Synthesis And Performance Of Manganese Oxide-based Supercapacitor Electrode Materials

Although many factors influence the electrochemical performances of the pseudocapacitive material, the rational structural design and the specific solution would be the key point for achieving breakthrough improvement. Manganese oxide has become a popular pseudocapacitive material for energy storage/conversion devices because of wide potential window, low-cost and environmentally benign properties, as well as the pivotal theoretical specific capacitance (1370 F g^-1). However, it faces the predicament after the boom of MnO₂/graphene composites. And there is still considerable debate regarding the explicit pseudocapacitive energy storage mechanism and ion/electron transfer process. In this thesis, innovative and scientific attempts were made to significantly improve the electrochemical performances of MnO₂-based electrode materials based on their essential characteristics and potential applications. ?1? The ingenious multiphase MnO₂ nanostructures were deliberately designed by a suitable Fe³⁺ doping process. Benefiting from the enhanced electrical conductivity and connected ion transport channels caused by the doping and acid erosion environment, the typical sample exhibits the boost pseudocapacitive performances, including the significantly improved specific capacitance, rate capability and cycle life ?100% maintained after 2000 cycles? compared to the pure MnO₂. The synergistic effects of alternative crystal structures, appropriate crystallinity and optimal morphology are identified to be responsible for the improvements. ?2? A nickel foam supported hierarchical mesoporous MnO₂/Ni?OH?₂ nanosheet architecture which exhibits exceptional capacitance and superb rate capability was successfully parepred by a facile one-step hydrothermal method. In the composite structure case, the synergistic effects are employed to study the competitive advantages of MnO₂/Ni?OH?₂@NF electrode, including highly conductive nickel foam substrate provides a fast electron transport pathway, and the hierarchical interconnected MnO₂/Ni?OH?₂ nanosheets ensures the fast diffusion of ions and the full use of the active materials. ?3? We pioneer a template-induced method to generate the ultrathin K-birnessite MnO₂ nanosheets based on a simple redox reaction. It is remarkable that sacrificial carbon template which comes from the carbonation of glucose on the cupper foam programs a interlaced self-assembling route, realizing a 3D self-supported network made up of mono/few layers. It would be reasonable to believe that the innovative delamination idea provides a basis for exploring a potentially transformative process to deal with the two-dimensional ?2D? layered materials. And these graphene-like mono/few layered productors display the peculiar surface properties, enhanced active sites and robust electrochemical performances-three times than the specific capacitance of ordinary MnO₂ nanosheets.