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Transition metal nanoparticle decoration is widely used to enhance the hydrogen storage properties of carbon materials. However, little efforts have been devoted to unveil structural interaction between nanoparticles and substrate and understand the underlying kinetic mechanism for hydrogen sorption. In this work, a suite of TiO2 nanoparticles decorated graphene oxide (GO) composites is fabricated and characterized to determine the interactions between material structure and hydrogen storage kinetics. EELS and XPS results show that interactions between nanoparticles and GO cause changes of the chemical states of C–O, C O and C–OH groups; furthermore, reactions of C–OH, HO–C O and C–O–C groups with TiO2 nanoparticles create C–Ti and Ti–O–C bonding. Decoration of TiO2 nanoparticles improves the capacity of GO by 2.3×, and 80% of the adsorption is reversible. By means of semi-empirical kinetic analysis, it is determined that hydrogen adsorption is controlled by two-dimensional diffusion regardless of layer spacing; while desorption is controlled by multiple diffusion processes and is sensitive to layer spacing. Collectively, these new findings deepen the understanding of transition metal nanoparticles decorated GO materials in the aspects of nanoparticle incorporation and hydrogen storage kinetic mechanism. In particular, oxygen groups enhance nanoparticle decoration, while high layer spacing improves desorption kinetics and reversibility.

In this work, two kinds of novel manganese decorated (G + Mn) and manganese-vanadium co-decorated (G + MnV) graphene composites are synthesized by in situ wet chemical reduction, and their hydrogen storage properties and microstructures are characterized by Sievert-type adsorption apparatus, BET, SEM, TEM/STEM, EDX and EELS. Compared with pristine graphene, Mn decoration marginally increases the hydrogen adsorption capacity of graphene at room temperature and 4 MPa hydrogen pressure from 0.25 wt% to 0.36 wt%. On the other hand, the co-decoration of Mn and V increases the room temperature hydrogen storage capacity of graphene significantly to 1.81 wt% under 4 MPa hydrogen pressure, which is 1.56 wt% higher than the capacity of pristine graphene. The microstructures and valence states of the decorated Mn and Mn-V nanoparticles are investigated by TEM, EDX and EELS analyses, and strong interactions between the decorated nanoparticles and graphene are observed. Based on the results from structural analyses, potential enhancement mechanisms are suggested in terms of the catalytic effects of nanoparticles on graphene hydrogen adsorption. Given the relatively low cost of Mn and V metals compared to noble metals such as Pd, Pt and Au, these results demonstrate a low cost and effective way to significantly enhance the room temperature hydrogen adsorption properties of graphene for potential hydrogen storage applications.