One material, multiple functions: graphene/Ni(OH)₂ thin films applied in batteries, electrochromism and sensors

Different nanocomposites between reduced graphene oxide (rGO) and Ni(OH)₂ nanoparticles were synthesized through modifications in the polyol method (starting from graphene oxide (GO) dispersion in ethylene glycol and nickel acetate), processed as thin films through the liquid-liquid interfacial route, homogeneously deposited over transparent electrodes and spectroscopically, microscopically and electrochemically characterized. The thin and transparent nanocomposite films (112 to 513 nm thickness, 62.6 to 19.9% transmittance at 550 nm) consist of α-Ni(OH)₂ nanoparticles (mean diameter of 4.9 nm) homogeneously decorating the rGO sheets. As a control sample, neat Ni(OH)₂ was prepared in the same way, consisting of porous nanoparticles with diameter ranging from 30 to 80 nm. The nanocomposite thin films present multifunctionality and they were applied as electrodes to alkaline batteries, as electrochromic material and as active component to electrochemical sensor to glycerol. In all the cases the nanocomposite films presented better performances when compared to the neat Ni(OH)₂ nanoparticles, showing energy and power of 43.7 W h kg^-1 and 4.8 kW kg^-1 (8.24 A g^-1) respectively, electrochromic efficiency reaching 70 cm² C^-1 and limit of detection as low as 15.4 ± 1.2 μmol L^-1.