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Research Papers

Increased Cathodic Kinetics on Platinum in IT-SOFCs by Inserting Highly Ionic-Conducting Nanocrystalline Materials

[+] Author and Article Information
Hong Huang

Department of Mechanical Engineering, Stanford University, CA 94305; Department of Mechanical and Materials Engineering, Wright State University, OH 45435

Tim Holme

Department of Mechanical Engineering, Stanford University, CA 94305

Fritz B. Prinz

Department of Mechanical Engineering, Stanford University, CA 94305; Department of Materials Science and Engineering, Stanford University, CA 94305

While the fluorite structure is not the stable low-temperature phase for the undoped materials, only relative comparisons of energy between two structures in the fluorite phase were sought; therefore, it is thought that for comparison purposes, the calculations will reproduce the correct trends.

J. Fuel Cell Sci. Technol 7(4), 041012 (Apr 08, 2010) (5 pages) doi:10.1115/1.4000632 History: Received August 22, 2008; Revised July 24, 2009; Published April 08, 2010; Online April 08, 2010

One of the crucial factors for improving intermediate-temperature solid oxide fuel cell (SOFC) performance relies on the reduction in the activation loss originating from limited electrode reaction kinetics. We investigated the properties and functions of the nanocrystalline interlayer via quantum simulation and electrochemical impedance analyses. Electrode impedances were found to decrease several folds as a result of introducing a nanocrystalline interlayer and this positive impact was the most significant when the interlayer was a highly ionic-conducting nanocrystalline material. Both exchange current density and maximum power density were highest in the ultrathin SOFCs (fabricated with microelectromechanical systems (MEMS) compatible technologies) consisting of a 50 nm thick nano-gadolinia doped ceria (GDC) interlayer. Oxygen vacancy formation energies both at the surface and in the bulk of pure zirconia, ceria, yttria-stabilized zirconia, and GDC were computed from density functional theory, which provided insight on surface oxygen vacancy densities.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) ZrO2 structure. Arrows point to the 4 O atom kink on the surface. (b) A supercell of (111) YSZ with 38-Pt cluster used to calculate the charge transfer activation barriers.

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Figure 2

Schematic configurations of (a) symmetric structure for electrochemical impedance analyses and (b) the UTSOFC architecture with cathodic interlayer

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Figure 3

AFM images of the YSZ plate and sputtered YSZ films showing the difference in grain sizes. Left: 200 μm thick YSZ and right: dc sputter YSZ.

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Figure 4

Typical electrochemical impedance spectra of symmetric systems under no potential polarization: Pt/50 nm thick nanocrystalline interlayer/200 μm microcrystalline YSZ/50 nm thick nanocrystalline interlayer/Pt. Spectra obtained at 500°C and the area is 0.5 cm2.

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Figure 5

(a) Cross-section SEM images of ultrathin SOFCs consisting of 80 nm Pt cathode, 50 nm GDC interlayer, 50 nm YSZ electrolyte, and 80 nm Pt anode; and (b) I-V characteristics obtained at 350°C of different UTSOFCs. All the electrodes (cathode and anode) are 80 nm thick porous Pt.

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Figure 6

Bar plot comparing exchange current density obtained from UTSOFCs and ionic conductivity of the materials, adjacent of cathode Pt

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