Type-II Weyl fermion induced hydrogen adsorption in a two-dimensional electride [Ca2N]+·e−

Abstract

Electrides, in which excess electrons are weakly bounded by the lattice interstitial position, are suitable for achieving topological states. The topological properties of electrides give rise to a boost to their practical applications, e.g. catalytic field. Here, based on first-principles calculations, we discover that the two-dimensional (2D) electride [Ca₂N]⁺·e⁻ has three pairs of type-II Weyl fermions in its low-energy region, resulting in Fermi arcs at its boundary. Remarkably, the topological nature of [Ca₂N]⁺·e⁻ plays a significant role in hydrogen adsorption, which resolves the controversy over the mechanism of hydrogen adsorption in [Ca₂N]⁺·e⁻. To be specific, we can tune the adsorption energy by the number of layers, the concentrations of electrons/holes, and strain. Furthermore, we discover a positive correlation between robust type-II Weyl fermion and adsorption energy. Such a close relationship between the type-II Weyl points and adsorption energy is useful in the application of the electride [Ca₂N]⁺·e⁻, providing new insight into the study of hydrogen adsorption in electrides.