Preparation And Electrochemical Properties Of Hierarchical Biomass Carbon And Metal Oxide Materials

The increasingly serious energy and environmental problems forced researchers continue to develop new energy storage devices in modern society. Developing high efficiency electrochemical supercapacitor devices is considered as an attractive route to keep the balance between energy resources and environment. Because of electrode materials play a decisive role on the performance of the supercapacitor, as a result, design and preparation of high-performance electrode material is an effective way to improve the performance of supercapacitorsHere, we have successfully prepared a kind of hierarchical and high-performance porous biomass carbon material by using some traditional materials synthesis means. In addition, we have also synthesised biomass carbon-based binary manganese dioxide composite by combining the as-prepared porous biomass carbon with high theoretical specific capacity manganese dioxide. Some symmetric and asymmetric supercapacitors with a high operating voltage had been designed and assembled. The practical value and electrochemical properties of two-electrode systems were systematic evaluated.We successfully employed a green dipping and subsequent heat treatment method to synthesize hierarchical and interpenetrating 3D hollow MnO2/C composites from natural porous lotus pollen grains as both the skeleton and carbon source, and explore the potential of the electrode material for supercapacitors. We did obtain the optimal experimental condition by studying the influence of different reaction and calcination time on morphology and electrochemical properties of the MnO2/C composite. Benefiting from the synergistic effect between manganese dioxide and the porous carbon matrix, the MnO2/C-3 composite has a high specific capacitance of 257 F/g at a current density of 0.5 A/g. And, the specific capacitance and Coulombic efficiency of MnO2/C-3 composite still retains as high as 88%and 94% of its maximum after charge/discharge 2000 cycles at 4 A/g, respectively. More importantly, the as-assembled asymmetric supercapacitors based on MnO2/C-3 composite and AC can deliver a high nergy density of 18 Wh/kg at a power density of 810 W/kg and still maintains 7 Wh/kg at a high power density of 9000 W/kg.Then, we have successfully synthesized heteroatom-functionalized porous graphitic carbonaceous materials with 3D hierarchical and interconnected honeycomb-like structure by using waste biomass pomelo peel as raw material through the combination of hydrothermal carbonization and followed KOH activation procedure. Effects of hydrothermal conditions,KOH concentration, activation temperature and other experimental parameters were systematically studied on the morphology of the biomass carbon, surface oxygen functional groups and electrochemical performances. The HPGC-4 material shows a high specific surface area of 832 m2/g. And the surface oxygen content of HPGC-4 is 20.32 at % (XPS O1s). The partial graphitization structure and interconnected pore network resulting in high specific capacitance of 374 F/g at a current density of 0.1 A/g and good cycling stability with 92.5% of initial capacitance retained after 5000 cycles. Moreover, the assembled symmetrical supercapacitor based on HPGC-4 electrode material exhibits a high gravimetric energy density of 20 Wh/kg at a power density of 400 W/kg (based on the total mass of the active materials of the two electrodes). The MnO2/HPGC-4 composite based on HPGC-4 has a high specific capacity of 326.1 F/g at 0.5 A/g. Furthermore, the maximum energy density of assembled MnO2/HPGC-4//HPGC-4 symmetric supercapacitor is 21 Wh/kg.