Boron-Doped Graphene Directly Grown on Boron-Doped Diamond for High-Voltage Aqueous Supercapacitors

Boron-doped graphene/boron-doped diamond (BG/BDD) is synthesized by an electron-assisted hot-filament chemical vapor deposition (EA-HFCVD) method. Boron atoms are effectively doped into the graphene and diamond, and BG sheets are grown vertically on the BDD. The boron content of the BG affects the BG/BDD-electrode performance, and the electrode has a high specific capacitance when the BG is grown at a B-source-gas flow rate of 50 sccm. The electrochemical behavior of the BG/BDD electrode is analyzed in both positive and negative potential windows in three-electrode configurations using saturated aqueous NaCl as the electrolyte; a symmetric supercapacitor (SSC) is subsequently fabricated to evaluate the practical application of the BG/BDD electrode. The BG/BDD-based device operates at a high voltage of 3.2 V. The SSC delivers a high energy density of 79.5 Wh kg–1 at a power density of 221 W kg–1, and a high power density of 18.1 kW kg–1 at an energy density of 30.7 Wh kg–1; it also retains 99.6% of its specific capacitance in the 0–2.5 V (3.2 A g–1, 9000 cycles) voltage range and 96.1% in the 0–3 V (12.8 A g–1, 10 000 cycles) range; consequently, the device has a long-term stability advantage at high operating voltages.