Biorefinery facilities are critical to fueling the economy—converting wood chips, grass clippings, and other biological materials into fuels, heat, power, and chemicals.
A research team at the US Department of Energy's (DOE's) Oak Ridge National Laboratory has now discovered a way to create functional materials from the impure waste sugars produced in the biorefining processes.
Using hydrothermal carbonization, a synthesis technique that converts biomass into carbon under high temperature and pressure conditions, the team transformed waste sugar into spherical carbon materials. These carbon spheres could be used to form improved supercapacitors, which are energy storage devices that help power technologies including smartphones, hybrid vehicles, and security alarm systems. The team's results are published in Scientific Reports, a Nature research journal.
"The significant finding is that we found a way to take sugar from plants and other organic matter and use it to make different structures," said Amit Naskar, a senior researcher in ORNL's Materials Science and Technology Division. "Knowing the physics behind how those structures form can help us improve components of energy storage."
By modifying the synthesis process, the researchers created two varieties of the novel carbon spheres. Combining sugar and water under pressure resulted in solid spheres, whereas replacing water with an emulsion substance (a liquid that uses chemicals to combine oil and water) typically produced hollow spheres instead.
"Just by substituting water for this other liquid, we can control the shape of the carbon, which could have huge implications for supercapacitor performance," said Hoi Chun Ho, a Ph.D. candidate working with Naskar at the Bredesen Center for Interdisciplinary Research and Graduate Education, a joint venture of ORNL and the University of Tennessee, Knoxville. The team also discovered that altering the duration of synthesis directly affected the size and shape of the spheres.
To further explore the discrepancies between solid and hollow carbon structures, the team ran synthesis simulations on the Cray XK7 Titan supercomputer at the Oak Ridge Leadership Computing Facility (OLCF), a DOE Office of Science User Facility located at ORNL. They also used transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) tools at the Center for Nanophase Materials Sciences (CNMS), another DOE Office of Science User Facility, to characterize the capabilities and structure of the carbon samples.
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