Title : Theory of reversible hydrogen storage in metal decorated 2D nanomaterials beyond graphene
Abstract:
By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of alkali metal (AM), alkali-earth metal (AEM), and transition metal (TM) decorated single-layer carbon nanomaterials, including, holey-graphyne (HGY) and biphenylene sheet (BPS). We have observed that one unit cell of HGY can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5 H2 molecules with an average binding energy and average desorption temperature of -0.36 eV/H2 and 464 K, respectively [1]. The gravimetric weight percentage of hydrogen is 9.80 %, which is considerably higher than the Department of Energy, United-States (DOE-US) requirements of 6.5 %. BPS is a recently synthesized advanced 2D carbon allotrope with four, six, and eight-membered carbon rings. We have kept various alkali and alkali-earth metals, including Na, Be, Mg, K, Ca, at different sites of BPS and found that K and Ca atoms prefer to bind individually on the BPS instead of forming clusters. It was found that 2?2?1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5 H2, leading to 11.90 % or 11.63 % of hydrogen uptake, respectively, which is significantly higher than the DOE-US requirements [2]. The average adsorption energy of H2 for K and Ca decorated BPS is -0.24 eV and -0.33 eV, respectively, in the suitable range for reversible H2 storage. Hydrogen molecules get polarized in the vicinity of ionized metal atoms, and get attached to the metal atoms through electrostatic and van der Waals interactions. We have found that Kubas interactions also play a significant role in hydrogen binding with Ca and Sc atom. We have estimated the desorption temperatures of H2 and found that the adsorbed H2 can be utilized for reversible use. We have found that sufficient energy barriers exist for the movement of metal atoms that can prevent clustering, calculated using the climbing-image nudged elastic band (CI-NEB) method. The solidity of metal decorated HGY and BPS structures were investigated using AIMD simulations.
[1] V. Mahamiya, A. Shukla, N. Garg, and B. Chakraborty, High-Capacity Reversible Hydrogen Storage in Scandium Decorated Holey Graphyne: Theoretical Perspectives, Int. J. Hydrogen Energy 47, 7870 (2022).
[2] V. Mahamiya, A. Shukla, and B. Chakraborty, Ultrahigh Reversible Hydrogen Storage in K and Ca Decorated 4-6-8 Biphenylene Sheet, Int. J. Hydrogen Energy 1 (2022).
Audience Take Away:
- Hydrogen is considered one of the most suitable alternatives to fossil fuels in present times because it is highly abundant, possess high energy density, and does not produce harmful pollutant during combustion.
- In this talk, I will describe the theoretical methodology for hydrogen storage in solid state form.
- I will also discuss the theory behind the adsorption of hydrogen molecules on 2D nanomaterials and the practical difficulties associated with it.
- I believe that the audience will get familiar with the hydrogen storage problem and computational modeling, which will motivate them to design novel materials for hydrogen storage applications.
