Synergistic effect of surfactant and saccharin on dispersion and crystal refinement for electrodeposition of nanocrystalline nickel/graphene oxide composite

Homogeneous dispersion of graphene oxide (GO) in nickel sulfamate solution is a significant challenge for electrodepositing high-performance nickel/GO composite coatings. In the present work, three typical surfactants, including anionic surfactant Sodium dodecyl sulfate (SDS), cationic surfactant Cetyltrimethylammonium bromide (CTAB), and non-ionic surfactant Polyethylene glycol (PEG), and saccharin are used to disperse GO nanoparticles and refine crystallite size of nickel/GO composite coating. The synergistic effect of surfactant and saccharin is revealed from the perspectives of dispersion, crystal refinement and their impact on mechanical and tribological properties of nickel/GO composite coating. Our results indicate that PEG possesses the optimal dispersibility to GO dispersion, followed by CTAB and SDS. The addition of saccharin in electrolyte does not affect the surface charge of GO particles, but it helps to reduce the particle size of GO and thus reduce potential reaggregation. Additionally, PEG shows the most significant reduction of crystallite size from similar to 35 nm to similar to 19 nm. The synergetic effect of surfactant and saccharin is indicated by increasing the concentration of saccharin from 0 to 0.2 g/L with various surfactants, where the overall crystallite size is gradually reduced. Moreover, the hardness of PEG-GO and CTAB-GO coatings is remarkably increased by 252% and 312%, respectively, compared to pure nickel coating. The increased hardness is due to the synergistic effect of crystal refinement from both additions of GO and saccharin. The tribological test indicates that the PEG-GO coating can achieve the maximum reduction of friction coefficient with 0.15 with the addition of saccharin of 0.2 g/L.