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September 2013

Not All Catalyst Morphologies Are Created Equal

Valuable chemical tools from non-precious materials

Paul Giokas

From cell phones to automobiles, batteries are crucial to everyday life. Emerging technologies require batteries or fuel cells that are compact, yet efficient. To be effective at reasonable temperatures, these systems require catalysts that enable reactions to proceed quickly. Unfortunately, many of the catalytic materials with the properties that match the needs of such batteries are precious metals -- as the name indicates, they are quite valuable, and their supply is limited. As a result, researchers are challenged to find and design new materials that function as effective catalysts.

The figure shows the different textures of (a) MnO nanoparticles on glassy carbon, (b) MnO nanoparticles on porous glassy carbon, and (c) MnO nanoparticles on porous glassy carbon after heat treatment.

Scientists with the Center on Nanostructuring for Efficient Energy Conversion (CNEEC) have uncovered a new manganese oxide (Mn3O4) catalyst to convert oxygen to water via the oxygen reduction reaction, an important process in metal-air batteries and in fuel cells. Manganese oxide (MnO) catalysts provide an alternative to well-known and commonly employed platinum, which is significantly more expensive and rare. Manganese oxide, on the other hand, is relatively abundant, as well as environmentally friendly. The oxygen reduction reaction is a complicated reaction, the steps of which are still being studied; however, it consists of oxygen from the atmosphere being reduced (gaining electrons) to first form peroxide and then water. In a battery, this reaction occurs at one electrode, while, at the other, a material is oxidized (loses electrons), and the movement of electrons between electrodes results in electrical current.

The researchers of the CNEEC loaded tiny MnO particles (14 nanometers in diameter) onto glassy carbon supports. Glassy carbon is a common material for electrodes, with some ability to reduce oxygen on its own. Therefore, to accurately determine how effectively the MnO operates as a catalyst, the researchers performed measurements that would discriminate between the support's and the catalyst's activity.

To determine the activity levels, they heated the glassy carbon support with and without catalyst present and took a series of measurements. The scientists learned that upon heating, the MnO was converted to Mn3O4, and the glassy carbon developed pores in its otherwise smooth surface. The change in morphology (that is, the change from the smooth to porous surface) corresponded to a significant change in effectiveness.

The Mn3O4, when tested as a catalyst, held its own against the best comparable non-precious metal catalysts. The ability of the catalyst/support to facilitate oxygen reduction in the way it did is exciting, especially given the relative abundance of the materials involved. The work shows Mn3O4 as a potential means to create efficient metal-air batteries that are affordable to produce. Further study is needed to examine the particular features that make the catalyst so effective. Understanding them better will lead to improved electrode design in energy storage and battery technology.

More Information

Gorlin Y, CJ Chung, D Nordlund, BM Clemens, and TF Jaramillo. 2012. "Mn3O4 Supported on Glassy Carbon: An Active Non-Precious Catalyst for the Oxygen Reduction Reaction." ACS Catalysis 2:2687-2694. DOI: 10.1021/cs3004352

Acknowledgments

The Center on Nanostructuring for Efficient Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, funded this research.

About the author(s):

  • Paul Giokas is a member of the Center for Solar Fuels at UNC Chapel Hill. He is a physical chemistry graduate student studying chromophore binding at semiconductor interfaces, as well as ultrafast dynamics with nonlinear spectroscopy in the Moran Group.

Affordable, Available Manganese-Based Catalyst Shows Its Worth for Energy Storage

Heat-treated particles on smooth supports out-perform other metal catalysts, answer key questions

MnO nanoparticles on porous glassy carbon after heat treatment.

Replacing gasoline with electricity in the nation's fleet of cars means building energy-dense batteries that are safe and affordable. The cost of batteries is related to the amount of precious metals they use. Scientists want to design batteries that use earth-abundant metals, such as manganese. Researchers studied catalytic manganese oxide nanoparticles on a glassy carbon support. By heating manganese with oxygen, they created Mn3O4 particles that require less energy to perform than the pre-heated form. This catalyst also effectively drives the reaction to completion. The catalyst's activity compares well with a state-of-the-art platinum/carbon catalyst and could open doors for manganese-air batteries. The Center on Nanostructuring for Efficient Energy Conversion, led by Stanford University, did the research.

More Information

Gorlin Y, CJ Chung, D Nordlund, BM Clemens, and TF Jaramillo. 2012. "Mn3O4 Supported on Glassy Carbon: An Active Non-Precious Catalyst for the Oxygen Reduction Reaction." ACS Catalysis 2:2687-2694. DOI: 10.1021/cs3004352

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.