Ultrahigh reversible hydrogen storage in K and Ca decorated 4-6-8 biphenylene sheet

TL;DR

This study predicts that K and Ca decorated biphenylene sheets can store hydrogen at capacities exceeding DOE standards, with reversible adsorption energies and stable structures suitable for practical hydrogen storage applications.

Contribution

The paper introduces a novel prediction of ultrahigh reversible hydrogen storage in K and Ca decorated biphenylene sheets using DFT and AIMD simulations, highlighting their stability and capacity.

Findings

Hydrogen storage capacity exceeds 11%, surpassing DOE standards.

K and Ca atoms prefer to bind individually, avoiding clustering.

Hydrogen adsorption energies are within the reversible range.

Abstract

By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of K and Ca decorated single-layer biphenylene sheet (BPS). 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 2x2x1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5 H$_2$, leading to 11.90 % or 11.63 % of hydrogen uptake, respectively, which is significantly higher than the DOE-US demands of 6.5 %. The average adsorption energy of H$_2$ for K and Ca decorated BPS is -0.24 eV and -0.33 eV, respectively, in the suitable range for reversible H$_2$ storage. Hydrogen molecules get polarized in the vicinity of ionized metal atoms hence get attached to the metal atoms through electrostatic and van der Waals interactions. We have estimated the desorption temperatures of H$_2$ and found that the adsorbed H$_2$ can be utilized for reversible use. We have found that a sufficient energy barrier of 2.52 eV exists for the movement of Ca atoms, calculated using the climbing-image nudged elastic band (CI-NEB) method. This energy barrier can prevent the clustering issue of Ca atoms. The solidity of K and Ca decorated BPS structures were investigated using AIMD simulations.