Reversible hydrogen storage tendency of light-metal (Li/Na/K) decorated carbon nitride (C9N4) monolayer

Abstract

The emergence of hydrogen (H2) as a future carrier of energy and the issue related to its storage leads to the exploration of two-dimensional materials, which have the potential to be explored as H2 storage materials. In this regard, potential of alkali metals (Li/Na/K) decorated two-dimensional carbon-nitride (C9N4) monolayer is studied for H2 storage by performing first-principles density functional theory (DFT) computations. Metal dopants, Li, Na, and K show strong binding interactions with the C9N4 due to the transfer of charges from the formers to the later. In addition to strong bindings with C9N4 high diffusion barriers further nullify the cluster formation among metal dopants. The effect of temperature on the stability of alkali metal decorated C9N4 is studied in terms of ab-initio molecular dynamics (AIMD) simulations. The effect of metal decoration on electronic as well as magnetic properties of C9N4 are studied in terms of partial density of states (PDOS) plots. We find that each Li of Li-doped C9N4 (Li@C9N4) can stably binds six H2 molecules without disintegration and results in the average adsorption energy of −0.20 eV, leading to a notably high H2 storage capability of 11.9 wt%. Similarly, the storage capacities and average H2 adsorption energies in the case of Na@C9N4 and K@C9N4 complexes fulfil the US Department of Energy (DOE) criteria. The electronic, AIMD, and thermodynamics analysis in this study provide an insight into that alkali metal decorated C9N4 as reversible H2 storage material.