High-Performance Pd-Based Hydrogen Spillover Catalysts for Hydrogen Storage

High surface area carbon materials are promising for low-temperature storage of hydrogen by physisorption. To achieve acceptable hydrogen capacities at ambient temperature, chemisorption must come into play. The dispersion of transition metal catalysts to carbon materials can enhance the ambient temperature adsorption capacity of the carbon materials via the hydrogen spillover mechanism. In this study, three different hydrogen dissociation catalysts (Pd, PdAg, and PdCd nanoparticles) were dispersed onto surfaces of activated carbon. The surface composition of these metal-dispersed carbon materials was analyzed using X-ray photoelectron spectroscopy (XPS) and the specific surface areas, and pore sizes were measured using N-2 adsorption/desorption. The effect of the dispersed catalysts on the hydrogen adsorption properties of the activated carbon was systemically investigated at 77 K and room temperature (295 K) using a volumetric gas adsorption technique. At 77 K, the catalysts have no effect, and the hydrogen capacity of the materials is strictly related to the specific surface area. At room temperature, hydrogen spillover was observed from the catalysts to the carbon material. The hydrogen capacity is related to the adsorption strength of hydrogen atoms to the catalyst particle surface atoms, which was verified with DFT calculations. In addition, this study reveals that the PdCd nanoparticle possesses much higher hydrogen spillover enhancement (108%) than the pure Pd and PdAg nanoparticles, promising for hydrogen storage.