Graphene/nickel nanoparticles composites from graphenide solutions.

Nanocomposites between nickel nanoparticles and graphene were obtained starting from nickel cations and graphenide solutions (negatively charged graphene layers) as both reducing agent to nickel cations and graphene source. Different nanomaterials were obtained in two different solvents, N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF), with different nickel/graphene ratios. The nanomaterials were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). All the samples consist of large graphene layers highly decorated with crystalline nickel nanoparticles, of size ranging from 2 to 10 nm. Thin films of the samples were deposited on indium-tin oxide (ITO) substrates and electrochemically characterized in alkaline medium, leading to Ni(OH)2/NiOOH redox pair, where the increase of the nickel proportion in the nanocomposites resulted in higher peak currents. The samples obtained in NMP showed the best performance with a fivefold increase of the peak currents, consistent with the lower charge transfer resistance as seen by electrochemical impedance spectroscopy (EIS).