Enhanced Methane Storage in Graphene Oxide Induced by an External Electric Field: A Study by MD Simulations and DFT Calculation.

To improve the methane (CH) storage performance of graphene oxide (GO), molecular dynamics (MD) simulations and density functional theory (DFT) calculation were employed to investigate the effect of electric field (EF) on the adsorption and desorption performances of monolayer graphene modified with three oxygen-containing functional groups (hydroxyl, carboxyl, and epoxy) as the CH storage material. Through the calculation and analysis of the radial distribution function (RDF), adsorption energy, adsorption weight percentage, and the amount of CH released, the mechanisms of influence on adsorption and desorption performances caused by an external EF were revealed. The study results showed that the external EF can significantly enhance the adsorption energy of CH on hydroxylated graphene (GO-OH) and carboxylated graphene (GO-COOH), making it easier to adsorb CH, and improve the adsorption capacity. Whereas the EF severely weakened the adsorption energy of CH on epoxy-modified graphene (GO-COC) and reduced the adsorption capacity of GO-COC. For the desorption process, applying the EF can decrease the CH release of GO-OH and GO-COOH but increase the CH release of GO-COC. To sum up, when an EF is present, the adsorption properties of -COOH and -OH and desorption properties of -COC will be improved, but the desorption properties of -COOH and -OH and the adsorption properties of -COC will be weakened. The findings in this study are expected to propose a novel non-chemical method to improve the storage capacity of GO for CH.