Calcium-Decorated Polygon-Graphenes for Hydrogen Storage

Abstract

We performed first-principles calculations to investigate hydrogen (H2) storage properties of bare and calcium (Ca)-decorated polygon-graphenes, i.e., biphenylene and ψ-graphene monolayers consisting of polygons, from tetragons to octagons. In pristine forms, both biphenylene and ψ-graphene bind H2 weakly. However, upon Ca doping, biphenylene adsorbed up to five H2 molecules regardless of polygonal sites, whereas ψ-graphene anchored up to six and five H2 molecules to pentagonal and heptagonal sites, respectively. In all the cases, the H2 binding energy was ∼0.30 eV, enabling reversible room-temperature H2 storage. The H2 storage capacity can reach ∼6.8 and ∼4.2 wt % for Ca-decorated biphenylene and ψ-graphene, respectively. Using equilibrium thermodynamics, we showed the adsorption and desorption of H2 at 300 and 380 K under ambient pressure, respectively. This clearly indicates that Ca-decorated 2D sp2 carbon sheets with polygons (biphenylene, ψ-graphene) could be used as promising H2 storage materials.

Reversible Hydrogen Storage in a Superalkali NLi4-Decorated Biphenylene Monolayer: Insights from a First-Principles Study

“…Two-dimensional (2D) materials have gained attention in storage applications owing to their exceptionally unique characteristics, such as their high surface area, lightweight nature, and multiple active sites, which make them highly promising for hydrogen storage. − In the pristine state, most 2D materials exhibit hydrogen binding through weak physisorption, leading to reduced capacities for hydrogen storage and restricting their functionality to low temperatures, rendering them unsuitable for practical applications. , Consequently, to enable effective storage and release under achievable storage conditions, there is a need to enhance the binding between 2D material and hydrogen, i.e., the H 2 adsorption energies onto the host material. , One approach to enhance the binding involves the functionalization of materials with metal, including alkali or alkaline metals as well as transition metals. − Influenced by this notion, multiple other studies have demonstrated increased H 2 storage as a result of such modifications. For instance, Nair et al conducted experimental investigations into effective hydrogen storage using Pd-decorated g-C 3 N 4 , revealing a gravimetric density of 2.6 wt % .…”

“…These unique characteristics render it appropriate for diverse applications, such as chemical catalysis, battery application, and hydrogen storage . Earlier studies have investigated the hydrogen storage potential of alkali metals (as Li, Ca, and K) , and transition metals (as Sc, Zr, and V) , -decorated BPN. Denis et al reported the hydrogen weight percentage of Li-decorated BPN as 7.4 wt % and the average adsorption energy as 0.20 eV .…”