Our experiments and density functional theory calculations indicate that the electrocatalyst’s activity is due to the specific property of each of its constituents, induced by their interactions. These findings help explain the high activity of Pt–Ru for methanol oxidation and the lack of it for ethanol oxidation, and point to the way to accomplishing the C–C bond splitting in other catalytic processes.

—Kowal et al. (2009)

Instead of using hydrogen as the energy carrier, or using a front-end fuel processor to reform a hydrocarbon liquid to produce hydrogen for use in a hydrogen fuel cell, a direct ethanol fuel cell directly converts ethanol (C₂H₅OH) to electricity, with H₂ and CO₂ as outputs:

Ethanol is one of the most ideal reactants for fuel cells. It’s easy to produce, renewable, nontoxic, relatively easy to transport, and it has a high energy density. In addition, with some alterations, we could reuse the infrastructure that’s currently in place to store and distribute gasoline.

—Brookhaven chemist Radoslav Adzic

A major hurdle to the commercial use of direct ethanol fuel cells is the molecule’s slow, inefficient oxidation, which breaks the compound into hydrogen ions and electrons that are needed to generate electricity. There are a number of efforts underway to develop a viable direct ethanol fuel cell, such as that at Kyushu Institute of Technology (KIT). The KIT team reported on their work with oxide nanoparticle composite electrodes for direct ethanol fuel cells at the 214^th Meeting of The Electrochemical Society in October. (The Brookhaven team also presented their work at ECS 214.)

Current–potential and current–time polarization curves comparing the activity of PtRhSnO2/C with several other catalysts for ethanol oxidation. Kowal et al. (2009) Click to enlarge.

The Brookhaven catalyst is made of platinum and rhodium atoms on carbon-supported tin dioxide nanoparticles. The electrocatalyst is capable of breaking carbon bonds at room temperature and efficiently oxidizing ethanol into carbon dioxide as the main reaction product. Other catalysts, by comparison, produce acetalhyde and acetic acid as the main products, which make them unsuitable for power generation.

Structural and electronic properties of the electrocatalyst were determined using x-ray absorption techniques at Brookhaven’s National Synchrotron Light Source, combined with data from transmission electron microscopy analyses at Brookhaven’s Center for Functional Nanomaterials.

Based on these studies and calculations, the researchers predict that the high activity of their ternary catalyst results from the synergy between all three constituents—platinum, rhodium, and tin dioxide—knowledge that could be applied to other alternative energy applications.

Next, the researchers will test the new catalyst in a real fuel cell in order to observe its characteristics first hand.

The work is supported by the Office of Basic Energy Sciences within DOE’s Office of Science.

Resources

• A. Kowal, M. Li, M. Shao, K. Sasaki, M. B. Vukmirovic, J. Zhang, N. S. Marinkovic, P. Liu, A. I. Frenkel & R. R. Adzic (2009) Ternary Pt/Rh/SnO₂ electrocatalysts for oxidizing ethanol to CO₂. Nature Materials, doi: 10.1038/nmat2359

• HaraYoshitaka Hara, Minoru Anai, Kazuyoshi Kamisugi, Shuji Hayase (2008) The high efficiency of a direct ethanol fuel cell having an oxide nanoparticle composite electrodes (Kyushu Institute of Technology)