Stress Distribution in Proton Conducting Oxide under Fuel Cell Operation Conditions

Tatsuya Kawada^a, Taisei Segami^a, Ryuta Sato^a, Soichiro Ebata^a, Satoshi Watanabe^a, Riyan Budiman^a^,^b, Mina Yamaguchi^a, Keji Yashiro^a^,^c, Koji Amezawa^d

^aGraduate School of Environmental Studies, Tohoku University, Japan

^bResearch Center for Advanced Material, National Research and Innovation Agency (BRIN), Indonesia

^cFaculty of Material for Energy, Shimane University, Japan

^dInstitute of Interdisciplinary Research for Advanced Materials, Tohoku University, Japan

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Devices for a Net Zero World

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Keynote, Tatsuya Kawada, presentation 299
Publication date: 10th April 2024

One of the major problems with proton-conducting oxide fuel cells is the large chemical expansion upon hydration and the resulting mechanical stress within the electrolyte. The purpose of this study was to establish a method for numerical calculation of stress distribution under fuel cell (and electrolysis) operating conditions and a method for experimental verification of the estimated results. In this study, Ba(Zr,Y)O3 and Ba(Zr,Yb)O3 were selected as the target proton-conducting oxides. First, the lattice volume change was modeled using published thermodynamic parameters of defect equilibrium, along with experimental results from high-temperature X-ray diffraction. Although a significant change in lattice volume was observed upon hydration, the influence of redox reactions was found to be negligible. Then the elastic modulus of the material was measured using a resonance method at elevated temperatures in controlled atmospheres. The chemical potential distribution of oxygen and hydrogen (and water vapor) under fuel cell (or electrolysis) conditions were estimated using an equivalent circuit containing three transmission lines, for proton, oxide ion, and hole, terminated by gas-solid exchange reaction resistors for oxygen, hydrogen, and water. The obtained proton concentration distribution was used to calculate the chemical strain distribution across the sample. The stress distribution and deformation of the electrolyte were calculated for the free-standing and constrained states. The information of the deformation of the free-standing sample was used for experimental validation of the calculated results. In the verification experiment, a sample pellet with Pt and Pd electrodes on the air and fuel sides of the surface was placed on a quartz tube with using mica as a gas sealant, and the surface profile was measured using a reflection-type laser profilometer. When the water vapor partial pressure on the air side was increased, the sample deformed concavely toward the fuel side. This change was confirmed reversible by increasing and decreasing the water vapor pressure. The amount of deformation agreed well with the calculated value, confirming that the calculated results were valid.

Acknowledgements:

This study was partly supported by the New Energy and Industrial Technology Development (NEDO), Japan.

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