Enhancing energy storage efficiency of lithiated carbon nitride (C7N6) monolayers under co-adsorption of H2 and CH4

There is a great interest in the design of innovative concepts and strategies of nitrogen rich carboneous materials for exploring their hydrogen (H₂) storage properties. Methane (CH₄) storage can be an alternative to H₂ because the combustion energy of the former is around three times higher than the latter. However, strong inter-molecular repulsion between the CH₄ molecules is a major bottleneck to achieve a high gravimetric density. In this study, we use first principles density functional calculations to investigate the coadoption of H₂ and CH₄ on Li decorated carbon nitride (Li-C₇N₆) monolayer. The repulsion between CH₄ molecules has been avoided by keeping them in asymmetric configuration whereas the repulsion between CH₄-H₂ is in moderation due to the exploitation of open Li doped sites on C₇N₆ surface. Though Li-C₇N₆ has a lower H₂ or CH₄ storage capacity due to weak van der Waals interactions, the capacity could be doubled with a novel strategy of co-mixing of H₂ with CH₄ which results into a significantly high gravimetric density of 8.1 wt%. This clearly shows that the CH₄-H₂ co-mixing strategies have the potential to further propel the prospects of C₇N₆ monolayers for reversible clean energy storage applications.