Chemically Modified Carbon Nanocage As Electrode Materials Of Supercapacitor

As energy demand increases rapidly, the environmental and energy problem become more and more serious. It is great significance of developing high-performance, environmentally friendly, low-cost energy storage device such as supercapacitors. Electrode material is key factor for supercapacitor. The ideal electrode materials generally possess large specific surface area, good electrical conductivity and stability, suitable pore structure, good wettability, etc. Carbon materials have several desired features of electrode materials and then are widely used to supercapacitors. The surface characteristics of the carbon material has a great influence on the performance of electric double layer capacitor (EDLC). Our group reported a novel carbon nanocages (CNCs) as the excellent electrode materials of supercapacitors, which have the multiscale pore structure, high surface area, and good conductivity, etc. In this thesis, we have deeply investigated the influence of surface chemical modification on CNCs. Some progresses have been made.1. Enhancement of Surface Functionalization of CNCs for EDLC. The oxygen-containing functional groups can be introduced on the surface of CNCs with nitric acid oxidation method. The as-functionalized CNCs showed a significantly better performance than pure CNCs. The specific capacitance of CNC-6M reached 255 F g-1 and increased 34%, compared to 188 F g-1 of pure CNC at a current density of 1A g-1. At the same current densities, the specific capacitance of the as-functionalized CNCs were significantly higher than that of pristine CNCs. Namely, the surface functionalization for CNCs could obviously enhance the supercapacitor performance. At a high current density of 100 A g-1, the specific capacitance of as-oxidized CNCs still retained at the level of 111-167 F g-1, i.e., they exhibited good resistance to high current charge and discharge. After 10000 charging-discharging cycles at a current density of 10 A g-1, the specific capacitances of CNC-6M only dropped from 196 to 176 F g-1, namely, the functionalized CNCs possessed good cycle stability. The excellent supercapacitor performance of the as-functionalized CNCs was ascribed to the hierarchical pore structure, high surface area, good electrical conductivity of CNCs as well as the improved wettability and pseudocapacitance derived from the oxygen-containing functional groups.2. Effect of Phosphorus doping. Phosphorus-doped carbon nanocage (PCNCs) with different phosphorus content were prepared by CVD method. When the phosphorus content is lower than 1.0 at.%, the specitic capacitances increased significantly, compared with pure carbon nanocage. For 800P1CNC, at 1 A g-1 current density, the specific capacitances is up to 192 F g-1, increased 52% than that of 800CNC. But the further increase of phosphorus content, the specific capacitance decreased and are less than that of un-doped CNCs, which could be results from the reduction of electric conductivity.