Effect of alkaline electrolytes on the charge storage capacity and morphology of porous layered double cobalt hydroxide-coated graphene supercapacitor electrodes

Abstract

Although alpha-cobalt hydroxide (α-Co(OH)₂) with a layered double hydroxide (LDH) structure has been widely used as a supercapacitor electrode, the effect of an alkaline electrolyte on the charge storage performance of the α-Co(OH)₂ has not yet been investigated. In this work, α-Co(OH)₂ was electrodeposited on reduced graphene oxide-coated carbon fiber paper (rGO/CFP) using chronoamperometry at −0.5 V vs. Ag/AgCl. The effect of alkaline aqueous electrolytes on the performance of the α-Co(OH)₂/rGO/CFP electrodes was then investigated by means of scanning and transmission electron microscopies, X-ray photoelectron and absorption spectroscopies, and electrochemical techniques. It was found that the concentrated alkaline electrolytes (i.e., 3–6 M [OH⁻]) can strip off and/or deform the porous structure of the α-Co(OH)₂ deposited on rGO/CFP leading to poor charge storage capacity. 1 M [OH⁻] was found to be a suitable electrolyte concentration providing high specific capacitance (1096 F g⁻¹ at 1.8 A g⁻¹) without the deformation of the porous α-Co(OH)₂ structure after testing. Morphological and electrochemical analyses of the α-Co(OH)₂/rGO/CFP electrodes suggest that the effect of the alkaline electrolyte concentration plays a major role on the charge storage performance of α-Co(OH)₂-based supercapacitors.