Fig xA Voltammograms of graphene
Graphene-metal oxide composites exhibit great potential for application in ECs due to their improved electrical conductivity, large specific surface area and excellent electrochemical stability , ,  and .
2.1. Preparation of [email protected] composite films supported on nickel foams
GO was synthesized according to previous reports  and . In a typical process, 40 mg GO and 248 mg nickel acetate were dissolved in 1,2-propylene glycol and transferred to a syringe. The nickel foam substrate was heated to 250 °C.