Computational design of multilayer frameworks to achieve DOE target for on-board methane delivery

Designing new nanoporous materials with high methane delivery capacity (DC) is crucial to achieve US Department of Energy (DOE) targets of 315 v/v and 0.5 g/g for the transportation applications. We have performed extensive computational studies of methane adsorption in around 9000 multilayer frameworks (MFs) to achieve these targets. Our analysis shows that close placement of methane binding sites, optimum range of framework interaction, and pore size give rise to high methane DC in nanoporous materials. We found the highest DC of 319 v/v in general multilayer frameworks (GMFs) at 298 K. Further, we probed MFs made of graphene sheets and observed high DC of 297 v/v and 0.42 g/g in MFs with 11 and 20 A of interlayer separation, respectively. These values are close to DOE target; however, experimental realization of such MFs is difficult. Therefore, we explored methane adsorption in experimentally feasible pillared graphene frameworks (PGFs) where graphene layers are stacked with the help of suitable linker. Among the various linkers probed, PGF with cubane linker has significantly higher uptake and DC of 317 and 261 v/v, respectively. Further, we observed that in these frameworks changing adsorption and desorption temperature attains DOE target at lower pressures.