In-situ Measurement of Internal Stresses in Solid Oxide Fuel Cells during Thermal Cycling by Synchrotron Radiation
Hirofumi SUMI, Yasunobu MIZUTANI, Yoshihisa DOI, Yoshiaki AKINIWA and Keisuke TANAKA
Abstract:The internal stress resided in anode-supported solid oxide fuel cells (SOFCs) was measured by high-energy X-rays from synchrotron radiation at beam line BL02B1 of Spring-8. Firstly, the X-ray elastic constants of cubic scandia stabilized zirconia (c-ScSZ) electrolyte and NiO anode were determined using laboratory X-rays. Using these values, the internal stress in unit cells was determined by the constant penetration depth method with high-energy X-rays of 71.91 keV. The internal stress in electrolyte of oxidized cells measured at the room temperature was a compression of about 400 Mpa and this was produced by the mismatch of the coefficient of thermal expansion between anode and electrolyte. The internal stress in NiO anode was tension of about 100 Mpa. The internal stress in electrolyte of reduced cells was about a compression of 100 Mpa. In-situ measurements of the internal stress in an oxidized cell were conducted during thermal cycling. The compressive stress in e! Lectrolyte decreased with increasing temperature and became nearly zero at 1000 K, while the tensile stress in anode decreased with increasing temperature and diminished at 1000 K. The coefficients of thermal expansion both of anode and electrolyte were almost same value above 1000 K, which agreed with the measured change of the internal stress. The internal stresses in both electrolyte and anode returned to the initial values after thermal cycling. Key Words:Solid oxide fuel cell (SOFC), Internal stress, Synchrotron radiation, Constant penetration depth method, Thermal cycle