Activated carbons doped with Pd nanoparticles for hydrogen storage

Three activated carbons (ACs) having apparent surface areas ranging from 2450 to 3200 m2/g were doped with Pd nanoparticles at different levels within the range 1.3–10.0 wt.%. Excess hydrogen storage capacities were measured at 77 and 298 K at pressures up to 8 MPa. We show that hydrogen storage at 298 K depends on Pd content at pressures up to 2–3 MPa, below which the stored amount is low (<0.2 wt.%). At higher pressures, the micropore volume controls H2 storage capacity. At 77 K, Pd doping has a negative effect on hydrogen storage whatever the pressure considered. From N2 adsorption at 77 K, TPR, XRD, TEM, and H2 chemisorption studies, we concluded that: (i) Pd particles remained mainly decorating the outer surface of the ACs; (ii) increasing Pd content produced an increase of the metal particle size; (iii) ACs with higher surface area produced smaller metallic nanoparticles at a given Pd content.