Alloying Ratio Versus Cluster Size for Reversible Hydrogen Storage in Ni Doped Small Mg Clusters: Dispersion Corrected DFT Study

2022/02/25 by Boruah, Bishwajit, Kalita, Bulumoni
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci)

paper · doi:10.48550/arxiv.2202.12551

Abstract

Dispersion corrected density functional theory (ωB97X-D DFT) method is used to study the molecular hydrogen adsorption in Ni_nMg_m (1≥ n≥ 3,1≥ m≥9) clusters. All these clusters can effectively adsorb multiple H₂ in the preferred binding energy (BE) range between physisorption and chemisorption, i.e., 0.1 eV≥ BE ≥0.8 eV. H₂ adsorption on Ni_kMg_k (Ni:Mg=1:1), Ni_kMg_2k (Ni:Mg=1:2) and Ni_kMg_3k (Ni:Mg=1:3) (k=1-3) clusters shows fascinating behaviours in terms of Ni:Mg alloying ratio and cluster size. In each Ni:Mg ratio, the number of adsorbed H₂ in the heavier clusters (k=2, 3) becomes integral multiples of that in the lightest configuration (k=1). As a consequence, the gravimetric density of molecular hydrogen remains fixed at each Ni:Mg ratio irrespective of the cluster size. The corresponding values are 17.94 wt% (1:1), 14.46 wt% (1:2) and 13.28 wt% (1:3), which are significantly higher than the ultimate target of 6.5 wt% set by DOE, US. Molecular dynamics simulations further reveal that room temperature desorption of almost all H₂ molecules are possible for all the clusters.

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