Hydrogen storage in Li, Na and Ca decorated and defective borophene: a first principles study

Abstract

Recently synthesized two-dimensional (2D) borophene possesses unique structural, mechanical, electrical and optical properties. Herein, we present a comprehensive study of H 2 storage in alkali metal decorated and defect containing 2D borophene using density functional theory calculations. While the adsorption of H 2 over pristine borophene was found to be weak with a binding energy of À0.045 eV per H 2 , metal decoration and point defects enhanced the adsorption strength significantly. Interestingly, the magnitudes of binding energy for a single H 2 molecule over Li, Na and Ca decorated borophene were found to increase up to À0.36, À0.34, and À0.12 eV per H 2 , respectively. On the other hand, while the binding energy of one H 2 molecule over the borophene substrate containing a single vacancy (SV) was only À0.063 eV per H 2 , similar to that of phosphorene, the binding energy increased to an enormous À0.69 eV per H 2 over borophene containing a double vacancy (DV). To gain further insight into the H 2 adsorption process and identify sources of charge transfer, differential charge densities and projected density of states were calculated. Significant charge accumulation and depletion caused strong polarization of the H 2 molecules. Finally, Na, Li and Ca decorated borophene yielded the gravimetric densities 9.0%, 6.8%, and 7.6%, respectively. The gravimetric density of the borophene containing a DV was found to be the highest, a staggering 9.2%, owing to increased interactions between DV borophene and the H 2 molecules. These results suggest that borophene can be an effective substrate for H 2 storage by carefully engineering it with metal decoration and point defects.

Borophene and Boron‐Based Nanosheets: Recent Advances in Synthesis Strategies and Applications in the Field of Environment and Energy

“…Li, Na, and Ca‐doped defective borophene sheets (2‐ Pmmn ) were used by Halder et al. [ 115 ] to study their hydrogen storage capacity using DFT calculations. Figure 15f represents the relaxed configurations of Li, Na, and Ca decorated borophene sheets, where red, blue, and purple balls denote Li, Na, and K atoms, respectively.…”

Borophene and Boron Fullerene Materials in Hydrogen Storage: Opportunities and Challenges

“…Haldar et al also reported as imilars tudy on the H 2 storagec apacities of Li-, Na-, andC a-incorporated and defective borophene systems. [68] DFTcalculations show that alkali and alkaline earth metal decoration enhances the H 2 storage capacityo fb orophene-based systems. Borophenes hows excellent mechanical properties, with aY oung's modulus of 398 GPa nm, and exhibits Dirac transport properties and superconductivity,a sw ell as ah ydrogen gravimetric density of 7.5 wt %.…”

“…Haldar et al. also reported a similar study on the H 2 storage capacities of Li‐, Na‐, and Ca‐incorporated and defective borophene systems . DFT calculations show that alkali and alkaline earth metal decoration enhances the H 2 storage capacity of borophene‐based systems.…”

Reversible Hydrogen Storage in Metal-Decorated Honeycomb Borophene Oxide

“… 41 This approach is commonly used in other studies of H 2 storage on 2D metal-decorated substrates. 13 , 15 , 18 , 27 , 42 An inter-layer separation of more than 30 Å is used to prohibit inter-layer interactions. 19 Nevertheless, a smaller inter-layer spacing may also be applicable.…”

“… 13 , 15 − 19 Examples of such adjustments include external charge modulation, 16 , 17 and introduction of decorating atoms (mainly metals such as Li), which enhance interactions by polarizing H 2 . 13 , 18 , 19 2D boron sheets (borophene), which have been recently synthesized, 20 − 22 have shown a favorable affinity for different metal-decorating atoms, in contrast to graphene, in which clustering of metal atoms can occur. 23 , 24 Using a variety of metal decorations, such as Li, 18 , 19 , 23 Na, 25 Ca, 26 and Ti 27 on different borophene polymorphs, impressive H 2 gravimetric densities have been obtained ranging from 6 to 15 wt %, exceeding the US department of energy (DOE) requirement for onboard storage of 6.5 wt % H 2 .…”