As a cleaner and more evenly distributed fuel, natural gas has significant advantages over petroleum as a source of energy for the transportation sector. Despite the potential benefits of natural gas, its low volumetric energy density at ambient temperature and pressure presents substantial challenges, particularly for light-duty passenger vehicles that have little extra space available for on-board fuel storage. Adsorbed natural gas systems have the potential to eliminate these issues by storing high densities of methane within a porous material at ambient temperature and reduced pressures. Although activated carbons, zeolites, and metal-organic frameworks have been investigated extensively for natural gas storage, there are still no commercially available adsorbed natural gas vehicles, owing to the challenges involved in designing a practical storage system with a high capacity of usable CH4, sufficient thermal management, and a low cost. Here, we introduce a new concept in gas storage, wherein a reversible phase transition is used to maximize the deliverable capacity of a gas while also providing internal heat management during adsorption and desorption. In particular, the flexible metal-organic frameworks Co(bdp) and Fe(bdp) (bdp2– = 1,4-benzenedipyrazolate) are shown to undergo a structural phase transition in response to specific CH4 pressures, resulting in adsorption and desorption isotherms that feature a sharp step. Such behavior enables storage capacities that push beyond the limits of classical adsorbents, while also reducing the amount of heat released during CH4 adsorption and the impact of cooling during desorption. Significantly, the pressure and energy associated with the phase transition can be tuned either chemically or by application of mechanical pressure.

High-capacity methane storage in flexible metal-organic frameworks with internal thermal management

251st National Meeting (2016)

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