Understanding RuO2·xH2O/carbon nanofibre composites as supercapacitor electrodes

Composites made from RuO2·xH2O particles supported on carbon nanofibres (CNF) have been prepared for supercapacitor electrodes. CNF, produced by Grupo Antolin Ing. SA. using a floating catalyst procedure was treated either in HCl or in HNO3. Then the composites were obtained by impregnation of CNF with an aqueous RuCl3·0.5H2O solution followed by filtering and alkali solution treatment. Heat treatment at 150 °C for 2 h was done. Specific capacitance of the composites has been measured and discussed on the basis of their RuO2·xH2O content and RuO2·xH2O particle size. The composites having RuO2·xH2O contents below 11 wt% show RuO2·xH2O particles, which grow from 2 to 4 nm as the RuO2·xH2O content increases. The specific capacitance of supported RuO2·xH2O, which can be very high (up to 840 F g−1), decreases as the RuO2·xH2O content increases and RuO2·xH2O particles grow. The composites having RuO2·xH2O contents above 11 wt% show RuO2·xH2O particles of nearly constant size (4 nm); the effect of increasing the RuO2·xH2O content is to increase the amount of particles but not the size of the particles. In these composites the specific capacitance of supported RuO2·xH2O is nearly constant (440 F g−1) and close to bare RuO2·xH2O (460 F g−1).