Pseudocapacitive performance of Co(OH)2 enhanced by Ni(OH)2 formation on porous Ni/Cu electrode

A nanoflaky α-Co(OH)2 was cathodically deposited on a porous Ni/Cu electrode as an electrode material for supercapacitor. A three-dimensional porous electrode can accommodate more active materials and exhibits a higher specific capacitance and excellent high-rate stability. Unlike the smooth surface of the conventional Ni foam, the hydrogen templated porous Ni/Cu substrate had many microchannels and voids, which facilitated the adhesion of the deposited Co(OH)2 and improved the cycling performance. The porous α-Co(OH)2 film deposited on the porous electrode with a deposition charge of 1 coulomb (C) exhibited a specific capacitance as high as 1345 Fg−1 at 2 Ag−1 and even 1200 Fg−1 at a high rate of 40 Ag−1. With increasing the deposition amount from 1 to 5C, the area-specific capacitance apparently increased; however, the mass-specific capacitance gradually decreased. Notably, the porous electrode exhibited an excellent stability without significant loss after 3000 charge-discharge cycles, which was much better than those of the Ni foam and flat electrodes. It was attributed to the extra capacitance contribution of the Ni(OH)2 formation on the porous Ni/Cu electrode with high surface area. After the cycle test, the α-Co(OH)2 phase transformed to the β-Co(OH)2 and CoOOH. Moreover, the charge storage mechanism of the 1C-deposited Co(OH)2 on the porous electrode was suggested to be reaction-limited, rather than ion diffusion-controlled.