Enhancing energy storage efficiency of lithiated carbon nitride (C7N6) monolayers under co-adsorption of H-2 and CH4

There is a great interest in the design of innovative concepts and strategies of nitrogen rich carboneous materials for exploring their hydrogen (H-2) storage properties. Methane (CH4) storage can be an alternative to H-2 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 H-2 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-H-2 is in moderation due to the exploitation of open Li doped sites on C7N6 surface. Though Li-C7N6 has a lower H-2 or CH4 storage capacity due to weak van der Waals interactions, the capacity could be doubled with a novel strategy of co-mixing of H-2 with CH4 which results into a significantly high gravimetric density of 8.1 wt%. This clearly shows that the CH4-H-2 co-mixing strategies have the potential to further propel the prospects of C7N6 monolayers for reversible clean energy storage applications.