Optimizing nanoporous materials for gas storage

Abstract

aIn this work, we address the question of which thermodynamic factors determine the deliverable capacity of methane in nanoporous materials. The deliverable capacity is one of the key factors that determines the performance of a material for methane storage in automotive fuel tanks. To obtain insights into how the molecular characteristics of a material are related to the deliverable capacity, we developed several statistical thermodynamic models. The predictions of these models are compared with the classical thermodynamics approach of Bhatia and Myers [Bhatia and Myers, Langmuir, 2005, 22, 1688] and with the results of molecular simulations in which we screen the International Zeolite Association (IZA) structure database and a hypothetical zeolite database of over 100 000 structures. Both the simulations and our models do not support the rule of thumb that, for methane storage, one should aim for an optimal heat of adsorption of 18.8 kJ mol À1. Instead, our models show that one can identify an optimal heat of adsorption, but that this optimal heat of adsorption depends on the structure of the material and can range from 8 to 23 kJ mol À1. The different models we have developed are aimed to determine how this optimal heat of adsorption is related to the molecular structure of the material.

In silico Design of Porous Polymer Networks: High-Throughput Screening for Methane Storage Materials

“…The bulk material is then represented with a close packing of spheres as in Figure 4C, a modeling scheme previously proposed for analysis of PAF materials. 48 Because the carbon atoms of a shell are shared between multiple adsorption pockets, we define, as an approximation, the unit cell of our material as the sphere of radius R. We analyzed zeolites in the context of this model in our previous work 49 to capture a correlation between enthalpy and entropy change upon adsorption.…”

“…52 In our previous work, we showed that there is indeed an optimal heat of adsorption but that it depends on the pore size. 49 Second, the free volume in the material increases with increasing pore size because the carbon atoms in the shells take up a lesser fraction of the space occupied by the bulk material ( Figure S4a in the SI).…”

“…The presence of attractive methane−methane interactions gives rise to a higher deliverable capacity than could be achieved in the absence of these interactions. 49 Figure 8 displays the heat of adsorption at the charging pressure against that at the discharge pressure. Again, we see that structures with the highest deliverable capacities (color-coding in Figure 8) occur at an intermediate heat of adsorption.…”

Computational development of the nanoporous materials genome

“…Methane storage capacity is by far the most studied sorption property in the field of computational high throughput screening of nanoporous materials [27][28][29][30][31][32][33][34][35][36][37]83 . There are several reasons for this, the first being that there is considerable interest in safely and efficiently storing methane for use as an alternative, clean-burning fuel in motor vehicles.…”

“…Here, computational discovery is typically the first step, always to be followed by experimental work. It would seem obvious to adopt a similar strategy for nanoporous materials design, and sure enough in the past 5 years we have witnessed the proliferation of studies on virtual high-throughput screening of porous materials for gas capture and storage applications [27][28][29][30][31][32][33][34][35][36][37] .…”