Calcium-Decorated Polygon-Graphenes for Hydrogen Storage

We performed first-principles calculations to investigate hydrogen (H-2) storage properties of bare and calcium (Ca)-decorated polygon-graphenes, i.e., biphenylene and psi-graphene monolayers consisting of polygons, from tetragons to octagons. In pristine forms, both biphenylene and psi-graphene bind H-2 weakly. However, upon Ca doping, biphenylene adsorbed up to five H-2 molecules regardless of polygonal sites, whereas psi-graphene anchored up to six and five H-2 molecules to pentagonal and heptagonal sites, respectively. In all the cases, the H-2 binding energy was similar to 0.30 eV, enabling reversible room-temperature H-2 storage. The H-2 storage capacity can reach similar to 6.8 and similar to 4.2 wt % for Ca-decorated biphenylene and psi-graphene, respectively. Using equilibrium thermodynamics, we showed the adsorption and desorption of H-2 at 300 and 380 K under ambient pressure, respectively. This clearly indicates that Ca-decorated 2D sp(2) carbon sheets with polygons (biphenylene, psi-graphene) could be used as promising H-2 storage materials.

Automated summary

We used first-principles calculations to study the hydrogen storage properties of bare and calcium-decorated polygon-graphenes. Both biphenylene and psi-graphene bind H-2 weakly in their pristine forms, but upon Ca doping, they can adsorb multiple H-2 molecules. The H-2 binding energy is around 0.30 eV, enabling reversible room-temperature storage with a capacity of up to 6.8 and 4.2 wt% for Ca-decorated biphenylene and psi-graphene respectively. These findings highlight the potential of Ca-decorated 2D carbon sheets as promising H-2 storage materials.