Preparation Of Starch-based Mesoporous Carbon And Its Electrochemical Performance

Energy issue has become a primary focus for the major world powers and scientificcommunity. There has been great interest in developing and refining more efficient energystorage devices. As one such device, the electrical double layer capacitor (EDLC) has maturedsignificantly over the last decade and emerged with the potential to facilitate major advancesin energy storage. As one kind of porous carbon materials, mesoporous carbon with manyvirtues including ordered pore structures, narrow pore size distributions, high specific surfacearea and chemical stability, can greatly improve the capacitance and cycle number of EDLC,which make it promising candidate for EDLC electrode material. The raw material andmethod to prepare mesoporous carbon are believed to play important roles on its porestructure and electrochemical performance.In this work, starch-based mesoporous carbons (SMCs) were prepared from solublestarch via simultaneous template method, and the technological method was studied to findthe optimum condition for the preparation of SMC with a high mesoporosity. On this basis,several technological conditions were changed to modify SMCs, and their influences on thepore structure and electrochemical performance of SMCs were also investigated. Finally,graphene oxide was added during different preparation steps to prepare the SMC-graphenecomposite, and the influence of graphene oxide on pore structure and electrochemicalperformance of starch-based mesoporous carbon was studied. The pore structure and surfacechemical property of SMCs and their composites were characterized by N2adsorption, SEM,TEM, and FT-IR. Galvanostatic charge-discharge, cyclic voltammetry (CV) andelectrochemical impedance spectroscopy (EIS) analyses were used to evaluate theelectrochemical performance of EDLC electrodes prepared from SMCs and their composites. The main results are as following.The optimized preparation parameters of SMC with high mesoporosity are as follows.The weight ratio of starch to P123is1to2, crystallization temperature is100°C, and thecarbonization temperature is850°C. Under such conditions, the BET surface area of SMC is1156.95m2/g, the mesoporosity is as high as94.95%. The obtained EDLC electrode fromSMC has better electrochemical performance. Its specific capacitance can be as high as144.08F/g at50mA/g of current density, and remains at127.47F/g even after1000cycles.The preliminary study on the impact of mesoporosity and BET surface area on theelectrochemical performance of SMCs has been carried out. When the mesoporosity (or BETsurface area) is similar, the higher the BET surface area (or mesoporosity) of SMCs, the betterthe electrochemical performance.Different steps to add starch, crystallization time and hydrochloric acid concentrationhave great impact on the pore structure and electrochemical performance of SMCs. Starchadded on the starting stage and appropriate crystallization time can prepare SMCs withplentiful pore structure and high electrochemical performance. High hydrochloric acidconcentration, which is conducive to the dissolution of P123, the hydrolyzation of starch andTEOS (tetraethoxysilane), can improve the self-assembly among starch, P123and TEOS.Consequently, the product displays more excellent morphology and performance.There are two ways to add graphene oxide in the preparation of graphene/starch-basedhybrids, i.e. pre-crystallization and past-crystallization, which can affect the structure andeletrochemical properties of the hybrids. The pre-crystallization process can make compositewith better pore structure and higher electrochemical property than those made by thepast-crystallization. Compared to SMC, the BET surface area and specfic capacitance of thepre-crystallization hybrid increased to1236.10m2/g from1156.95m2/g and to149.69F/gfrom144.08F/g, respectively.