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.

Generation of hydrogen is one of the greatest challenges nowadays, especially chemically obtaining from the simple, straightforward borohydride hydrolysis reaction. Herein we are interested in this reaction for producing hydrogen using various nanocatalysts which are derived from graphene (reduced graphene oxide, rGO) and combined with metal-based nanoparticles (Ag, Ni and Ni(OH)₂). Overall, four promising catalysts were obtained using the liquid–liquid interfacial route in order to obtain highly homogeneous thin films. We highlight the novelty in employing thin films for the generation of hydrogen gas, in which the reaction kinetics was thoroughly elucidated, obeying first-order profiles. In fact, very high catalytic activity was observed using low amounts of nanocatalysts (∼0.1–0.8 mg), with the maximum rate of hydrogen production reaching nearly 33 × 10³ mL⁻¹ min⁻¹ g⁻¹. rGO/Ni nanocomposites are reported here for the first time, which also showed the most prominent activity. The isolated components alone were not efficient, evidencing the synergism in the nanocomposites produced. Finally, the nanocatalysts were recycled for up to 10 consecutive cycles, without losing activity. Various characterization techniques were performed during the reactions and after the reuse and confirmed that the typical nature of the composites remains intact.