A DFT study on the promising hydrogen storage performance of a light metal atom-decorated ZnO monolayer

Abstract

The potential H2 adsorption/storage performance of the ZnO monolayer decorated with alkaline or alkaline earth metal atoms was studied using first-principle density functional theory (DFT) calculations. The light metal atom (Li, Na, K, Be, Mg, or Ca) could be atomically dispersed and decorated on the Zn–O hexatomic ring in the ZnO monolayer with high binding energy. Compared to Na-, K-, Be-, Mg-, or Ca-decorated ZnO, Li-decorated ZnO exhibited significantly stronger interactions with H2, resulting in higher adsorption energy, more transferred charges, and stronger orbital hybridizations. On the ZnO decorated with a single Li atom, four H2 molecules could be stored with an average adsorption energy of −0.242 eV. By increasing the two-sided Li coverage to one, three H2 molecules could still be stored on each decorated Li due to space limitations, with an acceptable average adsorption energy of −0.216 eV. As a result, the hydrogen storage capacity of the Li-decorated ZnO monolayer could be successfully and reasonably improved to 6.92 wt%. This study suggests that fully lithiated ZnO may have promising potential as an adsorbent for outstanding hydrogen storage performance.