Hydrogen Adsorption and Isotope Mixing on Copper-Functionalized Activated Carbons

High-specific surface area (SSA) carbons were functionalized with copper nanoclusters and evaluated as potential hydrogen storage materials. The adsorption and desorption behaviors of the copper-functionalized material and pristine high-SSA carbon are compared between 77 and 400 K using adsorption isotherms up to 10 MPa and by temperature-programmed desorption of isotopic hydrogen. The high-SSA activated carbon with copper nanoclusters exhibited two desorption behaviors. (1) A desorption peak at 120 K, which was associated with physisorption on carbon, and (2) a desorption peak at 310 K, which was associated with a chemisorption process involving copper. The desorption from copper was strongly dependent on the hydrogen pressure used for loading, and dissociation of the hydrogen could be avoided by loading at low temperature and pressure. An enhancement of hydrogen uptake in the low-coverage (Henry's law) regime at ambient temperatures with copper nanoclusters was observed, demonstrating an increased adsorption enthalpy with the copper-modified material. Binding site energies of 6 and 20 kJ/mol for H2 physisorption and H chemisorption, respectively, were obtained from fits to isotherms.