Potentially reversible hydrogen storage medium: Calcium-decorated boron-doped blue phosphorene

Abstract

Developing novel hydrogen storage materials with high capacity and efficient reversibility at ambient conditions is crucial to the extensive use of hydrogen energy. In this study, we have systematically investigated the hydrogen storage performances of Ca-decorated boron-doped blue phosphorene (B@BlueP) monolayers by using first-principles calculations. The results show that substitutional boron doping can enhance the interaction between the Ca atom and BlueP and effectively hinder the formation of Ca clusters on the surface of BlueP. The Ca-decorated B@BlueP can store six hydrogen molecules per Ca atom with average adsorption energies of around 0.17–0.24 eV/H2. Electronic structure analysis confirms that both the polarization of hydrogen molecules under the local electrostatic field and the hybridization of Ca-s/d orbitals with H2-σ orbitals contribute to the adsorption of hydrogen molecules in the surrounding of the Ca atom. The decoration of double-sided Ca atoms can lead to a high theoretical gravimetric hydrogen density of 7.29–7.76 wt%, exceeding the storage goal of 5.50 wt% proposed by US-DOE for applications. Furthermore, the practical hydrogen storage capacity at different pressures and temperatures was also studied through thermodynamic analysis, and the storage capacity is calculated to be around 5.50 wt% in practical circumstances (298 K/30 atm and 358 K/5 atm are used as adsorption and desorption conditions, respectively). Hence, the Ca-decorated B@BlueP monolayers have promising potential as reversible hydrogen storage materials under ambient conditions.