Superalkali functionalized two-dimensional haeckelite monolayers: A novel hydrogen storage architecture

Abstract

Exploring efficient storage mediums is the key challenge to accomplish a sustainable hydrogen economy. Material-based hydrogen (H2) storage is safe, economically viable and possesses high gravimetric density. Here, we have designed a novel H2 storage architecture by decorating graphene-like haeckelite (r57) sheets with the super-alkali (NLi4) clusters, which bonded strongly with the r57. We have performed van der Waals corrected density functional theory (DFT) calculations to study the structural, electronic, energetic, charge transfer, and H2 storage properties of one-sided (r57-NLi4) and two-sided (r57-2NLi4) coverage of r57 sheets. Exceptionally high H2 storage capacities of 10.74%, and 17.01% have been achieved for r57-NLi4, and r57-2NLi4 systems, respectively that comfortably surpass the U.S. Department of Energy's (DOE) targets. Under maximum hydrogenation, the average H2 adsorption energies have been found as 0.32 eV/H2, which is ideal for reversible H2 storage applications. We have further studied the effects of mechanical strain to explore the H2 desorption mechanism. Statistical thermodynamic analysis has been employed to study the H2 storage mechanism at varied conditions of pressures and temperatures. Our findings validate the potential of r57-xNLi4 as efficient H2 storage materials.