Preparation And Electrochemical Properties Of Phenolic Resin-based Carbon Spheres

With the rapid increase in the global energy consumption,new energy devices such as supercapacitors and fuel cells have ushered in a new round of development opportunities.For all energy storage and conversion devices,electrode materials are the core components.Carbon materials have attracted numerous researchers due to their diversified properties.They have become excellent candidates for electrochemical electrode materials because of their good electrical conductivity,easy-to-control structure and low price.In this paper,resorcinol-formaldehyde（RF）resin and m-aminophenol-formaldehyde（APF）resin were selected as carbon precursors,and the corresponding carbon materials were obtained by adding different surfactants or metal doping methods.The effects of different conditions during the preparation on the morphology and structure of carbon spheres were investigated,and they were used as electrode materials to evaluate their performance in supercapacitors and oxygen reduction reactions.The specific research contents are as follows:First,we synthesized resorcinol-formaldehyde（RF）resin spheres modified with surfactants.In the preparation process,we added several different surfactants as soft templates:cetyltrimethylammonium bromide（CTAB）,sodium dodecyl sulfonate（SDS）,polyvinylpyrrolidone（PVP）and poly（ethylene glycol）-block-poly（propylene glycol）-block-poly（ethylene glycol）（F127）.Different surfactants interact differently with the long chain of the phenolic resin during the polymerization process,and ultimately affect the spherical morphology of the carbon sphere.Among them,the carbon spheres formed with CTAB are uniform in size,when SDS is added,many flake structures appear in the product,and the carbon spheres obtained by adding PVP or F127 have a wide particle size distribution.Therefore,CTAB was selected for the next study,by changing the concentration of CTAB we can further explore the changes in the pore volume and specific surface area of the carbon spheres.C-0.002,which has the best specific capacitance properties,has a specific capacitance of 178.5 F g^-1 at a current density of 0.5 A g^-1,which is larger than that of carbon spheres(131 F g^-1)without CTAB.Then,we synthesized iron-doped m-aminophenol-formaldehyde(Fe³⁺/APF)resin spheres.The m-aminophenol-formaldehyde resin has nitrogen-rich groups,when Fe³⁺and surfactant F127 are added in the polymerization process and further give a high temperature pyrolysis,it can be doped with Fe and N elements to obtain Fe/N-doped porous carbon spheres（Fe/NPCSs）.During the polymerization process,the two conditions of Fe³⁺concentration and surfactant F127 were controlled to obtain several different Fe/N-doped carbon spheres.By evaluating the differences in morphology,structure,and specific surface area of each material,Fe/NPCSs-M with the best oxygen reduction（ORR）catalytic performance was selected,and the ICP resluts showed that the Fe doping amount in Fe/NPCSs-M was 0.28 wt.%.The ORR test gives that the onset and half-wave potentials of Fe/NPCSs-M are 0.92 V and 0.78 V,respectively,which are comparable to commercial 20%Pt/C catalysts（0.94 V and 0.82 V）.The RRDE test shows that the oxygen reduction reaction undergoes a 4-electron transfer process under the catalysis of Fe/NPCSs-M,which is a very useful electron transfer path for ORR,and the by-product H₂O₂yield is less than 4%.Similarly,the methanol resistance and cycle stability of Fe/NPCSs-M are also better than Pt/C catalysts.Therefore,the polymerization of the nitrogen-containing monomers in this paper eliminates the nitridation process in the conventional preparation method,and the obtained phenolic resin-based material Fe/NPCSs-M is a very promising ORR catalyst.