Organic Amine-mediated Synthesis Of Carbon Microspheres For Energy-related Applications

Porous carbon materials have recently aroused great interest due to their well-developed porous structure, good electronic conductivity and excellent thermal and chemical stability, which were extensively applied in the fields of adsorption and separation, catalysts, and electrochemistry. Porous carbon microsphere is one of the most popular materials because of the controllable size and neat spherical morphology. Although there exist considerable empirical experience regarding the synthesis of RF polymer microspheres and resultant carbon microspheres, fundamental understanding of their nanostructure evolution is lacking, and therefore, the ability to rationally tailor their structure for specific applications has been limited. Thus, a general organic-amine mediated synthesis of polymer microspheres is developed based on the copolymerization of resorcinol, formaldehyde and various organic amines at room temperature. Structure formation and evolution of colloidal microsphere in the presence of polyethylenimine are monitored by dynamic light scattering measurements. The resulting nitrogen-rich carbon microspheres were obtained by a direct pyrolysis process. The CO2 adsortion and electrochemical performances of as-synthesized carbon microspheres were evulated. The major conculsions are summaried as follows:(1) Numerous nitrogen-doped polymer microspheres could be successfully prepared by a direct polymerization of resorcinol and formaldehyde in the presence of various organic amines, regarding of their molecular structures (linear, branched, ring-shaped, and ultrahigh molecular weight). The surface areas of the carbon spheres can reach 400-600 m2/g after pyrolyzed at 600? and these carbon materials show a good CO2 adsorption capacity up to 3.6 mmol·g-1 at 0? and good cycle performance. The optimum condition were as follows: the concentration was 3 wt.%, reaction temperature was 30?, PEI/R was 1.5 and carbonization temperature was 600?.(2) We further addressed the molecular weight effects of branched polyethylenimine (PEI) on the morphology and size of polymer microspheres using Dynamic Light Scattering, to monitor formation of primary clusters and subsequent structure development. An increase in the PEI molecular weight causes a gradual decrease in the average particle size and core-shell heterogeneous structures were formed. Besides, the result of DLS showed that the colloidal clusters are formed instantaneously and then experience an anomalous shrinkage-growth process. This should be caused by two different reaction pathways: cross-linking inside the microspheres and step-growth polymerization of substituted resorcinol on the microsphere surface. On the basis of the above results, a possible mechanism by which the PEI-mediated microsphere formation is proposed,and further confirmed by the characterizations such as TEM?XPS?EA and so on.(3) KOH activation is further employed to develop the porous texture of carbon microspheres without sacrificing the spherical morphology. The resultant activated carbon microspheres exhibit small particle size (< 80 nm), high BET surface areas of 1500-2000 m2·g-1 and considerable nitrogen content of 2.2-2.0 wt.%. The CO2 adsorption performance of these activated spheres has been improved greatly, which can be 6.0 mmol·g-1 at 0?. When used as the electrode materials for supercapacitor, these activated carbon microspheres demonstrate a high capacitance up to 240 Fg-1, an unprecedented rate performance and good cycling performance.