Fuel Cell Cathode Surface Strontium Sulfate Phase Crack Suppression
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Solution Overview
Problem
Micro-cracks that form near the surface of the cathode in fuel cells during firing can lead to crack formation over time, affecting the cathode's integrity during long-term operation.
Innovation Solution
Incorporating a secondary phase of strontium sulfate within the cathode's surface region, with an occupied surface area ratio of 0.25% to 8.5%, enhances the structural strength and inhibits the formation of micro-cracks, thereby preventing crack propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cathode is fired at high temperature to form perovskite oxide, then the cathode achieves proper electrochemical performance, but micro-cracks form in proximity to the surface during firing
Solution Approach 1:
The invention applies local quality by creating a surface region with different composition and properties from the bulk cathode. The surface region within 5 μm from the surface contains strontium sulfate secondary phase with occupied surface area ratio of 0.25% to less than or equal to 8.5%, which suppresses micro-crack formation specifically at the surface where cracks originate, while maintaining the perovskite oxide main phase for electrochemical performance throughout the cathode bulk.
Solution Approach 2:
The invention uses composite materials by combining perovskite oxide as the main phase with strontium sulfate as a secondary phase in the surface region. This composite structure leverages the electrochemical activity of perovskite oxide while utilizing strontium sulfate's crack-suppressing properties, creating a multi-functional surface layer that simultaneously maintains performance and prevents structural degradation.
2Strength
If the cathode surface is made dense to prevent crack formation, then structural strength improves, but gas transport and electrochemical activity may be reduced
Solution Approach 1:
The invention applies local quality by restricting the strontium sulfate secondary phase specifically to the surface region within 5 μm from the surface, with controlled occupied surface area ratio of 0.25% to less than or equal to 8.5%. This localized modification provides crack suppression exactly where micro-cracks originate at the surface, while the bulk cathode maintains its porous perovskite oxide structure for optimal gas transport and electrochemical activity.
Data Source
AI summary
A fuel cell has an anode, a cathode and a solid electrolyte layer. The cathode contains a perovskite oxide as a main component. The perovskite oxide is expressed by a general formula ABO3 and includes at least Sr at the A site. The solid electrolyte layer is disposed between the anode and the cathode. The cathode includes a surface region which is within 5 μm from a surface opposite the solid electrolyte layer. The surface region contains a main phase containing the perovskite oxide and a secondary phase containing strontium sulfate. An occupied surface area ratio of the secondary phase in a cross section of the surface region is greater than or equal to 0.25% to less than or equal to 8.5%.