Controllable synthesis of Ni(OH)2/Co(OH)2 hollow nanohexagons wrapped in reduced graphene oxide for supercapacitors

Abstract

Reduced graphene oxide (rGO) wrapped hollow nanohexagons comprised of nickel hydroxide and cobalt hydroxide have been synthesized via in situ wet chemical approach. The 3D structure comprised of rGO and Co, Ni–OH can improve the electron transport ability and increase the contact of the active sites with electrolyte. The Ni(OH)₂/Co(OH)₂ hollow nanohexagons are uniform with outer diameter of ∼200 nm and inner diameter of ∼150 nm. The electrochemical performance of Ni(OH)₂/Co(OH)₂ hollow nanohexagon wrapped by rGO can be readily manipulated by adjusting the ratio between Ni, Co precursors and graphene oxide. High specific capacitance with enhanced electrochemical properties is attributed to the conductive network provided by graphene and synergetic effect between graphene and other components in electroactive material. Specially, the Ni(OH)₂/Co(OH)₂ hollow nanohexagon with 1.0 μg mL⁻¹ rGO exhibits a maximum specific capacitance of 1292.79 F g⁻¹. Meanwhile, such sample also exhibit smaller equivalent series resistance and charge transfer resistance compared with hollow hexagons wrapped by other rGO concentrations. Cycling performance performed at 5 A g⁻¹ shows that after 2500 cycles, the capacitance can still maintain 85.9% of the maximum.