Aug
8
A New Super ION Conductor for Fuel Cells
August 8, 2008 | 1 Comment
First, not to be confused with a super conductor for electrons as we usually think of “super conductors,” this new material is about moving ions. That has important, perhaps huge implications for fuel cells.
Solid oxide fuel cell technology requires ion-conducting materials as in solid electrolytes that transport the oxygen ions from cathode to anode. Today’s materials do not provide atom-scale or small molecule size voids large enough to easily accommodate the path of a conducted ion, which is much bigger than, for example, those electrons that first came to mind.
The new material is made of layers, a “super lattice,” combining two materials that have very different crystal structures. The misalignment of the layer’s faces when joined distorts the interfacing zone making a path for ions to travel. The joined interface offers a lot of vacant spaces (the dimmed spheres in the graphic) instead of the holes that other materials offer as paths. Thus the difference is like running through trees vs. stuffing oneself though the small holes of a series of walls. Thus, ions move much faster, the press release is saying by a factor of nearly 100 million.
While electrical super conductors have to be deeply cooled to achieve their potential, in fuel cells the material needs to heated to high temperatures to gain porosity so “fast” conduct ions. The new, layered material maintains ionic conductivity near to room temperatures. That high temperature issue has been serious problem for fuel cell developers.
The researchers fabricated yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures where YSZ layers (with 8 mol% nominal yttria content) in the thickness range from 62 nm down to 1 nm were sandwiched between two 10-nm-thick layers of insulating SrTiO3 (STO). They also grew superlattices, alternating 10-nm-thick STO films with YSZ layers with thickness between 62 and 1 nm.
The dc conductivity of the 1-nm YSZ layer shows a record value of 0.014 S/cm at 357 K [83.85°C], with an activation energy of 0.64 eV and an extrapolated value of 0.003 S/cm at 300 K [26.85°C]. Thus, the threshold for the conductivity value that defines the feasibility for practical applications, 0.01 S/cm, is reached in these ultrathin films just slightly above room temperature.
—Garcia-Barriocanal et al. (2008)
The new information is from the innovative work at Spain’s Universidad Complutense de Madrid and Universidad Politécnica de Madrid who produced the material and observed its outstanding conductivity properties. The analysis was done by the U.S. Oak Ridge National Laboratory using the 300 kilovolt Z-contrast scanning transmission microscope.
The Spanish websites have no discernable press release page nor does the Oak Ridge press release name the members of the Spanish team. The Oak Ridge release says the paper jointly prepared by the Spaniards and Americans published August 1, 2008 in Science, (behind the pay barrier) Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures. Science Vol. 321. no. 5889, pp. 676 – 680. The paper does name J. Garcia-Barriocanal, A. Rivera-Calzada, M. Varela, Z. Sefrioui, E. Iborra, C. Leon.
The Oak Ridge people are Maria Varela of the Materials Science and Technology Division and senior researcher Stephen Pennycook. Ms. Varela is justifiably quite impressed too, saying, “(Its) a colossal increase in ionic conduction properties. It is amazing,” she said. “We can see the strained, yet still ordered, interface structure that opens up a wide pathway for ions to be conducted.”
What we don’t know is how the lattice layers are made up, a sense of the costs, longevity and other matters. But something astonishing happened; an innovative view to solve a problem with unalike materials joined to form these paths was brought to fruition. That’s a giant step in the march to efficient and easy to use fuel cells. That 100 million factor in transporting ions is no small matter if usability and production to integration in fuel cells comes to pass.
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[…] Solid oxide fuel cell technology requires ion-conducting materials as in solid electrolytes that transport the oxygen ions from cathode to anode. Today’s materials do not provide atom-scale or small molecule size voids large enough to … Read More […]