Hydrogen storage by spillover on graphene as a phase nucleation process

Hydrogen chemisorption on graphene receptor-substrate is of great interest for energy storage. However, it is difficult to reconcile with a single H atom binding to carbon being weaker than it is within initial molecular ${\text{H}}_{2}$. This paradox is resolved by presenting the process as phase nucleation in the reaction ${\text{Rec}}^{\text{solid}}+{\text{H}}_{2}^{\text{gas}}\ensuremath{\leftrightarrow}{(\text{H}\ensuremath{\cdot}\text{Rec})}^{\text{solid}}$, with the nucleus' energy separable into the Gibbs formation potential and the interface part. Atomistic calculations bridge remarkably with the macroscopic-continuum description and show a feasible path to $7.7\text{ }\text{wt}\text{ }%$ H content at nearly ambient conditions.