Abstract
It has been extremely difficult for conventional computational approaches to reliably predict the properties of multi-reference systems (i.e., systems possessing radical character) at the nanoscale. To resolve this, we employ thermally-assisted-occupation density functional theory (TAO-DFT) to predict the electronic and hydrogen storage properties of Li-terminated linear boron chains (Li2Bn), with n boron atoms (n = 6, 8, …, and 16). From our TAO-DFT results, Li2Bn, which possess radical character, can bind up to 4 H2 molecules per Li, with the binding energies in the desirable regime (between 20 and 40 kJ/mol per H2). The hydrogen gravimetric storage capacities of Li2Bn range from 7.9 to 17.0 wt%, achieving the ultimate goal of the United States Department of Energy. Accordingly, Li2Bn could be promising media for storing and releasing H2 at temperatures much higher than the boiling point of liquid nitrogen.
Highlights
Metal-organic frameworks (MOFs) and metal hydrides are adopted for storing hydrogen
In our previous thermally-assisted-occupation density functional theory (TAO-DFT) studies, Li-adsorbed acenes[55] and Li-terminated linear carbon chains (Li2Cn)[57] were found to be promising hydrogen storage material (HSM) at near-ambient conditions, showing that the search for promising HSMs can be extended to large systems possessing radical character
Since Li2Bn (n = 6, 8, ..., and 16) is able to adsorb a total of 8 H2 molecules (i.e., 4 per Li), where both the average hydrogen binding energies and successive hydrogen binding energies are in the aforementioned desirable regime, we calculate the respective hydrogen gravimetric storage capacity using[57]
Summary
It has been extremely difficult for conventional computational approaches to reliably predict the properties of multi-reference systems (i.e., systems possessing radical character) at the nanoscale. We employ thermally-assisted-occupation density functional theory (TAO-DFT) to predict the electronic and hydrogen storage properties of Li-terminated linear boron chains (Li2Bn), with n boron atoms (n = 6, 8, ..., and 16). Li-modified boron nanomaterials can potentially be HSMs. Among boron materials, there has recently been considerable interest in linear boron chains (Bn), containing n boron atoms bonded with sp[1] hybridization (see Fig. 1(a)), because of their promising electronic and mechanochemical properties. In our previous TAO-DFT studies, Li-adsorbed acenes[55] and Li-terminated linear carbon chains (Li2Cn)[57] were found to be promising HSMs at near-ambient conditions, showing that the search for promising HSMs can be extended to large systems possessing radical character.
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