With computers and the power of basic physics, chemistry and quantum mechanics, Ozolins group decided to take a step back and analyze the sodium alanate in its pure form, without added titanium. The group analyzed the atomic processes occurring in the material and what happens to the chemical bond between the hydrogen and the material at the temperatures of hydrogen release. The computation gave the researchers information that would have been very difficult to obtain experimentally.
The computation suggested a reaction mechanism that is essential for the extraction of hydrogen from the material which involves diffusion of aluminum ions within the bulk of the hydride. By comparing the calculated activation energies to the experimentally determined values, Ozolins group found that aluminum diffusion is the key rate limiting process in materials catalyzed with titanium. Thus, titanium facilitates processes in the material that are essential for turning on this mechanism and extracting hydrogen at lower temperatures.
This method and this knowledge can now be used to analyze other materials that would make for better storage systems than sodium alanate. We are still on the fundamental end of the study. But if we can figure this out computationally, the people with the technology in engineering can figure out the rest, said Hakan Gunaydin, a UCLA graduate student in Ozolins lab and another one of the studys authors.
Sodium alanate in itself is a prototypical complex hydride with a reasonable storage density and very good kinetics. Hydrogen goes in and comes out quickly but it wouldnt be practical for a car simply because it doesnt contain enough hydrogen. So thats why we are so interested in understanding how the hydrogen comes out, what happens exactly and how we can take this to other materials, said Ozolins.
What Ozolins group, along with UCLA chemistry and biochemistry professor Kendall Houk, also a member of the California Nan
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University of California - Los Angeles