  Battery-like supercapacitors feature high power and energy densities as well
as long-term capacitance retention. The utilized capacitor electrodes are thus
better to have large surface areas, high conductivity, high stability, and
importantly be of binder free. Herein, vertically aligned carbon nanofibers
(CNFs) coated boron-doped diamonds (BDD) are employed as the capacitor
electrodes to construct battery-like supercapacitors. Grown via a thermal
chemical vapor deposition technique, these CNFs/BDD hybrid films are binder
free and own porous structures, resulting in large surface areas. Meanwhile,
the containment of graphene layers and copper metal catalysts inside CNFs/BDD
leads to their high conductivity. Electric double layer capacitors (EDLCs) and
pseudocapacitors (PCs) are then constructed in the inert electrolyte (1.0 M
H2SO4 solution) and in the redox-active electrolyte (1.0 M Na2SO4 + 0.05 M
Fe(CN)63-/4-), respectively. For assembled two-electrode symmetrical
supercapacitor devices, the capacitances of EDLC and PC devices reach 30 and 48
mF cm-2 at 10 mV s-1, respectively. They remain constant even after 10 000
cycles. The power densities are 27.3 kW kg-1 and 25.3 kW kg-1 for EDLC and PC
devices, together with their energy densities of 22.9 Wh kg-1 and 44.1 Wh kg-1,
respectively. The performance of formed EDLC and PC devices is comparable to
market-available batteries. Therefore, the vertically aligned CNFs/BDD hybrid
film is a suitable capacitor electrode material to construct high-performance
battery-like and industry-orientated supercapacitors for flexible power
devices.
