Idealized Carbon-Based Materials Exhibiting Record Deliverable Capacities for Vehicular Methane Storage

Abstract

Materials for vehicular methane storage have been extensively studied, although no suitable material has been found. In this work, we use molecular simulation to investigate three types of carbon-based materials, Schwarzites, layered graphenes, and carbon nanoscrolls, for use in vehicular methane storage under adsorption conditions of 65 bar and 298 K and desorption conditions of 5.8 bar and 358 K. Ten different Schwarzites were tested and found to have high adsorption with maximums at 273 V STP /V, but middling deliverable capacities of no more than 131 V STP /V. Layered graphene and graphene nanoscrolls were found to have extremely high CH 4 adsorption capacities of 355 and 339 V STP /V, respectively, when the interlayer distance was optimized to 11 Å. The deliverable capacities of perfectly layered graphene and graphene nanoscrolls were also found to be exceptional with values of 266 and 252 V STP /V, respectively, with optimized interlayer distances. These values make idealized graphene and nanoscrolls the record holders for adsorption and deliverable capacities under vehicular methane storage conditions.

Grand Canonical Monte Carlo Simulations to Determine the Optimal Interlayer Distance of a Graphene Slit-Shaped Pore for Adsorption of Methane, Hydrogen and their Equimolar Mixture

“…This is presumably caused by the opposing graphene sheet in the 14 Å pore being closer than in the 20 Å pore and pulling the adsorption layer slightly further from the ideal position to the closest graphene sheet. The simulated molecular distribution is very similar in nature as in the simulations reported by Yu et al [64] for a 10 Å and 20 Å pore as well as the center of mass probability distributions for methane adsorbed in graphene reported by Collins et al [65]. For the mixture, all pores behave very similar as for the pure gas.…”

Evolution of the Design of CH4 Adsorbents

“…A critical property to assess materials for this application is deliverable capacity. This was assessed for carbon-based materials such as Schwarzites, layered graphenes, and nanoscrolls [154]. The materials were investigated by molecular simulations between the following temperatures and pressures: 65 bar and 298 K and 5.8 bar and 358 K. The Schwarzites did not perform very well as compared to the layered graphenes and nanoscrolls.…”

“…Structure-function relations were established for ACs [154]. ACs can be modeled as randomly oriented graphene layers.…”

Adsorbed Natural Gas Storage for Onboard Applications

“…[ 37,39 ] Specifically, MOFs ( Figure ) such as HKUST‐1, NU‐111, NU‐125, UTSA‐20, PCN‐14, Ni‐MOF‐74 (Ni‐CPO‐27), and Co(bdp) are promising for methane storage. [ 22,37,39,94,99 ] In 2014, Long and co‐workers made recommendations for the consistent reporting of methane adsorption data for MOFs: [ 46 ] i) report the background high‐pressure methane adsorption isotherms for the empty sample holder at all measured temperatures and pressures as supplementary information; [ 46,100,101 ] ii) specify whether the isotherms are reported in terms of excess, total, or absolute adsorption; [ 46,101 ] when the experimental excess adsorption data are converted to the total or absolute adsorption, the methods and assumptions should be detailed; [ 46 ] iii) when reporting volumetric uptakes, the density used and the type of density (e.g., crystallographic, [ 34 ] bulk, tap, pellet) should be given; [ 46,102 ] for instance, when crystallographic densities are used, Long and co‐workers recommended reporting details such as the unit cell volume and unit cell content; [ 42 ] iv) define the temperature and pressure before using the unit cm 3 STP ; [ 46 ] v) the method used to calculate the isosteric heats of adsorption should be detailed as well; [ 46 ] vi) in the event where mathematical fitting of experimental adsorption isotherms is performed, all fitted parameters and the quality of the isotherm fits should be reported. [ 46 ]…”

“…Recently, Long and co‐workers demonstrated the great potential of a flexible MOF Co(bdp) (bdp 2− : benzene‐1,4‐dipyrazolate) in ANG applications. [ 22,125 ] Co(bdp) exhibits an exceptionally high delivery capacity of 197 v/v from 6.5 to 0.5 MPa at 298 K. [ 22,65,99 ] The nitrogen adsorption isotherm of evacuated Co(bdp) at 77 K features five distinct steps between its collapsed phase of minimal porosity to its maximally expanded phase (Langmuir surface area of 2911 m 2 g −1 ), and is fully reproducible over at least 100 adsorption‐desorption cycles. [ 126,127 ] Another highlight is the intrinsically good thermal management of Co(bdp) due to its flexibility.…”