Alkali metals decorated silicon clusters (SinMn, n=6,10; M = Li, Na) as potential hydrogen storage materials: A DFT study

In this article, we have studied hydrogen storage properties of alkali-metal decorated silicon clusters (SinMn, n = 6, 10; M = Li, Na) using density functional theory (DFT). The electronic structure, stability and bonding properties of both bare and hydrogen adsorbed clusters are studied and verified using global reactivity descriptors and Quantum Theory Of Atoms in Molecules (QTAIM) study. No distortion in host clusters is observed upon adsorption. H-2 bond lengths (0.74 angstrom-0.75 angstrom), H - AM bond distances (2.134 angstrom-3.108 angstrom) and adsorption energy (0.059eV-0.141eV) confirmed the adsorption process to be molecular and physisorptive in nature. Li sites in Si6Li6 and Si10Li10 can bind up to 18H(2) and 40H(2) molecules respectively resulting in a maximum gravimetric density of 14.7 wt% and 18.7 wt% respectively. Similarly, Na sites in Si6Na6 and Si10Na10 can adsorb up to 18H(2) and 40H(2) molecules resulting in a maximum gravimetric density of 10.6 wt% and 13.6 wt% respectively. The gravimetric densities for respective clusters thus obtained are quite higher than the target 5.5 wt% as set by US-DoE. In addition to this, ADMP-MD simulation reveal that all the host clusters adsorb molecular hydrogen reversibly and can undergo room temperature (300 K) desorption. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the hydrogen storage properties of alkali-metal decorated silicon clusters using density functional theory (DFT). The results showed that the clusters can adsorb a significant amount of hydrogen, surpassing the target gravimetric density of 5.5 wt% set by US-DoE.