Hydrogen storage mechanism in transition metal decorated graphene oxide: The symbiotic effect of oxygen groups and high layer spacing

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 2.3x, 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 nano particles 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. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.