Doped Carbon Nanocages As Supercapacitor Electrode Materials

As a new type of energy storage devices, supercapacitor has the advantages of high power density, long cycle life, short charged time, high reliability and environmental benignity. It is thus promising to be widely used in consumer electronics products, memory backup systems, industrial power and energy management systems.Carbon materials have rich structures and morphologies, such as activated carbon, mesoporous carbon, carbon nanofibers, carbon nanotubes, graphene, and so on. As an ideal supercapacitor electrode materials, carbon materials also have relatively low cost. They are thus the most widely used electrode materials. However, the conventional carbon materials based supercapacitors have the problems that the specific capacitance decreases dramatically with increasing the charging-discharging rate. Recently, our group have developed a new method to prepare carbon nanocages (CNCs), which have high specific surface, regular pore structures, and good conductivity. As supercapacitor electrode materials, CNCs show superior performance to activated carbon and mesoporous carbon.Introducing surface functional groups or doping heteroatoms into carbon materials can enhance the wettability and then improve the capacitance. In this thesis, doped carbon nanocages were controllably prepared and their supercapacitor performance were investigated. The main results are listed below:(i) N-doped carbon nanocages (NCNCs). NCNCs were controllably prepared using pyridine as precursors and magnesium oxide as template, which have high specific surface area (1692m2/g) and nitrogen content (10at%). The specific surface, pore size, and nitrogen content can be regulated by controlling the synthesis temperature. As supercapacitor electrode materials, NCNCs present good performance in acid and basic aqueous solution. The maximum specific capacitance is up to367F/g at the current density (Id) of1A/g. Noticeably, the specific capacitance of NCNC800can still keep259and112F/g at Id of10and100A/g, respectively. This is obviously superior to that of CNC800. This result indicates that the introduction of nitrogen could improve the wettability and the adsorption sites for ions on the surface of NCNCs.(ii) B, N co-doped carbon nanocages (BNCNCs). BNCNCs were controllably prepared using the mixture of DMAB and pyridine as precursors and magnesium oxide as template, which have high specific surface area (1319m2/g), boron and nitrogen content (B:4.5at%, N:11at%). The specific surface, pore size, boron and nitrogen content of BNCNCs could be regulated by adjusting the synthesis temperature and the concentrations of precursors. As supercapacitor electrode materials, BNCNCs present good performance in acid and basic aqueous solution. The maximum specific capacitance reaches369F/g at Id of1A/g. The specific capacitance of BNCNC700-1can still keep217and143F/g at Id of10and100A/g, respectively. This is much superior to that of CNC700and NCNC700. It could be attributed to the introduction of boron and nitrogen dopants.