Synthesis And Electrochemical Performance Of Phenolic Resinderived Carbon And Its Composites

In this paper,a series of phenolic resin based porous carbon materials with differentdimensions and one dimensional(1D)metal/metal oxide carbon nanocomposites were prepared by sol-gel and spray drying methods using phenolic resins with excellent thermal stability as precursors.The effects of morphology control,activation mechanism and metal adsorption on phenolic resin derived carbon and its composites were studied.The intrinsic relationship between material structure and ion diffusion and electron transport mechanism in electrochemical reaction process was explored.The synergetic improvement of energy density and power density of electrical double layer capacitor(EDLC),as well as the improvement of efficient oxygen reduction ability of electrocatalyst and electrochemical property of Zn-air battery were realized.The following innovative research results were obtained:(1)The mass production of porous carbon electrode materials for high-performance EDLC has attracted much attention.Aqueous self-catalyzed polymerization and tri-component co-assembly methods combined with spray drying technology have been developed for the mass production of phenolic resin/carbon spheres.The pomegranate-like carbon microspheres assembled by spray drying can alleviate the agglomeration of the hollow carbon nanospheres with ultra-small particle size(?40nm)prepared by tri-component co-assembly method,and improve the tap-density of carbon materials at the same time.The specific surface area(1232 m² g^-1)of the carbon microspheres was further increased by steam activation,which laid a foundation for the adsorption of more electrolyte ions in the electrochemical reaction process.In addition,porous solid carbon microspheres with adjustable particle size(0.6?5.0?m)were obtained by aqueous self-catalyzed polymerization combined with steam activation.This method is mainly based on the self-catalyzed reaction between phenol derivatives and the hydrolysis products of HMTA.The yields of resin and porous carbon microspheres obtained by this method can reach 29.9 and 15.9 g L^-1,respectively.The influence factors and control mechanism of the size of monodisperse carbon microspheres were systematically studied,the mass production and environment-friendly preparation of carbon microspheres was realized.The porous carbon microspheres prepared by this two methods show excellent electrochemical performance when used as electrode materials of EDLC.The specific capacitance of the porous pomegranate-like carbon microspheres is as high as 260 F g^-1 at 1 A g^-1,while the monodisperse solid carbon microspheres have the best rate performance and show size-dependent EDLC performance:the capacitance increases with decreasing particle size.The intrinsic mechanism between the particle size and the electrochemical performance was explored,and the improvement of electrochemical property of carbon microspheres with minimum size(?600 nm)was realized.This study provides a new avenue for the mass production of monodisperse porous carbon spheres.(2)In order to further overcome the agglomeration of carbon nanospheres,we have prepared the ultrafine N-doped porous carbon nanofibers(N-CNFs)with a diameter of only?20 nm by a simple sol-gel method,achieving the transformation of nanospheres to nanofibers.This method is based on the self-assembly polymerization of phenolic resin and cetyltrimethylammonium bromide in pure water.After KOH activation,the specific surface area of the sample is 1945 m² g^-1,among which 1768m² g^-1 is contributed from the micropores.The cross-linked N-CNFs 3D networks and abundant microporosity of carbon nanofibers can effectively improve their energy storage properties.Through the systematic study of HMTA/3-aminophenol molar ratio,surfactant dosage and polymerization time,we have mastered the morphology transformation mechanism of the ultrafine RNFs.The gravimetric and area specific capacitance of activated N-CNFs are as high as 380 F g^-1 and 1.7 F cm^-2,respectively.Even under the ultra-high current density of 100 A g^-1,the specific capacitance can still reach 226 F g^-1.This is mainly due to the ultrafine diameter of N-CNFs,which greatly shortens the ion diffusion distance and accelerates the electron transmission speed.When further assembled into symmetrical EDLCs,the maximum energy density in quasi-solid-state electrolyte and organic electrolyte is 11.04 and 36 Wh kg^-1,respectively.(3)In order to solve agglomeration problem of 2D porous carbon materials and low energy density of EDLCs,we have polymerized a phenolic resin layer on the surface of graphene oxide by sol-gel method,and then embedded the small ZIF-8particles on the surface of resin.After carbonization and CO₂ activation,the carbon nanosheets with high specific surface area and 3D interconnection hierarchical pore structure were obtained.The ordered mesoporous carbon layer inhibited the agglomeration of graphene,while the ZIF-derived microporous carbon(ZDMC)particles expanded the 2D carbon nanosheet spacing.XPS study showed that the introduction of ZDMC increased the pyrrole-N and pyridine-N content,while the activation of CO₂ changed the pyridine-N part into pyrrole-N.When assembled as an aqueous supercapacitor,the specific capacitance reaches 270 F g^-1 at the current density of 0.5 A g^-1,and it has excellent rate performance and cycle stability.The specific capacitance of symmetrical EDLC based on ionic liquid is 240 F g^-1,the maximum energy density is 133 Wh kg^-1,and the power density is 9960 W kg^-1.The excellent electrochemical performance of 3D hierarchical porous carbon materials is mainly due to the widened space between 2D carbon nanosheets,which effectively reduces the ion diffusion resistance;meanwhile,the high conductivity of graphene accelerates the electronic transmission process and effectively improves the rate performance of EDLC;the construction of 3D hierarchical porous structure greatly improves the specific surface area and micropore proportion of carbon materials,which provides advantage for more ion adsorption.The design strategy of hierarchical porous carbon materials effectively alleviates the agglomeration of 2D materials and enriches the preparation science of porous carbon materials for energy storage.(4)In order to reduce the production cost and improve the catalytic efficiency of ORR electrocatalyst,we reported an efficient electrocatalyst composed of single-atom Fe N_x and?-Fe₂O₃ nanoparticle co-functionalized hollow graphitic CNFs by water activation.The activation not only introduces?-Fe₂O₃ nanoparticles,but also contributes to the transformation of hollow graphitized CNFs.HAADF-STEM,XPS,M?ssbauer spectrum and synchrotron radiation X-ray absorption spectrum(SRXAS)proved the existence of Fe N_x active center in the catalyst.In addition,?-Fe₂O₃nanoparticles as a co-catalyst could effectively boost the catalytic activity of Fe N_x.1D hollow CNF structure can improve electron transport efficiency,and the catalyst with high conductivity and specific surface area could achieve high current density and expose more Fe N_x active sites in ORR process.The half-wave and onset potential of the electrocatalyst are 0.81 and 0.95 V,respectively.The limiting current density(?6 m A cm^-2)and cycle stability(87.14%after 30000 s)are higher than the commercial Pt/C catalyst.After assembly for aqueous Zn-air battery,the open circuit voltage(OCV)reached 1.51 V,and the maximum power density and energy density are 69.42m W cm^-2 and 920 Wh kg^-1,respectively.(5)In order to further explore the advantages of 1D electrocatalyst,we designed the"adsorption-anchor"strategy to prepare 1D N-doped carbon nanorod composite with monodisperse Co quantum dots/single atoms anchored.The catalyst can effectively prevent the agglomeration of Co quantum dots/single atoms during pyrolysis and catalytic reactions.The specific surface area and nitrogen doping content of the catalyst are 478.7 m² g^-1 and 10.29 at.%.XPS,HAADF-STEM and SRXAS proved the Co N_x and Co quantum dots active centers in catalyst.As the ORR electrocatalyst,the onset potential is 0.96 V and the half-wave potential(0.84 V)is 18m V higher than that of Pt/C catalyst.The catalyst also has high limiting current density(5.69 m A cm^-2),methanol resistance and cycle stability.After assembly for aqueous Zn-air battery,the OCV reached as high as 1.54 V.The power density is76.76 m W cm^-2 at the current density of 120.50 m A cm^-2.Further assembly for solid-state Zn-air battery,the specific capacity and energy density reached 796 m Ah g^-1 and?963 Wh kg^-1,respectively.The Zn-air battery in series can drive toy cars and charge mobile phones successfully.The above researches open up a new way for the mass production and electrochemical properties of phenolic resin-derived carbon and its composites.