Critical Review of H/Carbon Literature and Ab Initio Research for a Chemical Site between Two Coronenes

A survey of the recent literature on adsorption shows that H2 storage in the porosity of carbon solids is an active field of research. The results over 15 experimental studies show results ranging from 1.5 to 67% (in mass) of H2 storage, near normal conditions of temperature and pressure. Common sense and theoretical works evidenced that the large value of storing capacity cannot be accounted from physisorption and capillary condensation so far up from the bulk H2 critical temperature. Many of the experimental results show rather small storing ability of hydrogen (less than the US Department of Energy requirement: 6.5 %) Some parameters of the problem may not have been correctly controlled. Indeed, four different research teams notice that — of the H2 introduced under pressure remains actually for 24 hours or needs a 100°C heating to remove. After a critical review of literature, we came to the conclusion that some parameters are not well understood. We started an ab initio study aiming at finding the conditions for weak chemisorption of H2 or H° confined between two coronenes molecules: we compute the 0 K ab initio adsorption potential energy for H2 and H° between two coronene molecules as a function of the intercoronene distance. We demonstrate that H2 can only physisorb (with a potential well of 49 meV at 7.5 A taking into account dispersion interactions) and that H° is able to chemically bridge two superimposed C-p orbitals.