Formation of nano-scaled crevices and spacers in NiO-attached graphene oxide nanosheets for supercapacitors

Graphene oxide nanosheets were deposited directly onto the stainless steel substrate using electrophoretic deposition (EPD). The nickel ions adsorbed at the graphene oxide surface were reduced electrochemically to form nickel nanoparticles during the EPD process in the presence of a nickel nitrate additive. The attached Ni nanoparticles converted to NiO nanoparticles after annealing at 300 degrees C. The NiO nanoparticles functioned as nanospacers to improve the face-to-face aggregation of the graphene oxide sheets. The nano-scaled crevices could be formed in the NiO-attached graphene oxide electrode after heat treatment due to different shrinkage or expansion rates between the graphene oxide and NiO nanoparticles. The wettability of electrode might be improved by the deposition of hydrophilic NiO nanoparticles at the surface of graphene sheets. Therefore, the specific capacitance of the NiO-attached graphene oxide reached as high as 569 F g(-1), which is 40 times higher than that of the bare graphene oxide electrode (13 F g(-1)) at a discharge current density of 5 A g(-1).