The hydrogen adsorption properties of commercial activated carbon (aC) samples, in particular Nuchar SA-1500, Filtercarb GCC 8x30 and Filtercarb PHA, are evaluated at different temperatures (77 K, 196 K and ambient temperature) and pressure up to 80 bar. A comprehensive characterization is carried out by means of a volumetric Sieverts-type apparatus for hydrogen adsorption measurements and helium picnometry for the skeletal density evaluation, by nitrogen adsorption measurement for the evaluation of the surface area (BET) and pore size distribution (NLDFT), by Scanning Electron Microscopy (SEM) for morphology. All the adsorption data are evaluated by Langmuir/Tóth isotherm model with a very high accuracy and the enthalpy of adsorption is calculated through the Clausius–Clapeyron equation. Comparison between the different samples is shown. The probed aC samples show interesting hydrogen storage capacity and reversible behavior up to many cycles with and without any thermal treatment in between. Our data point out the crucial role of the microporosity and ultra-microporosity in the adsorption process at low H2 pressures. The surfaces exhibit an average adsorption enthalpy around 6.5 kJ/mol while for the ultra-microporous sites a 14 kJ/mol value is found. The observed trapping behavior at 77 K is attributed to the ultra-microporous morphology of the porous structure in GCC and PHA samples. A further result is the evaluation of the hydrogen molar density in the micropores with size below 10 Å, which is 30 mmol/cm3, a value very close to the liquid hydrogen one. These results could represent an interesting starting point for a real and efficient alternative method to the hydrogen storage using cheap and easy scalable materials.
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|Titolo:||Liquid-like hydrogen in the micropores of commercial activated carbons|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||1.1 Articolo in rivista|