Is Hydrogen Storage Possible in Metal-Doped Graphite 2D Systems in Conditions Found on Earth?

Density functional theory (DFT) calculations are performed for the adsorption energy of hydrogen and oxygen on graphene decorated with a wide set of metals (Li, Na, K, Al, Ti, V, Ni, Cu, Pd, Pt). It is found that oxygen interferes with hydrogen adsorption by either blocking the adsorption site or by the irreversible oxidation of the metal decoration. The most promising decorations are Ni, Pd, and Pt due to a reasonable relationship of adsorption energies which minimize the oxygen interference. The DFT results are used to parametrize a statistical mechanical model which allows evaluation of the effect of partial pressures in the gas phase during storage. According to this model, even in the most promising case, it is necessary to reduce the oxygen partial pressure close to ultrahigh vacuum conditions to allow hydrogen storage.

Figure 1

Left: Hydrogen coverage degree ${\theta }_{{\mathrm{H}}_2}$ as a function of the oxygen partial pressure $p_{{\mathrm{O}}_2}$ for the best suited hydrogen storage systems: Pt-graphene (left), Pd-graphene (center), and Ni-graphene (right). The partial hydrogen pressure representing the hydrogen supply was $p_{{\mathrm{H}}_2}=1\mathrm{bar}$ (blue curve) and $p_{{\mathrm{H}}_2}=200\mathrm{bar}$ (red curve). The inset shows the situation corresponding to ${\theta }_{{\mathrm{H}}_2}=0.5$. Hydrogen coverage was calculated using Eq. (7), with ${\theta }_{{\mathrm{H}}_2}=\frac{{\overline{s}}_{{\mathrm{H}}_2}}{2}$.