One-pot electrochemical assembling of porous cobalt hydroxide/nitrogen-doped porous graphene onto Ni foam as a binder-free electrode for supercapacitor applications

Abstract

• N-doped porous graphene was synthesized through catalytic-assisted chemical vapor deposition method. • The binder-free Co(OH) 2 @N-doped graphene/Ni foam was prepared through one-pot deposition strategy. • Specific capacitances as high as 1907 f g –1 and cycling retention of 95.9% after 4000 consecutive cycles at 2 a g − 1 . • Full synergetic contribution between EDL and pseudocapacitive based charge storing behaviors was observed. In this paper, cobalt hydroxide nanoplates/nitrogen-doped porous graphene (Co(OH) 2 @NPG) nanocomposite were deposited onto Ni foam through a facile co-electrodeposition route, and the charge storage capability of the fabricated Co(OH) 2 @NPG/NF was evaluated as a binder-free supercapacitor electrode. The co-deposition of cobalt hydroxide/N-doped porous graphene was carried out, for the first time, from a NPG dispersed aqueous electrolyte containing 5 mM cobalt nitrate. The characterization techniques of XRD, IR, FE-SEM, BET, Raman and TG proved uniform deposition of hexagonal β-Co(OH) 2 nanoplates onto N-doped porous graphene electrophoretically deposited onto Ni foam surface. Raman spectroscopy results confirmed the charge transfer between NPG and cobalt hydroxide through red shift in comparison to single analogous material. The prepared composite powder exhibited enhanced surface area as compared with pristine hydroxide powder (285.716 m²/g vs. 185.2 m²/g), where composite material showed mesoporous texture with IV hysteresis loop isotherm. Furthermore, the Co(OH) 2 /NPG electrode exhibited specific capacity of 1144 C g − 1 and cycling retention of 95.9% after 4000 consecutive cycles at 2 A g − 1 as well as 86.8% after 4000 consecutive cycles at 8 A g − 1 whereas the single analogous cobalt hydroxide deposited onto Ni foam showed specific capacity of 798 C g –1 and capacity stabilities of 83.4% and 60.1% after 4000 cycles at 2 and 8 A g − 1 . The improved electrochemical performance in comparison to Co(OH) 2 /NPG nanocomposite electrode was ascribed to the full accessibility of Co(OH) 2 active material over large surface area of N-doped graphene for fast charge transportation and synergetic contribution between electric double layer and pseudocapacitive based charge storing in composite form.