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

Abstract

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.