Flexible porous materials improve methane storage

Finding alternative energy sources to replace conventional fossil fuels is crucial for fighting climate change. This task is especially difficult for vehicles, which need energy-dense, portable fuels that can be transported safely. Hydrogen and methane are two promising, less harmful alternative fuel options, but both are lightweight gases that traditionally need to be stored at high pressures and low temperatures to be viable.

Forrest et al. reviewed flexible metal-organic frameworks, which can provide an alternative method for storing methane while avoiding the need for cooled and pressurized tanks.

“When you put methane into one of these porous metal-organic frameworks, the intermolecular interactions are strong enough to change the range of pressures at which methane can enter the pores at high densities,” said author Brian Space.

Porous materials have previously been explored for their ability to absorb and store methane safely. The framework allows the gas to bind and form droplets, increasing the density without high pressures or low temperatures. This binding process generates a substantial amount of waste heat.

A new class of materials, flexible metal-organic frameworks, can expand and increase the effective storage volume by using the heat generated by the binding process as work to open the material pores. The team examined several of these types of materials, discussing their relative merits and potential applications.

“We’re just beginning to explore all the possibilities that are available to us,” said Space. “There are so many possibilities for pores and flexibility. This is an exploration of what has been found so far.”

Source: “Methane storage in flexible and dynamical metal-organic frameworks,” by Katherine Forrest, Gaurav Verma, Yingxiang Ye, Junyu Ren, Shengqian Ma, Tony Pham, and Brian Space, Chemical Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0072805 .