Wednesday, April 22, 2009

Toothepaste Compound Brings Big Hydrogen Solar Breakthrough

Titania, titanium dioxide, titanium white, or CI 77891. Mythic stuff. It's used everywhere: semiconductors, oxygen sensors, protein cleaver... food coloring, sun tan lotion, kitty litter! When you see fake snow in a movie... that's pigment white 6!

The egg-heads of Northeastern University, and the National Institute of Standards and Technology (NIST), have gone further to display the potential, demonstrate its value, why it's paramount to fulfilling the 35-year dream of hydrogen fuel cells inspired by Akira Fujishima (link):

Increasing the available surface area is one way to boost a catalyst's performance, so a team at Northeastern has been studying techniques to build tightly packed arrays of titania nanotubes, which have a very high surface to volume ratio. They also were interested in how best to incorporate carbon into the nanotubes, because carbon helps titania absorb light in the visible spectrum. (Pure titania absorbs in the ultraviolet region, and much of the ultraviolet is filtered by the atmosphere.)

This brought them to the NIST X-ray spectroscopy beamline at the National Synchrotron Light Source (NSLS)**. The NIST facility uses X-rays that can be precisely tuned to measure chemical bonds of specific elements, and is at least
10 times more sensitive than commonly available laboratory instruments, allowing researchers to detect elements at extremely low concentrations. While making
measurements of the carbon atoms, the team noticed spectroscopic data indicating
that the titania nanotubes had small amounts of potassium ions strongly bound to the surface, evidently left by the fabrication process, which used potassium
salts. This was the first time the potassium has ever been observed on titania nanotubes; previous measurements were not sensitive enough to detect it.

The result was mildly interesting, but became much more so when the research team compared the performance of the potassium-bearing nanotubes to similar arrays deliberately prepared without potassium. The former required only about one-third the electrical energy to produce the same amount of hydrogen as an equivalent array of potassium-free nanotubes. "The result was so exciting," recalls Northeastern physicist Latika Menon, "that we got sidetracked from the carbon research." Because it has such a strong effect at nearly undetectable concentrations, Menon says, potassium probably has played an unrecognized role in many experimental water-splitting cells that use titania nanotubes, because potassium hydroxide is commonly used in the cells. By controlling it, she says, hydrogen solar cell designers could use it to optimize performance.

- Brewskie

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