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Chemists at UCLA Design Organic Structures Well-Suited for Gaseous Storage; The Lowest Reported Density of Any Crystal

The crystal structure of COF-108. Synthesized only from light elements (H,B,C,O) COF-108 is the lowest-density crystal ever produced (0.17 g/cm3). Click to enlarge. Credit: José L. Mendoza-Cortés

Chemists at UCLA have designed new organic structures for the storage of voluminous amounts of gases for use in alternative energy technologies.

The research, published in the journal Science, demonstrates how the design principles of reticular chemistry have been used to create three-dimensional covalent organic frameworks, which are entirely constructed from strong covalent bonds and have high thermal stability, high surface areas and extremely low densities.

Reticular chemistry deals with linking molecular building blocks by strong bonds into predetermined structures which can be functionalized and their metrics altered at will. The principles of reticular chemistry and the ability to construct chemical structures from these molecular building blocks has led to the creation of new classes of materials of exceptional variety.

Omar Yaghi (earlier post), UCLA professor of chemistry and biochemistry, led the team which comprises chemists from the Center for Reticular Chemistry at UCLA's California NanoSystems Institute and the departments of chemistry and biochemistry at UCLA.

The covalent organic frameworks, or COFs (pronounced "coffs"), one of these new classes of materials, are the first crystalline porous organic networks. A member of this series, COF-108, has the lowest density reported of any crystalline material, with a surface area of more than 4,500 square meters per gram.

One gram, unraveled, could cover the surface area of approximately 30 tennis courts.

These are the first materials ever made in which the organic building blocks are linked by strong bonds to make covalent organic frameworks. The key is that COFs are composed of light elements, such as boron, carbon and oxygen, which provide thermal stability and great functionality.

—Omar Yaghi

In the push to develop methods to control greenhouse gas emissions, some of the biggest challenges have been finding ways to store hydrogen for use as a fuel, to use methane as an alternative fuel, and to capture and store carbon dioxide from power plant smokestacks before it reaches the atmosphere. Yaghi and his colleagues believe COFs are uniquely suited for all these applications because of their functional flexibility and their extremely light weight, high porosity and thermal stability.

The research was funded by BASF, the National Science Foundation and the US Department of Energy.

A year ago, Yaghi and his team achieved hydrogen storage concentrations of up to 7.5 wt% in Metal Organic Framework (MOF) material—exceeding the DOE target of 6.5% by 2010 for application in hydrogen fuel-cell cars. (Earlier post.) BASF has licensed the technology and is moving forward on commercialization of MOFs.




Anybody have a guess on what improvement in gravimetric density this might yield for hydrogen storage vs the 7.5% for MOFs?


With these density to surface ratios one must consider the potential for electron storage - or utilization of this material as cathode/anode poles in chemical storage.

Rafael Seidl

While the research funding may be in hydrogen storage right now, COFs could eventually prove useful matrices for many other applications: CH4 storage, catalysts, DPFs, battery and ultracapacitor electrodes, mechanical cushioning, acoustic damping etc. It all depends on how easy they are to adapt to these tasks and how expensive they are to produce.

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