Fabrication And Electrochemical Properties Of Mesoporous Carbon-based Nanocomposites

Supercapacitors are green and novel energy storage devices, which fill the gap between conventional capacitors and batteries. At present, there exists the disadvantage of relatively low energy density for commercial supercapacitors. To meet with the increasing development of electric vehicles, backup systems and military applications, it is urgent to further enhance the energy density, power density and cycle stability of supercapacitors. Electrode material is crucial to the performance of supercapacitors. And the preparation of high performance electrode material is hot and difficult problem in the present study. For this reason, this paper will combine carbon with long cycle life and conducting polymer or metal oxide with high specific capacitance and carry out the research on the design, structure control and preparation of mesoporous carbon loaded with conducting polymer or metal oxide. It is expected to develop the synergistic effect between two components by optimizing the structure of composites at the nanoscale and to improve the electrochemical performance of composite electrodes greatly. Main contents in this paper are shown as follows:1. Polyaniline nanowhiskers (PANI-NWs) were grown on the outer surface of mesoporous carbon (CMK-3) with ordered mesoporous silica/carbon compounds as carriers by chemical oxidative polymerization. This composite overcomes the very low surface area drawback in its similar composites and can develop the electric double layer capacitance of CMK-3effectively to improve the electrochemical properties of composites. In this experiment, camphorsulfonic acid (CSA) was used as the dopant to prepare PANI-NWs/CMK-3composites on the premise of retaining mesoporous channels. The reserved mesopores and PANI-NWs endow the composite with a high surface area of497m2g-1. The specific capacitance of the hierarchical composite is470F g-1and retains90.4%after1000cycles.2. PANI/CMK-3/MnO2ternary composites that couple with CMK-3, PANI and MnO2were obtained via chemical oxidative polymerization in combination with redox reaction. Electrochemical measurements indicated the ternary composite with12wt%MnO2possessed the highest specific capacitance. PANI nanolayer was uniformly coated on the surface of matrix particles. As the protective skin, PANI can effectively restrain MnO2nanoparticles from reductive-dissolution process and enhance their electrochemical utilization in acidic electrolyte. The specific capacitance of PANI/CMK-3/MnO2is significantly higher than pure PANI and PANI/CMK-3binary composite. After CMK-3is modified with MnO2nanoparticles and PANI nanolayer simultaneously, the synergistic effect among three components can be greatly developed to improve the electrochemical properties of the ternary composites.3. Novel PANI/OBMC composites were designed and synthesized to combine the ordered bimodal mesoporous carbon (OBMC) with superior charge-discharge performance and one-dimensional PANI nanostructure with excellent conductivity and electrochemical property. Structural and morphological characterizations indicated that the polyaniline nanowire arrays with20-30nm diameters were grown on the surface of OBMC. The bimodal pore distribution and hierarchical structure endow the PANI/OBMC composite with a high surface area of599m2g-1. The hierarchical composite with60wt%PANI possesses the highest specific capacitance of517F g-1and outstanding cycling stability with a capacitance retention of91.5%after1000cycles. The coexistence of primary mesopores and abundant small mesopores is in favor of the fast penetration of electrolyte and the unique hierarchical structure facilitates the ion diffusion and shortens the charge transfer distance, which lead to the superior electrochemical performance of PANI/OBMC-60%.4. Mesoporous carbon nanosheets (MCNs) with interconnected structure were synthesized using porous MgO layer as the template and resol as the carbon source. The morphology of the mesoporous carbon particles can be easily controlled by altering mass ratio of MgO to resol. The interlaced MCNs can be formed when the mass ratio of MgO/resol is1/1. The quantities of mesopores and micropores endow the MCNs with large surface area of1180m2g-1and high pore volume of1.56cm3g-1. The electrochemical measurement results show that the interlaced MCNs exhibit the highest specific capacitance of241F g-1and the best rate capability.5. MnO2/FMCNs hierarchical composites were successfully prepared by redox reaction with functionalized mesoporous carbon nanosheets (FMCNs) as matrix. Then a new asymmetric supercapacitor based on MnO2/FMCNs and FMCNs as positive and negative electrode was assembled. This asymmetric supercapacitor can be stable in1M Na2SO4electrolyte even at the potential window up to2.0V. The energy density can reach up to44.81Wh kg-1at a power density of100W kg-1, and still remain9.72Wh kg-1at a power density of5000W kg-1, which is higher than those of other MnO2-based asymmetric supercapacitors reported in the literature.