In Nature Materials paper, researchers describe new method to boost electron mobility, conductivity

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On June 4, 2018

Two Missouri S&T chemistry researchers are part of an international team that has designed a new metal-organic framework that exhibits dramatic improvements in electron mobility, which could lead to new applications for fuels cells, batteries and other technologies. The team describes its research in a Nature Materials paper published online today (Monday, June 4).

Dr. Gary J. Long, professor of chemistry, and Dr. Fernande Grandjean, adjunct professor of chemistry, are among the paper’s 16 authors. Lead author Dr. Jeffrey R. Long, professor of chemistry at the University of California, Berkeley, is a native of Rolla and Gary Long’s son. The team also includes other researchers from Berkeley and from Kyoto University in Japan, Universidad Andres Bello in Santiago, Chile, and Korea Research Institute of Chemical Technology in Daejeon, South Korea.

In the paper, the researchers describe how an iron-based metal-organic framework, or MOF, could be altered to greatly enhance its electric conductivity. Designed at the atomic level, MOFs are crystalline materials made up of metal sites connected by organic linkers. Their open framework makes them useful as porous materials and for use in gas storage, purification and separation.

The strong bonds between the metal and organic linkers are not conducive to electron flow, however. Combining both porosity and electric conductivity is “a worthy challenge” that makes these materials attractive for possible use as conductor devices for fuel cells, batteries and supercapacitors, Gary Long says.

Using a variety of testing methods – from spectroscopy and computational techniques to single-microcrystal field-effect transistor measurements – the researchers found that altering the iron-based MOF they studied resulted in “a nearly 10,000-fold enhancement in conductivity along a single crystallographic axis.” The alteration consisted of a partial reduction of iron(III) to iron(II) in a series of MOFs.

S&T researchers Long and Grandjean played a significant role in this research through their analysis of the Mössbauer spectral properties of the partially reduced compounds.

“If as is shown in our paper, reduction can increase the electron mobility in such compounds, they become attractive for use in various electronic applications,” Gary Long says. “This dramatic increase upon reduction has been nicely demonstrated by studying a single crystal of the compound in the form of a field-effect transistor,” as illustrated in Figure 1e of the paper.

The paper, titled “Electron delocalization and charge mobility as a function of reduction in a metal-organic framework,” was published online at 10 a.m. CDT (11 a.m. EDT, 4 p.m. London Time) today (Monday, June 4).

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