Syntheses Of Mesoporous Materials And Their Supercapacitive Properties

Ordered mesoporous carbons (OMCs) have been recognized as good candidates of electrode materials for supercapacitors because of their high surface area, narrow pore size distribution and uniform pore connections. However, the specific capacitance of OMCs is still not satisfying. In this thesis, two strategies have been carried out to improve the charge storage properties of OMCs:one is increasing the specific surface area of OMCs by KOH activation; the other is incorporating other components which can provide high pseudocapacitance through redox reactions. In the last part, composite nanofibers of polyaniline (PANI) and manganese oxide have been fabricated via a triconstituent co-assembly method. More importantly, the composite with high specific surface area also possesses uniform mesopores constructed by the interlaced nanofibers.In chapter2, composites of PANI and a unique ordered mesoporous carbon MPC which possess small pores inside the carbon walls have been prepared. Small angle X-ray scattering (SAXS) patterns and transmission electron microscopy (TEM) images demonstrate that the ordered mesostucture is well retained after incorporation of PANI. N2sorption results reveale that in all of the PANI/MPC composites with PANI contents from22.3to55.5wt%, the small pores inside the carbon walls are gradually filled with the incorporated PANI, resulting in bicontinuous interpenetrating framework for the two components. Novel redox activities have been discovered for the PANI/MPC composites in a strong alkaline medium in negative potential range due to the efficient interaction between these two interpenetrating components. The maximum specific capacitance of the PANI/MPC composites is as high as400F/g at a high current density of1A/g in negative potential range (-0.7～0V vs. Hg/HgO) because of the pseudocapacitance generated by the redox reaction. Besides, as the vacancy in the pore walls is filled with PANI, the tap density of PANI/MPC composites is greatly enhanced. Therefore, the volumetric specific capacitance of PANI/MPC composites is2～5times higher than that of MPC. More importantly, the composite exhibits excellent rate capability due to its unique structure, with91%of capacitance retention when the discharging current density increases from1to20A/g.In chapter3, ordered mesoporous carbon-silica composite (CS) prepared by a triconstituent co-assembly method has been treated by KOH activation with various KOH/CS mass ratio (1:1,2:1and3:1) under750and850℃, respectively. During the activation process, the silica componet in the ordered mesoporous carbon-silica composite can be removed; meanwhile, the carbon walls can be gradually etched. Consequently, ordered mesoporous carbon with high specifc surface area can be obtained. When KOH/CS mass ratio is1:1,3～4.5wt%of silica is remained in the resulted samples. Upon increasing the KOH/CS mass ratio to2:1, the amount of residual silica in the resulted samples is1.2～1.8wt%, which is similar to that of HF treated sample. However, when the KOH/CS mass ratio further increase to3:1, the amount of residual silica increase obviously due to the destruction of mesostructure. SAXS patterns and TEM images suggest that the mesostructural regularity of the activated samples gradually degrades along with increase of KOH/CS mass ration as well as activated temperature. N2sorption results show that KOH activation leads to significant enhancement in specific surface area and a higher KOH/CS mass ratio results in larger surface area. However, the specific surface area of sample CSK-850-3which is activated with a mass ratio of3:1under850℃decreases obviously because of destruction of mesotructure and high silica residual amount. The specific capacitance of ordered mesoporous carbons obtained by KOH activation is enhanced efficiently compared with HF treated sample in6M KOH solution, and the variation of specific capacitance is accordant with that of specific area.In chapter4, in oreder to get mesoporous carbon materials with high specific surface area as well as highly ordered mesostucture, ordered mesoporous carbon-silica composite (CS) has been hydrothermally treated by6M KOH at200℃for12,24and48h, respectively. SAXS patterns demonstrate that the resulted samples CSK-200-12, CSK-200-24and CSK-200-48all remained well ordered mesostructure. For CSK-200-12, ca.8wt%of silica is remained, while for CSK-200-24and CSK-200-48, the silica component can be removed successfully. N2sorption results reveal that CSK-200-24has the highest specific surface area. Therefore, we chose CSK-200-24as the host and load different amount (14.3,23.4and34.5wt%) of MnO2via in-situ oxidation between carbon walls and KMnO4neutral solutions. The mesostructural regularity of the composite materials gradually degrade along with increase of MnO2amount, and the mesostructure of composite with34.5wt%of MnO2is completely destroyed. Thanks to the high pseudocapacitance contributed from MnO2, the composites exhibited higher specific capacitance in1M Na2SO4solution than that of order mesoporous carbon host CSK-200-24. Upon loading14.3%MnO2, the specific capacitance of the related composite increase39%compared with CSK-200-24, and the specific capacitance of the composite increases along with the increase of MnO2amount. When the MnO2amount is not higher than23.4wt%, the composites showed good rate capability, when the MnO2amount increases to34.5wt%, the rate capability of the related sample is poor owing to the destruction of mesostructure.In chapter5, composite nanofibers of PANI and MnO2has been fabricated by a triconstituent co-assembly method, wherein anion surfactant sodium dodecyl sulfate is used as structure director, KMnO4is used as the oxidant to initiate the polymerization of aniline, and KMnO4is reduced to MnO2at the same time. The resulted PANI-MnO2nanofibers construct large mesopores (12nm), which generated high surface area (210m2/g) and large pore volume (0.41cm3/g). The large mesopores and the one dimensional nanostructure facilitate good rate capability in1M Na2SO4solution, with80%of capacitance retention when the discharging current density increases from1to5A/g.