Hydration-induced stiffness enabling robust thermal cycling of high temperature fuel cells cathode
Hongxin Yang, Yuan Zhang, Zhipeng Liu, Chunfang Hu, Junbiao Li, Hailong Liao, Minhua Shao, Meng Ni, Bin Chen, Zongping Shao, Heping Xie
Abstract
Thermo-mechanics of cathode is closely related to the durability of high-temperature solid oxide fuel cells (SOFCs), with two main mechanical failures during thermal cycling: interface delamination and bulk cracking of cathode. Bulk cracking, caused by insufficient fracture strength/stiffness is a big concern but often overlooked. Here, we introduce chemical hydration to offset the thermal expansion, enhancing the cathodic mechanical stiffness and fracture strength, thus promoting the thermo-mechanical durability of cathode in proton ceramic fuel cells (PCFCs). Such chemical-induced expansion offset is achieved by strengthening intergranular bonding inside the bulk cathode after the hydration, preventing granule detachment during thermal shrinkage. As a demonstration, the stiffness-enhanced air electrode (BaCo0.7Ce0.15Y0.15O3, noted as s-BCC-Y) exhibits 86% enhancement of fracture strength, thus thermal cycling stability with almost no degradation after 35 harsh thermal cycles between 600 and 300 °C, surpassing pristine BaCo0.7Ce0.3O3 and many cobalt-free PCFC cathodes. Benefitted from the improved stiffness of cathode, full cell with the s-BCC-Y electrode demonstrates enhanced power output. This work highlights the importance of bulk cathode thermo-mechanics in developing robust SOFCs for high temperature energy applications. High-temperature fuel cells often face bulk cracking due to insufficient fracture strength and stiffness. Here, the authors show that chemical hydration enhances cathode mechanical properties, significantly improving thermal cycling stability and overall performance in proton ceramic fuel cells.