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Regents professor Meilin Liu (right) and postdoctoral researcher Mingfei Liu examine a button fuel cell used to evaluate a new self-cleaning anode material based on barium oxide. The self-cleaning technique could allow fuel cells to be powered by coal gas. Credit: Georgia Tech Photo, Gary Meek.

The nation’s energy spotlight has drifted away from solid oxide fuel cells over the last year or so (the last big splash being the Bloom Energy media fest), but that doesn’t mean researchers aren’t still working to figure out how to overcome the barriers to making SOFCs commercially successful.

One of the main engineering barriers is operating temperature. The problem is that when SOFCs operate above 850 °C, the materials or other workarounds that have to be used to prevent performance problems are either expensive or require fuel dilution. Either way, they make these fuel cells cost prohibitive under current circumstances. Go below 850 °C and coking (carbon buildup) on traditional anode materials, such as Ni-yttrium-stabilized zirconia, causes deactivation and creates sharp drop offs in fuel-to-energy conversion. It’s a pity because these fuel cells could be fueled with waste hydrocarbon sources, such as municipal wastes and biomass, or could double the energy output of coal (gasified) and consequently cut CO₂ emissions in half.

But, a workgroup led by ACerS member Meilin Liu believes it has found a new way to make an SOFC anode, which can operate effectively and efficiently with carbonaceous fuels at 750 °C, using a nanostructured barium oxide/nickel interface. A paper about the group’s achievements was recently published in Nature Communications (doi:10:1038/ncomms1359). Liu, professor of MSE at Georgia Tech, and his research group collaborated with researchers at the Brookhaven National Lab, the New Jersey Institute of Technology and Oak Ridge National Lab.

The BaO possibilities were interesting to the group because the oxide is known to have been used as a promoter for reforming catalysts (the catalysts that breakdown hydrocarbon fuels into hydrogen and a byproduct). The challenge was to come up with a way of using the material that would not create a block to electrons but absorb water that would be used to remove carbon and combat coking. Their solution was to deposit (by evaporation) BaO onto Ni-YST. According to the authors, “In this process, BaO reacts with the surfaces of NiO, producing a thin film of NiO-BaO compounds on the NiO surface. On exposure to fuel, the thin film of NiO–BaO compounds is reduced to nanosized islands distributed on the Ni surface.”

Button-type test cells were made with the new anode structures. When fueled with dry C₃H₈, the cells attained a power density of ~0.88 Wcm^-2 at 750 °C (more than 50 percent higher that traditional SOFCs operated under the same conditions). Further, cells were able to produce a stable current of 500 mA cm^-2 for 100 hours, indicating the absence of coking.

Researchers also tested the new cells tolerance to CO. They used a wet (~3 v%) CO fuel stream and attained a power density of ~0.70 Wcm^-2 (again, higher than what has been reported for other SOFC under the same conditions).

Finally, they used a fluidized carbon bed–SOFC arrangement to test the anode’s possible performance with something like gasified coal. They formed the fuel stream using a wet CO₂ gasification technique. Here, they attained a peak power density of ~1.08 Wcm^-2 at 850 °C, twice that of other SOFCs. When they lowered the temperature to 750 °C, the cell peak power density was still remarkable: ~0.65 Wcm^-2 . Although cells cannot operate for long at this lower temperature, the the new anode delivered stable performance for 1000 hours.

The researchers say the performance and resistance to coking demonstrated using BaO/Ni interface “represent a vital step towards a cost-effecitve fuel cell for direct conversion of hydrocarbons and gasified carbonaceous solid fuels to electricity.”

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Hollow rods of titanium oxide with the solid manganese oxide core removed. (Credit: UConn.)

According to a University of Connecticut press release, researchers believe they have developed a new material that could be used as a catalyst in alternative fuel development.

Featured in the September issue of the nanotechnology journal, Small, University of Connecticut chemistry professor Steven Suib describes a method developed for the production of a nanosized crystalline material that can potentially be used for energy conservation.

Small fibers or rods of titanium oxide emanating from the manganese oxide-based template. (Credit: UConn.)

The material, sized at 100 nanometers, consists of two materials, one a template and the other a material that can grow around it in a well-ordered array. The growth can be controlled and its photocatalytic properties may be useful to drive reactions such as the splitting of water into hydrogen and oxygen.

According to Suib, the material can be a component of paint or can be applied to a surface, and will be useful in solar applications.

“It’s very hard to make materials this size,” Suib says, “as small antennas come in and out of a surface that small.”

Suib’s work with catalysts also expands to new oxygen reduction catalysts composed of octahedral molecular sieves of the the gamma form of manganese oxide (gamma-MnO2) and a small amount of titanium. We published a story on this work with active oxidation catalyst for Li-air batteries, which can be seen here.

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GreenTech reported that some aerogel companies are offering thin blankets that serve as replacements for traditional fiberglass, foam or cellulose insulation. It’s still more expensive upfront but the costs have fallen to the point that it can make sense in certain cases, particularly masonry or curved walls. The video posted above shows aerogel insulation over bent tubing.

Aerogels are made by removing the liquid from gels, resulting in a material that is more than 90 percent air. The porous structure of the nanomaterial makes it difficult for heat to pass through. As a result, aerogels make very good and light-weight insulators.

Aspen Aerogels says that its aerogel blankets have two to four times the insulating value per inch compared to fiberglass or foam. It’s also relatively easy to work with, allows water vapor to pass through and is fire resistant.

Material company Cabot has also developed its Nanogel insulator for buildings. Another company, ThermaBlok, has had its insulation used in demonstration houses built during last year’s Solar Decathlon home competition.

Contractors have started using the material on superinsulated homes that are sealed from the outside, both over masonry and under shingles. On wood frame homes, thin strips of aerogel can be applied to studs to prevent what’s called thermal bridging, where heat escapes through the walls’ framing.

Aspen provides this chart for for the R-value-philes (Spaceloft being Aspen’s brand name for their building insulation aerogel):

Read more about aerogel:

Aerogel markets report available

Aerogel-based -40°C hydration system to be licensed

Solar Decathlon entries make use of aerogel

Aeroclay research at Case Western

NASA’s aerogel grid captures amino acid in space

Cabot”s Nanogel aerogel insulation selected for 50 km of subsea pipelines

Artistic aerogel light demonstrations

Aerogel used in classic car remake

Aerogel’s potential to mop up oil spills

Aerogel has potential as tunable waveplate

Universe’s largest catcher’s mitt?

Birdair demonstrates aerogel membrane roofing systems

Nanotube aerogel sheets - better than real muscle?

Introduction to aerogel video

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