High hydrogen storage capacity and reversible storage/release mechanism of the BC2N monolayers via charge modulation

Although hydrogen is an effective alternative energy source to fossil fuels, its storage is a challenge for extensive applications. The hydrogen storage performance and mechanism of the BC2N monolayers with and without modulation of strain and charge were investigated using first-principles methods. The pure BC2N monolayer achieves a high hydrogen storage gravimetric density (HSGD) of 10.95 wt. %; however, the average adsorption energy (Ead) of H2 molecules is only 0.138 eV, which immensely hinders its practical applications and motivates us to introduce clean modulations for the Ead improvement with maintaining the HSGD. Our results indicate that strain engineering has little effect on enhancing the adsorption strength of H2. However, charge engineering can efficiently modulate the interaction between H2 molecules and BC2N. When −5e charges are applied into the monolayer, Ead of H2 molecules increases to 0.225–0.460 eV. The interaction between charged BC2N and H2 molecules is of electrostatic nature. The desorption temperature of H2 molecules is between 287 and 383 K at 1 atm. The adsorption condition of 297 K∼30 atm and the desorption condition of 385 K∼1 atm for the reversible charge-modulated BC2N monolayer are preferred. Furthermore, the reversible storage/release of H2 on/from the BC2N monolayer can be easily controlled by modulating the charge states of BC2N. Combined with the analysis of desorption temperature and occupation number, our findings highlight that the BC2N monolayer with charge modulation is an ideal reversible hydrogen storage material with high HSGD and fast-kinetics.