Hybrid supercapacitors from porous boron-doped diamond with water-soluble redox electrolyte

Abstract Hybrid supercapacitors (HSCs) can simultaneously achieve battery-level energy as well as capacitor-level power and cycle life in a single device. To construct such HSCs, porous boron-doped diamond (BDD) films fabricated by a template-free method via regrowth of diamond nanoparticles were employed as the electrodes and water-soluble redox couples (Fe (CN)63−/4−) as the electrolyte. For the three-electrode system, the porous BDD electrode delivers a capacitance of 13.08 mF cm−2 in 1.0 M Na2SO4, and a capacity of 78.23 mAh g−1 in 0.05 M Fe (CN)63−/4− + 1.0 M Na2SO4 when a scan rate of 10 mV s−1 is applied. For the symmetric two-electrode system, the porous BDD electrode exhibits a capacitance of 13.04 mF cm−2 in 1.0 M Na2SO4 and a capacity of 34.74 mAh g−1 in 0.05 M Fe (CN)63−/4− + 1.0 M Na2SO4 at the same scan rate. The capacitance (capacity) remains about 92% of its initial value after 5000 cyclic voltammetry cycles in all conditions. The specific power densities (normalized by the mass of electrode active material only) are 0.17 and 1.05 kW kg−1, with their specific energy densities of 5.51 and 38.10 W h kg−1, respectively. Thus, the porous BDD films, together with the water-soluble redox electrolyte, have profound applications in high-performance hybrid supercapacitors construction for future power devices.