Preparation And Electrochemical Properties Of Bir-MnO₂/r GO Composite

Electrochemical supercapacitor is a new energy storage equipment and component between batteries and electrostatic capacitors, which has higher energy density than that of electorstatic capacitor and higher power density than that of batteries. The performances of ECshave close relationship to the quality of the active materials used in electrodes. Birnessite-type manganese dioxide（Bir-MnO₂） as electrode materials for supercapacitor has many advantages such as high specific capacitance, low cost, environmental friendly and abundance in nature. Nevertheless, it also has shortcomings like poor electronic conductivity and partial dissolution, thus less utilization of MnO₂ in most cases. To meet the demands of the high electrochemical performance, the combination of birnessite MnO₂ nanostructures with other materials such as graphene, mesoporous carbons has attracted many attentions. Graphene has tremendous attraction such as high electrical, large specific surface area, and superior mechanical strength. Graphene can incorporate MnO 2 nanosheets on its conductive support to optimize the electrochemical performance of MnO₂. Based on above ideas, our groups have designed and synthetized Bir-MnO₂/rGO nanomaterial for supercapacitor, which have exhibited remarkably improved electrochemical performance. So it is important to deeply study and investigated growth mechanism of the hybrid. In this work, we mainly controlled the reaction time to illustrate the relationships between morphology and excellent electrochemical properties.1. Bir-MnO₂/rGO nanomaterial with a unique structure of porous birnessite-type manganese dioxidenanosheets on graphene has been synthesized by a simple hydro thermal method. We prepared products based on a series of time-dependent experiments such as 1/2h, 1h, 3h, 6h and 12 h to discuss the formation mechanism of the hybrid. The relationships between structure, morphology and excellent electrochemical properties of these materials were investigated by comparison. Then, we concluded the law and give the results. The results show that the rate capability, specific capacity and cycle life of bir-MnO₂/rGO nanomaterial are getting better with the extension of reaction time. The specific capacitance of the five composite electrode materials are: 105.6, 106.4, 142.5, 168.6, and 173.9 F/g when the current density is 0.5 A/g. Moreover, the capacitance of the electrodes are 52.6%, 69.7%, 77.1%, 80.5% and 80.8% retained after 2000 cycles at a charging rate of 2 A g-1 respectively. The hybrid with a reaction time of 6h showed the best electrochemical performances.2.We developed a facile and robust method for fabricating mesoporous microporous three-dimensional composite porous carbon material, in which CTAB as soft template of mesopores, silica nanospheres as hard template of macropores and phenolic resin oligomer as carbon precursor. We further fabricate the three-dimensional pore structureswith different porosity and pore connectivity and study on the corresponding electrochemical properties. Results show that the three-dimensional composite porous carbon material has a highly ordered holes structure with thin carbon support and its aperture is about 120 nm. The specific capacitance of the 3D network structure is 54 Fg-1 under 0.2 A/g and is slightly less than the specific capacitance of rGO. Furthemore, a long cycle life with the capacitance retention ratio of 88.6% at 2A g-1 after 2,000 cycles. Moreover, the EIS measurements demonstrated the equivalent series resistance of the 3D network structure is about 1.6Ω and the relaxation time is less than 1 s, which shows good electric double layer capacitance.