Hydrogen Storage Properties of Vanadium-Decorated Holey Graphyne: A Density Functional Theory Study

Abstract

Hydrogen storage remains a key challenge for the practical deployment of hydrogen-based energy systems due to the limited storage capacity and weak hydrogen binding in conventional carbon-based and metal-decorated materials. Using density functional theory (DFT), we have investigated the hydrogen storage characteristics of vanadium-decorated holey graphyne (HGY), which is a recently synthesized form of carbon. Holey graphyne (HGY) possesses intrinsic nanopores and uniformly distributed carbon rings, providing many more anchoring sites for metal atoms and superior hydrogen adsorption compared with traditional carbon materials. Vanadium is selected as the decorating metal due to its favorable d-orbital characteristics, moderate atomic weight, and strong binding to carbon frameworks without clustering. The V atom strongly binds to the HGY sheet with a binding energy equal to −3.25 eV. Each V atom doped on the HGY sheet is capable of adsorbing up to five H₂ molecules. The average H₂ adsorption energy is coming out to be −0.62 eV/H₂. Impressively, the gravimetric hydrogen storage capacity reaches 6.43 wt%, exceeding the US Department of Energy target. Compared to previously reported carbon-based and metal-decorated nanomaterials, the V-doped HGY system exhibits a superior balance of storage capacity, adsorption energy, and thermal stability. Bader charge analysis reveals that the V atom experienced a loss of 0.109e⁻. The hydrogen molecules bond with the V atoms through Kubas interactions, which involve charge donation and back-donation between the metal d-orbital and the H s-orbital. Molecular dynamics simulations based on ab initio methods verify the structural integrity of the V-decorated HGY system at room temperature. The stability of the system at room temperature, the sufficient diffusion energy barrier that prevents metal–metal clustering, the high gravimetric hydrogen uptake, and appropriate adsorption energy all point to V-doped HGY as a very promising material for devices with high-capacity hydrogen storage.