Hydrogen storage on nanoporous carbons

Sustainable hydrogen (e.g., produced from biomass) is of much current interest as an energy store and/or carrier. Attractions are that H2 generates .apprx.143 MJ kg-1 when it reacts with O2, with only H2O as the product. This compares to fossil fuels, which generate 10-50 MJ kg-1, plus environmentally-damaging CO2. However, there are many challenges to be met before energy systems based on H2 are tech. feasible or socially/economically acceptable. One of the main challenges is to store H2 safely, effectively and at low-cost. This paper presents the results of a mainly exptl. study of H2 sorption in nanoporous carbons. This is part of a broad examn. of the potential of these materials as storage media for H2 in low vol. and low mass energy systems, in comparison with other storage media such as light metal hydrides, and with liq. and high-pressure gas storage. Note that the new term nanoporous refers to pores in the size range 0.1 to 100 nm. We have measured kinetic and equil. H2 sorption isotherms on a wide range of carbons for temps. in the range 77 to 298 K and for pressures in the range 0 to 20 bar using a gravimetric system. Initial conclusions are that reasonable amts. of H2 (up to 5 wt.%) are adsorbed at 77 K on many different carbons, but that amts. adsorbed at 298 K are at least an order of magnitude lower. There is some evidence that at 77 K adsorption is not fully equilibrated even over periods of many hours at a given pressure, and comprises an irreversible component (i.e., there is some desorption hysteresis) possibly arising from impurities in the H2 used in expts. [on SciFinder (R)]