Carbon substrates, as previously reported, are colloidal carbon spheres (CCS) that contain oxygen-rich functional groups on the surface could that provide a suitable support for Co catalysts used for the hydrolysis of NaBH4. Our results show that the unmodified CCS substrate does not adequately interact with the Co2+ precursor to decrease the cobalt ion concentration in solution. However, after successful modification of the oxygen groups on the CCS substrate's surface, the Co ion concentration in solution decreased by 30% indicating interaction of the Co ions with the substrate surface. Also the cobalt dispersion and the hydrogen generation rate (HGR) for the catalysts supported on the modified substrate is much better than for the Co catalyst supported on the unmodified substrate. Therefore, the presence of oxygen on the substrate surface is not sufficient to provide a suitable dispersion and performance for nanocatalysts and modification of the surface leads to an improved catalyst. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.