Design and Electrochemical Study of Three-Dimensional Expanded Graphite and Reduced Graphene Oxide Nanocomposites Decorated with Pd Nanoparticles for Hydrogen Storage

The development of efficient and low-cost solid-state hydrogen storage materials remains a significant challenge. Carbonaceous-based nanostructures supported with metal catalysts have shown promising results toward hydrogen storage. Here, we report on a facile one-pot synthesis of a novel three-dimensional (3D) reduced graphene oxide (rGO) and expanded graphite (EG) nanocomposite (NC) decorated with Pd nanoparticles (NPs) as hydrogen storage media. The effects of the electrochemically active surface area and surface oxygen groups of the as-synthesized Pd/rGO-EG on electrochemical hydrogen uptake and release were investigated in detail. For comparison, five Pd/rGO-EG NCs with rGO/EG mass ratios of 3:1, 2:1, 1:1, 1:2, and 1:3 were prepared. All the Pd/rGO-EG NCs exhibited a much higher hydrogen storage capacity than Pd/rGO and Pd/EG. Among them, Pd/rGO-EG(1:1) showed the highest hydrogen uptake and release (9850 mC cm–2 mg–1), which was over six- and twofold increase compared to Pd/rGO (1480 mC cm–2 mg–1) and Pd/EG (4290 mC cm–2 mg–1), respectively. The synergistic effects of the rGO-EG NC could be attributed to the formation of the 3D graphene-based structure, a minimal degree of sheet stacking, and homogeneous Pd NP dispersion. The formed Pd/rGO-EG NC possessed significant interfacial active sites, thereby greatly enhancing its performance for hydrogen uptake and release. The influence of the applied electrode potential on the formation of α-phase and β-phase nucleation in the as-synthesized materials was further investigated. The concepts and strategies discussed in this study contribute new avenues toward future carbon-based material designs for a sustainable hydrogen economy and energy applications.