Preparation Of Hierarchically Porous Carbon Spheres And Carbon Films By Polymer Phase Conversion Method

Porous carbon materials have the advantages of both carbon materials and porous materials,having good electrical and thermal conductivity,strong resistance to high temperature corrosion,but also having hierarchically pore structure for electrochemical energy storage,adsorption and separation,and catalysis.In order to meet the demands of industrial applications,there are sereval requirements on the shape,pore structure,and mechanical strength of porous carbon materials.In this paper,a polymer phase conversion method has been developed to prepare spherical porous carbon and film-like porous carbon materials.The phase conversion process and microscopic structure of carbon materials were studied.The main conclusions are summarized as follows:(1)The preparation of carbon membrane.Through a solvent-induced phase separation,carbon membranes with a large number of finger-like pores were obtained by using polyacrylonitrile(PAN)as carbon precursors.Through a combination of solvent-induced and temperature-induced phase separation,carbon membranes consisting of finger-like pores and spongy structures were prepared.Through a series of conditional experiments,the optimal experimental conditions were obtained for carbon membrane as:PAN molecular weight of 85000,PAN concentration of 14wt%,the nonsolvent-bath composition of water/ethanol of 7:3 or DMF/water/ethano 1 of 3:4.9:2.1.The addition of polymer additives such as polyethylene glycol(PEG),PVP,and PMMA could adjust the structure of phase separation.It was found that the PMMA could cause the formation of macroscopic defects,while PVP and PEG could induce the homogenous macrophase separation,leading to plenty of accessible macropores onto the surface compact layer.(2)The preparation of carbon spheres.Millimeter-scaled carbon spheres were prepared by an solvent-induced phase conversion process through dropping a PAN solution droplet into non-solvent coagulation bath,which could lead to a quick phase separation to form a solid PAN bead.The optimal experimental conditions were determined for carbon spheres as:PAN molecular weight of 85000,PAN concentration of 14wt%,PVP molecular weight of 24000,PVP concentration of 3wt%and the nonsolvent-bath comosition of water/ethanol of 7:3.The as-obtained carbon beads have percolating macroporous superstructure with axial-oriented macrovoid channel and sponge-like bicontinuous network.Moreover,the addition of PVP could open the surface compact layer of carbon spheres,which greatly improve the potential of carbon spheres for applications where surface diffusion process is necessary.The resultant carbon spheres have a high mechanical strength of 23.3 N and considerable BET surface area of 523.8 m2/g.(3)Rapid oxidation of PAN spheres using a fluidized bed.PAN Oxidation is a strong exothermic reaction which could be a key obstacle in industrial production.Herein,we developed a fluidized bed system to oxidize the PAN spheres,which could greatly shorten the oxidation tirne and improve the oxidation efficiency.