Sodium-Decorated SiB Monolayer for Reversible Hydrogen Storage: High-Capacity Achieved by Carbon Doping

Based on the first-principles calculation and grand canonical Monte Carlo (GCMC) simulation, the reversible hydrogen storage of Na-decorated silicon boron (SiB) and C-doped SiB monolayers have been investigated. For double side 4Na-decorated SiB monolayer, each Na atom can adsorb five H₂ molecules with the average adsorption energy of −0.18 eV/H₂, yielding an H₂ gravimetric density of 9.09 wt% and desorption temperature T_D of 227 K. To further improve the H₂ gravimetric density and desorption temperature, doping effect was employed to enhance the internal electric field between Na atom and SiB substrate. When two Si atoms in the SiB monolayer were replaced by C atoms, the adsorption energy for H₂ was significantly improved. The H₂ gravimetric density reaches to 10.63 wt% with the average adsorption energy of −0.22 eV/H₂. Meanwhile, the desorption temperature T_D was raised from 227 to 282 K, reaching the ideal condition near room temperature. In addition, the GCMC simulations further confirm that the H₂ gravimetric density can fully meet the latest hydrogen storage target (5.5 wt%) for both Na-decorated SiB monolayer and Na-decorated C-doped SiB monolayer. Our results indicate that both Na-modified SiB and C-doped SiB monolayers can be used as promising materials for reversible hydrogen storage.