Hydrogen storage of calcium atoms adsorbed on graphene: First-principles plane wave calculations

TL;DR

This study uses first-principles calculations to demonstrate that calcium atoms adsorbed on graphene can serve as an efficient, recyclable hydrogen storage medium with high capacity, suitable for room temperature operation.

Contribution

It reveals that calcium on graphene can adsorb multiple hydrogen molecules and maintains high storage capacity, introducing a promising material for hydrogen storage.

Findings

Calcium adsorbed on graphene can store up to five H2 molecules per atom.

Hydrogen storage capacity reaches 8.4 wt % with optimized coverage.

Ca clustering is prevented by Coulomb repulsion between charged Ca atoms.

Abstract

Based on the first-principles plane wave calculations, we showed that Ca adsorbed on graphene can serve as a high-capacity hydrogen storage medium, which can be recycled by operations at room temperature. Ca is chemisorbed by donating part of its 4s-charge to the empty $\pi^*$-band of graphene. At the end adsorbed Ca atom becomes positively charged and the semi-metallic graphene change into a metallic state. While each of adsorbed Ca atoms forming the (4x4) pattern on the graphene can absorb up to five H_2 molecules, hydrogen storage capacity can be increased to 8.4 wt % by adsorbing Ca to both sides of graphene and by increasing the coverage to form the (2x2) pattern. Clustering of Ca atoms is hindered by the repulsive Coulomb interaction between charged Ca atoms.