Two-dimensional B7P2: Dual-purpose functional material for hydrogen evolution reaction/hydrogen storage

Abstract

It is well known that the development of dual-purpose materials is more significant and valuable than single-use materials due to the diversity of their use purposes. Based on density functional theory (DFT), the hydrogen evolution/hydrogen storage characteristics of two-dimensional (2D) B7P2 monolayer are systematically studied in this paper, focusing on the key word of clean energy-“hydrogen”. The results show that the B7P2 monolayer can be used as a stable metal-free decorated catalyst for hydrogen evolution reaction (HER), which is renewable and environmentally friendly. The calculated Gibbs free energy (ΔGH∗) is 0.06 eV, which is comparable or even better than that of Pt catalyst (ΔGH∗ = −0.09 eV). In addition, we also found that the increase of hydrogen coverage and strain driving (−2%–2%) did not further enhance the HER activity of B7P2 monolayer, showing a poor ΔGH∗. In the aspect of hydrogen storage, we have investigated the hydrogen storage performances of alkali-metal (Li, Na and K) doped B7P2. It is found that in the fully loaded case, B7P2Li6 is a promising hydrogen storage material with a 7.5 wt% H2 content and 0.15 eV/H2 average hydrogen adsorption energy (Eave). Moreover, ab initio molecular dynamics (AIMD) calculations show that there is no dynamic barrier for H2 desorption of Li-decorated B7P2 monolayer. In conclusion, our results indicate that the B7P2 monolayer is not only an excellent catalyst for HER, but also a promising hydrogen storage medium.