0
Research Papers

# Stabilization of a Zirconia System and Evaluation of Its Electrolyte Characteristics for a Fuel Cell: Based on Electrical and Mechanical Considerations

[+] Author and Article Information
Akihiko Yamaji, Takao Koshikawa, Tadaharu Adachi

Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama-shi, Saitama 338 8570 Japan

Wakako Araki1

Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama-shi, Saitama 338 8570 Japanaraki@mech.saitama-u.ac.jp

1

Corresponding author.

J. Eng. Mater. Technol 131(1), 011010 (Dec 18, 2008) (6 pages) doi:10.1115/1.3026557 History: Received December 12, 2007; Revised May 27, 2008; Published December 18, 2008

## Abstract

The purpose of this study is to clarify the relationship between ionic conductivity and phase transformation of zirconia system codoped with scandium oxide $Sc2O3$ and ytterbium oxide $Yb2O3$. Aiming to achieve high ionic conductivity as well as high mechanical strength, the authors have also investigated the relationship between phase transformation and mechanical strength. The results have been discussed with respect to both the conductivity and the mechanical strength. The Sc- and Yb-codoped zirconia $(ZrO2)$ used as samples in this study were prepared by a standard solid-state reaction. X-ray powder diffraction (XRD) method was used to determine the crystal structures of the sintered samples. To detect any phase change between room temperature and $1273K$, thermal mechanical analysis (TMA) was conducted. To determine oxygen-ion conductivity in a temperature range from $873to1273K$ in air, impedance measurements were performed with alternating current (ac). Single-cell performance was confirmed under the condition of $26.2Pa$ partial hydrogen pressure. Finally, to measure bending strength, three-point bending tests were performed with a universal testing machine. The results of XRD and TMA showed that codoping of $Sc2O3$ and $Yb2O3$ into $ZrO2$ successfully stabilized the cubic phase when the average radius ratio of these two dopants in total was close to the ideal one for the eight-coordinate. The ac impedance measurement demonstrated that the cubic-phase stabilization achieved a high conductivity. Adequate amounts of dopants produced oxygen vacancies for high conductivity without complex defects: $ZrO2$ system doped with $1mol%$ of $Yb2O3$ and $8mol%$ of $Sc2O3$ showed the highest conductivity at $1273K$ and $0.30S∕cm$. The bending strength decreased with increasing the content of doped $Sc2O3$ from $7mol%to11mol%$, depending on the amount of the tetragonal phase, which contributes to strengthen materials. In the performance test, the $ZrO2$ system stabilized with doping $1mol%$$Yb2O3$ and $8mol%$$Sc2O3$ with thickness of $2.16mm$ showed maximum power density at $1273K$, that is, $210mW∕cm2$. From all the above tests, we recommend that, based on electrical and mechanical considerations, 1Yb8ScSZ is the present best option for an electrolyte material for a solid oxide fuel cell.

###### FIGURES IN THIS ARTICLE
<>
Copyright © 2009 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

## Figures

Figure 1

X-ray powder diffraction patterns

Figure 2

SEM pictures: (a) 9ScSZ and (b) 2Yb8ScSZ

Figure 3

Thermal expansion and phase transition

Figure 4

Ionic conductivity: (a) ScSZ, (b)1Yb yScSZ, and (c) 2Yb yScSZ

Figure 5

Arrhenius plot of ionic conductivity

Figure 6

Bending strength

Figure 7

Results of single-cell performance test: (a) 1073K and (b) 1273K

Figure 8

Maximum power density and ionic conductivity

## Discussions

Some tools below are only available to our subscribers or users with an online account.

### Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related Proceedings Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

• TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
• EMAIL: asmedigitalcollection@asme.org
Sign In