipyridine,supporting iron and sulfur.After characterization,a preparation method of active site distribution was designed to make the surface area of Fe NS/CMK-5 reach 1791 m² g^-1,which is much higher than Fe/N@CMK-5.The synergistic effect of Fe,N,S makes Fe NS/CMK-5 have electrochemical activity equivalent to Pt/C,with a half-wave potential of 0.85 V and a limiting current density of 5.8 m A cm^-2,showing a 4-electron reaction path.Through the stability tests of different methods,it was found that Fe NS/CMK-5 has good stability.In addition,it also has good methanol resistance and satisfactory hydrogen peroxide yield.