Anisotropic CTE Lanthanum Strontium Manganite SOFC Cathode
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Solid oxide fuel cells (SOFCs) face thermal mismatch stress issues due to coefficient of thermal expansion (CTE) mismatches between anode and cathode materials, leading to potential fracture and failure, especially when cooling from high sintering temperatures to room temperature.
Innovation Solution
A cathode with anisotropic CTE is developed, where the out-of-plane and in-plane CTE values differ by at least 1×10−6° C−1, achieved by sintering a perovskite layer under pressure, which can be applied to the SOFC stack either separately or simultaneously with other layers, reducing thermal mismatch stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional isotropic CTE cathode materials (e.g., LSM with Sr content ≥0.2) are used to achieve good electrochemical performance, then the CTE mismatch stress with the electrolyte increases, but the electrochemical performance is maintained; however, this leads to increased thermal mismatch stress and potential fracture during cooling
Solution Approach 1:
The cathode is designed with anisotropic CTE properties where the in-plane CTE is specifically engineered to match the electrolyte CTE, while the out-of-plane CTE can differ. This local differentiation of thermal expansion characteristics in different directions allows the cathode to maintain both good electrochemical performance and reduced thermal mismatch stress with the electrolyte during temperature changes.
Solution Approach 2:
The invention changes the CTE parameter from isotropic to anisotropic by controlling the sintering process under specific conditions. By applying pressure during sintering, the cathode material develops different CTE values in different directions, with the in-plane CTE being reduced to match the electrolyte's CTE, thereby reducing thermal mismatch stress while maintaining electrochemical performance.
2Productivity
If rapid cooling is applied to reduce manufacturing time, then productivity increases, but the thermal mismatch stress causes fracture and failure of the SOFC
Solution Approach 1:
The cathode is pre-conditioned through controlled sintering under pressure to develop anisotropic CTE properties before the final assembly and cooling process. This preliminary action of creating anisotropic CTE structure ensures that the cathode is pre-adapted to minimize thermal stress during subsequent rapid cooling, allowing both high productivity and reliability.
3Stress or pressure
If the CTE of the cathode is reduced to match the electrolyte CTE, then thermal mismatch stress decreases, but the Sr content must be reduced below 0.2, which diminishes electrochemical performance
Solution Approach 1:
The invention introduces asymmetry in the CTE properties of the cathode material by creating anisotropic thermal expansion characteristics. The in-plane CTE is reduced to match the electrolyte, while the out-of-plane CTE maintains properties suitable for electrochemical performance. This asymmetric CTE distribution allows the cathode to simultaneously achieve low thermal mismatch stress and good electrochemical performance without compromising Sr content.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The anisotropic CTE cathode minimizes thermal mismatch stresses in SOFCs, reducing the likelihood of failure during temperature changes, as demonstrated by lower CTE values and non-linear stress-strain curves, thereby enhancing the durability of the fuel cell.
Implementation Method 1
a sintered layer having an anisotropic coefficient of thermal expansion (CTE) defined by an out-of-plane CTE and an in-plane CTE with a difference of at least 1×10−6° C.−1 between the out-of-plane CTE and the in-plane CTE
Implementation Method 2
achieved by sintering a perovskite layer under pressure
Implementation Method 3
The anisotropic CTE cathode minimizes thermal mismatch stresses in SOFCs, reducing the likelihood of failure during temperature changes
Data Source
AI summary
An anisotropic coefficient of thermal expansion (CTE) cathode of a solid oxide fuel cell (SOFC) is formed by placing a layer of perovskite powder between two platens, and sintering the layer while applying pressure to the platens, thereby forming the anisotropic CTE cathode. The perovskite can be lanthanum strontium manganite (LSM).