Electrochemical Supercapacitors from Diamond

Boron-doped diamond has been utilized as an electrode material to construct an electric double layer capacitor (EDLC) as well as an electrode support to form a pseudocapacitor. In 1.0 M NaSO 4 solution, the capacitance of diamond EDLC is in the range of 3.6–7.0 μF cm –2, comparable with those of EDLCs based on other carbon materials. During a charge/discharge process for 1000 cycles at a scan rate of 100 mV s –1, the capacitance only decreases 5%, indicating high stability and a long lifetime of such an EDLC. To improve the capacitance of diamond EDLCs, diamond was coated with a MnO 2 film to construct a pseudosupercapacitor. The MnO 2 films were electrodeposited at a constant potential of 0.9 V vs Ag/AgCl in 0.2 M MnSO 4 solution. The mass of MnO 2 deposited per unit area, called the area density, calculated from the deposition charge, was controlled via the deposition time. The MnO 2 films were characterized using various techniques like SEM, XPS, Raman spectroscopy, etc. In 1.0 M NaSO 4 solution, the capacitance of the MnO 2 /diamond-based pseudosupercapacitor rises with an increase of the mass of MnO 2 on diamond. Its maximum capacitance was found to be reached at a MnO 2 area density of 24 μg cm –2 . The capacitance obtained from voltammetry is 384 μF, or 326 F g –1 at a scan rate of 10 mV s –1, which is comparable with the value of 406 μF, or 349 F g –1, obtained from charge/discharge process at a current density of 3 A g –1 in the potential range 0 to 0.8 V. The capacitance was reduced by 34% after 1000 subsequent charge/discharge cycles carried out at a scan range of 100 mV s –1 . The comparison of the performance of the MnO 2 /diamond pseudosupercapacitor with that of those pseudosupercapacitors based on MnO 2 and other carbon materials indicates that diamond could be suitable for electrochemical supercapacitor applications.