Thermal Expansion Matching as a Key Criterion for Developing High-Performance Mn-based Mullite Cathodes in SOFCs

Area of Science:

• Materials Science
• Electrochemistry
• Solid Oxide Fuel Cells

Background:

• Thermal expansion mismatch is a critical issue in solid oxide fuel cell (SOFC) cathode design, leading to delamination and cracking.
• Developing cathode materials with both structural integrity and high catalytic activity is essential for SOFC performance and longevity.

Purpose of the Study:

• To design and develop a novel Mn-based mullite-type cathode material, SmMn2O5 (SMO), for SOFCs.
• To investigate the structure-property relationships of SMO-based composite electrodes with GDC for improved thermal expansion matching and electrochemical performance.
• To provide a new strategy for SOFC cathode development by prioritizing thermal expansion coefficient (TEC) matching.

Main Methods:

• Fabrication of SmMn2O5 (SMO) and SMO-GDC composite electrodes.
• Measurement of thermal expansion coefficient (TEC) and electrochemical performance.
• In situ X-ray diffraction (XRD), Raman spectroscopy, and density functional theory (DFT) analysis to understand structure-property relationships.

Main Results:

• SMO exhibited a low TEC (8.12 × 10^-6 K^-1) attributed to anisotropic lattice expansion and phonon scattering.
• The SMO-GDC composite showed excellent TEC matching with YSZ, with only 2.36% deviation.
• The composite cathode achieved a power density of 580.9 mW cm^-2, with a polarization resistance of 0.193 Ω cm^2, and maintained stability for 300 hours.

Conclusions:

• The developed SMO-GDC composite cathode offers superior structural stability and high electrochemical activity for SOFC applications.
• Prioritizing TEC matching as a primary design principle is effective for developing advanced SOFC cathode materials.
• This work provides valuable insights into material selection strategies for next-generation SOFCs.