Until a few years ago, the upper limit for surface area of porous materials was thought to be around 3,000 m² g^-1. Then, In 2004, a U-M team led by Dr. Omar Yaghi (now at UCLA) that included Matzger reported development of a metal organic framework (MOF) material known as MOF-177 that set a new record with an estimated surface area of 4,500 m² g^-1. (Earlier post.)

MOFs are scaffold-like structures made up of metal hubs linked together with struts composed of organic compounds.

The new material, UMCM-2 (University of Michigan Crystalline Material-2) is a coordination polymer comprising three types of microporous cages derived from zinc-mediated coordination copolymerization of a dicarboxylic and tricarboxylic acid. Previously, the researchers used the same method to create a similar material, UMCM-1, which was made up of six, microporous cage-like structures surrounding a large, hexagonal channel.

By using a slightly different combination of ingredients, Matzger’s group came up with UMCM-2, which is composed of fused cages of various sizes and does not have the channel found in UMCM-1. Despite their exceptional porosity, both of these coordination polymers (UMCM-1 and UMCM-2) are thermally robust.

Hydrogen uptake for UMCM-2 approaches 7 wt% at 77 K (-196 °C or -321 °F)—no greater than that of existing materials in the same family, suggesting that surface area alone is not the key to hydrogen uptake, according to the researchers.

Even so, UMCM-2 is useful for helping define future research directions, Matzger said. “I think we needed this compound to demonstrate that high surface area alone is not enough for hydrogen storage.”

Matzger’s coauthors on the paper are postdoctoral researcher Kyoungmoo Koh and research scientist Antek Wong-Foy. The researchers received funding from the US Department of Energy.

Resources

• Kyoungmoo Koh, Antek G. Wong-Foy and Adam J. Matzger (2009) A Porous Coordination Copolymer with over 5000 m²/g BET Surface Area. J. Am. Chem. Soc., Article ASAP DOI: 10.1021/ja809985t