Ferroelectric polarization-controlled hydrogen storage in heteroatom-functionalized graphene/In₂Se₃ heterostructures

Hydrogen storage remains a key challenge for advancing clean energy technologies, requiring materials with high capacity and reversible adsorption. Here, density functional theory (DFT) calculations are employed to investigate heteroatom-decorated single-vacancy graphene (SVG) and its ferroelectric (FE) In₂Se₃ heterostructures (HSs) as potential hydrogen storage media. The constructed SVG/In₂Se₃ HSs integrate the high capability of single-atom active sites with the switchable polarization of the FE substrate, establishing an effective platform for tunable hydrogen adsorption. Among these configurations, the Ca-SVG/In₂Se₃ HSs exhibit the most favourable hydrogen-storage behaviour. The downward ferroelectric polarization strengthens the Kubas-type interaction (0.2-0.6 eV), enabling the accommodation of up to seven H₂ molecules, while the upward polarization significantly weakens this interaction and thus promotes facile release. Notably, the reversible polarization switching provides a low-energy pathway for H₂ desorption, offering an electric-field-controlled alternative to thermal release. Furthermore, the electronegativity-to-radius ratio (χ/r) is proposed as a robust pre-screening descriptor, exhibiting a strong correlation with C-M bond lengths and hydrogen adsorption behaviour, thereby identifying χ/r as an effective criterion for rational material selection. Charge transfer at the active sites subsequently serves as the primary descriptor for evaluating hydrogen adsorption, with this process being significantly modulated by ferroelectric polarization. These findings demonstrate a polarization-regulated hydrogen storage mechanism enabled by the rational construction of ferroelectric HSs and offering fundamental insights for the design of next-generation energy storage materials.