Ultrahigh hydrogen storage capacity of B3O3 monolayer with electric-field-controlled reversible dehydrogenation

Abstract

State-of-the-art density functional theory (DFT) calculations were employed to investigate the potential of the newly synthesized porous B₃O₃ monolayer (ML) for hydrogen storage applications. While pristine B₃O₃ ML exhibits weak hydrogen adsorption ($E_{ads}\cong 0.12$ eV per H₂ molecule), its decoration with lithium (Li) or sodium (Na) can significantly enhance the average adsorption energy ($E_{ads}\cong 0.32$ eV per H₂ molecule). The pore of B₃O₃ has more capacity towards Li doping, with the ability to accommodate up to six Li atoms, each capable of attracting more than three H₂ molecules, compared to a maximum of only two Na atoms. Ab-initio molecular dynamics (AIMD) simulations confirm the thermodynamic stability of both 6Li@B₃O₃ and 2Na@B₃O₃ MLs at room temperature (RT $\sim$ 300 K). Thermodynamic analysis, based on Langmuir model, showed that the 6Li@B₃O₃ primitive cell can store approximately 19.26 H₂ molecules, yielding a high effective gravimetric capacity ($C_{eff}\cong$ 16.09 wt% at RT), whereas 2Na@ B₃O₃ can store about 11.58 H₂ molecules only ($C_{eff}\cong$ 10.07 wt% at RT). Both values are significantly higher than the U.S. Department of Energy's 2025 target of 5.5 wt%. Furthermore, charge transfer analysis based on the Bader method and charge density difference (CDD) has confirmed charge transfer from Li/Na atoms to H₂ molecules, confirming the role of H₂ as charge acceptors. The application of electric fields oriented away from the surface can reduce the adsorption energy, thereby facilitating H₂ desorption. Based on these characteristics, Li- and Na-decorated B₃O₃ ML stand out as promising candidate materials for hydrogen storage applications.