Modeling of low temperature adsorption of hydrogen in carbon nanopores

International audienceHydrogen is very likely the ultimate future of the energetic economy of the world: it is ubiquitous in the environment, it can be sustainably produced, and it holds the highest energy per unit mass of any fuel (except nuclear). If combusted, it produces only water. Therefore hydrogen, when used as energy vector, enters the natural water cycle of the Earth, with no impact on the planet’s climate. Today the major issue of the widespread hydrogen use is its low mass and low volume storage, as the energy density of hydrogen gas is low. Physisorption in nanoporous materials seems to be the most promising way of storage, as it does not release much energy during adsorption and in principle do not require the energy input when hydrogen is released. In this paper we will present the Grand Canonical Monte Carlo simulations of hydrogen adsorption in slit-shape carbon nanopores. Our calculations confirm the very controversial experimental results [1-3] showing that under confinement the density of hydrogen film adsorbed on the carbon wall exceeds that of the bulk liquid at low temperature and approaches that of solid hydrogen at extreme pressures. The densification of hydrogen is restricted to the layer in direct contact with the adsorbent, and does not depend significantly on the pore size (at least for the pores of the width from 0.6 to 3.0 nm) nor on the temperature (for 50 K< T < 180 K).The simulations are confronted with the experimental isotherms of hydrogen adsorption in KOH - activated nanoporous carbons [3] obtained from biomass waste [4]. The numerical and experimental results are coherent and prove that the interaction between hydrogen molecules and carbon surface is strong enough to produce adsorbed layer with solid hydrogen density