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Hydrogen Storage on Platinum Nanoparticles Doped on Superactivated Carbon

2007; American Chemical Society; Volume: 111; Issue: 29 Linguagem: Inglês

10.1021/jp072867q

1932-7455

Yingwei Li, Ralph T. Yang,

Catalytic Processes in Materials Science

The equilibrium and kinetics of hydrogen storage on Pt nanoparticles doped on AX-21 superactivated carbon were studied. The Pt/AX-21 sample was prepared by ultrasound-assisted impregnation of H2PtCl6 in a solution of acetone. The dispersion of platinum was determined by CO/H2 chemisorption and high-resolution transmission electron microscopy (HRTEM). Hydrogen adsorption isotherms and kinetics were measured at 298−348 K and up to 10 MPa. HRTEM images showed that Pt was well dispersed with a uniform particle size ∼2 nm. CO chemisorption results indicated that the dispersion was 58%. By doping 5.6 wt % Pt, the hydrogen storage capacity of AX-21 was enhanced to 1.2 wt % at 298 K and 10 MPa. Furthermore, the isotherm was totally reversible and rechargeable at 298 K. The overall isosteric heats of adsorption (−23 to −15 kJ/mol) and the apparent activation energy for surface diffusion (7.6 kJ/mol) were determined from the temperature dependence of, respectively, equilibrium isotherm and diffusion time constant. Diffusion of the spiltover H atoms on carbon surface at room temperature was a slow process, which resulted in slow hydrogen uptake and desorption rates especially at higher pressures (higher surface concentrations). Desorption appeared to follow a reverse spillover process. The simple mechanistic model that we reported previously was capable of interpreting all experimental data in this study.