Superalkali NLi4 anchored on BN sheets for reversible hydrogen storage

Abstract

Developing an efficient storage medium is a substantial challenge for the utilization of hydrogen as an energy carrier, and designing materials with intermediate holding strength for hydrogen is the key to the solution. In this paper, we decorate h-BN using superalkali NLi4 and investigate the hydrogen storage properties by density functional theory. NLi4 clusters can be anchored stably on BN sheets with a binding energy −1.43\u2009eV. As the NLi4 species has enhanced stability, decoration using the superalkali effectively improves the aggregation of the metal atoms on a substrate. Replacing alkali metal atoms by superalkalis also offers more spaces for H2 adsorption. The H2 molecules adsorbed on the bottom Li+ cations are strongly polarized due to the small radius of Li+, and the H2 molecules attached to the top Li+ are adsorbed by feeding back the excess electron up to the antibonding σ* orbitals of the H2 molecules. Each NLi4 can absorb nine H2 molecules with adsorption energies about −0.20\u2009eV/H2. The adsorption strengths fall in the ideal window for reversible uptake-release at ambient temperatures. The hydrogen storage capacity at the decoration density of NLi4/BN\u2009=\u20091:6 reaches 9.40\u2009wt.\u2009%. The present study suggests that NLi4 decorated 2D materials can be potential candidates for hydrogen storage at room temperature.