Solid Oxide Fuel Cell Stack Thermal Shock Tolerance
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Solution Overview
Problem
Solid oxide fuel cell stacks are susceptible to damage from temperature fluctuations due to differing coefficients of thermal expansion, thermal conductivity, and strength of materials, leading to limited thermal shock resistance and increased risk of failure during operation.
Innovation Solution
The implementation of a fuel cell assembly with distinct bonding layers between subassemblies, including a first bonding layer at the second electrode, a second bonding layer at the interconnect, and a third bonding layer between subassemblies, which are microstructurally or compositionally distinct, providing compliance and reducing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fuel cells are assembled in stacks with multiple subassemblies, then productivity and power output are improved, but thermal shock resistance and reliability deteriorate due to accumulated mechanical stress from temperature fluctuations
Solution Approach 1:
The fuel cell stack is divided into multiple subassemblies, each comprising a subset of fuel cells grouped together with common interconnects and bonding layers. This segmentation allows individual subassemblies to be manufactured, tested, and assembled separately, reducing the cumulative thermal stress on any single bonding layer while maintaining high overall power output through parallel operation of multiple subassemblies.
Solution Approach 2:
An intermediate bonding layer is introduced between subassemblies that is compositionally distinct from the bonding layers within individual fuel cells. This intermediate layer acts as a stress-absorbing intermediary that accommodates differential thermal expansion between subassemblies, preventing stress propagation throughout the entire stack while maintaining electrical and mechanical integrity.
2Adaptability or versatility
If materials with distinct coefficients of thermal expansion are used to form various components, then functional performance is improved, but mechanical stress from temperature changes increases
Solution Approach 1:
The bonding layers are designed with specific compositional parameters that enable them to undergo controlled dimensional changes in response to temperature fluctuations. By adjusting the chemical composition and microstructure of the bonding layers, they can accommodate differential thermal expansion between components with distinct coefficients of thermal expansion, thereby reducing mechanical stress while maintaining functional performance.
Solution Approach 2:
The bonding layers are formulated as composite materials with tailored properties that bridge the mechanical and thermal properties of adjacent components. These composite bonding layers combine multiple phases or materials that work together to accommodate thermal expansion differences while maintaining strong adhesion and electrical conductivity, thus resolving the conflict between functional performance and mechanical stress resistance.
3Reliability
If multiple bonding layers of distinct compositions are used between subassemblies, then thermal shock resistance is improved, but device complexity increases
Solution Approach 1:
Different bonding layers are assigned specific compositional qualities tailored to their local functional requirements. The intermediate bonding layer between subassemblies has distinct properties optimized for stress accommodation, while bonding layers within individual fuel cells have properties optimized for electrical conductivity and adhesion. This local differentiation of quality allows each bonding layer to perform its specific function efficiently without requiring the entire structure to be overly complex.
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
This configuration enhances the thermal shock resistance of solid oxide fuel cell stacks, allows for inspection and removal of defective subassemblies, and increases manufacturing yield and reliability by mitigating mechanical stress caused by temperature changes.
Implementation Method 1
materials employed to form the various components, including ceramics of differing compositions, exhibit distinct coefficients of thermal expansion, thermal conductivity and strength
Implementation Method 2
A fuel cell is a device that generates electricity by a chemical reaction. Among various fuel cells, solid oxide fuel cells use a hard, ceramic compound metal (e.g., calcium or zirconium) oxide as an electrolyte. Typically, in solid oxide fuel cells, an oxygen gas, such as O2, is reduced to oxygen ions (O2-)
Implementation Method 3
The subcell is operable by oxidation of a fuel directed to one of the first or second electrodes to thereby form at least water
Data Source
Figure 1A
Figure 1B~1D
Figure 2~3
AI summary
A solid oxide fuel cell (SOFC) includes a plurality of subassemblies. Each subassembly includes at least one subcell of a first electrode, a second electrode and an electrolyte between the first and second electrodes. A first bonding layer is at the second electrode and an interconnect layer is at the first bonding layer distal to the electrolyte. A second bonding layer that is compositionally distinct from the first bonding layer is at the interconnect layer, whereby the interconnect partitions the first and second bonding layers. A method of fabricating a fuel cell assembly includes co-firing at least two subassemblies using a third bonding layer that is microstructurally or compositionally distinct from the second bonding layer.