Electrophoretic deposition of RGO-NiO core-shell nanostructures driven by heterocoagulation method with high electrochemical performance

A heterocoagulation route is proposed to prepare Reduced Graphene Oxide-Nickel Oxide (RGO/NiO) hybrid structures for their application as supercapacitor electrodes. The RGO intercalation among the NiO nanoplatelets was carried out by electrostatic interactions of the synthetized particles which were previously dispersed and stabilized in aqueous media to improve the assembly between both materials forming core-shell structures. The electrophoretic deposition (EPD) was used to shape the composite onto 3D collector (Ni foams) controlling their growth and homogeneity. Electrodes were thermal treated at 325 °C during 1 h to improve the electrochemical response since the formation of ceramic necks among NiO semiconductor nanoparticles preserves the microstructural integrity to enhance their connectivity avoiding the employment of binders, while RGO contributes with the electrochemical double layer effect to step up the specific capacitance by reducing the charge transfer resistance. FESEM results confirmed that RGO nanosheets were full-covered by the NiO nanoplatelets and suggested that ∼1 mg of the electroactive composite homogeneously covers the Ni foam and it is the optimum among of electroactive material to avoid microstructural defects that produce ohmic drops limiting the capacitance. The electrochemical characterization of the resulting binder-free RGO/NiO electrodes was compared with the bare-NiO electrode. The hybrid composite exhibited excellent performance with a high specific capacitance of 940 F g-1 at 2 Ag-1 and a higher rate capability.