Researchers at Berkeley Lab Develop New ANG Technology

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory have developed a variety of metal–organic frameworks (MOFs)—sponge-like 3D crystals with a large internal surface area—that feature flexible gas-adsorbing pores. This flexibility gives these MOFs a high capacity for storing methane, which in turn has the potential to help make the driving range of an adsorbed-natural-gas (ANG) car comparable to that of a typical gasoline-powered car.

Jeffrey Long, a chemist with Berkeley Lab’s Materials Sciences Division and the University of California Berkeley, is the corresponding author of a Nature paper that describes the work entitled, “Methane storage in flexible metal–organic frameworks with intrinsic thermal management.” The lead author is Jarad Mason, a member of Long’s research group at the time of this study and now at Northwestern University.

The key to the success of the MOFs developed by Long, Mason and their colleagues is a “stepped” adsorption and desorption of methane gas. “Most porous materials that would be used as adsorbents exhibit classical Langmuir-type isotherm adsorption, where the amount of methane adsorbed increases continuously but with a decreasing slope as the pressure is raised so that, upon discharging the methane down to the minimum delivery pressure, much of it remains in the tank,” Long says. “With our flexible MOFs, the adsorption process is stepped because the gas must force its way into the MOF crystal structure, opening and expanding the pores.” This means the amount of methane that can be delivered to the engine, i.e., the usable capacity, is higher than for traditional, non-flexible adsorbents.”

In addition, Long says, the step in the adsorption isotherm is associated with a structural phase change in the MOF crystal that reduces the amount of heat released upon filling the tank, as well as the amount of cooling that takes place when methane is delivered to accelerate the vehicle.

This research was supported by the DOE’s Advanced Research Projects Agency – Energy (ARPA-E). The X-ray characterizations were carried out at synchrotron light sources that included theAdvanced Light Source and the Advanced Photon Source, both DOE Office of Science User Facilities.