Solid Oxide Fuel Cell Coating Porosity Gradient
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Solution Overview
Problem
Conventional solid oxide fuel cells (SOFCs) with Cr-containing current collecting members face issues of Cr diffusion and thermal stress, leading to cathode poisoning and cracking due to temperature variations, which existing coatings and bonding layers fail to adequately address.
Innovation Solution
The fuel cell electricity generation unit is designed with a porosity and thermal expansion coefficient gradient between the coating, bonding layer, and cathode, and the use of spinel oxide for the coating and bonding layer to reduce thermal expansion differences and prevent Cr diffusion, thereby minimizing cracking and maintaining conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of the current collecting member is covered with a coating to prevent Cr diffusion, then Cr poisoning of the cathode is prevented, but thermal stress causes cracks in the coating, bonding layer, or cathode due to temperature variations
Solution Approach 1:
The patent applies parameter changes by optimizing the porosity of the coating and bonding layer. Specifically, the coating is designed with a porosity of 30-70% and the bonding layer with 20-60% porosity. This porosity control modifies the mechanical and thermal properties of these layers, allowing them to better accommodate thermal expansion differences and reduce stress concentration, thereby preventing cracks while maintaining Cr diffusion barrier functionality.
Solution Approach 2:
The patent employs composite materials by creating a multi-layer structure consisting of the coating layer, bonding layer, and cathode. Each layer has specifically controlled porosity to create a gradient structure that manages thermal stress. The composite nature of this layered system, with varying porosity levels, allows for differential thermal expansion accommodation while maintaining structural integrity and Cr diffusion prevention.
2Reliability
If the porosity of the coating is reduced to prevent Cr diffusion, then Cr poisoning is prevented, but thermal stress increases leading to cracks
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the porosity parameter of both the coating (30-70%) and bonding layer (20-60%). This optimized porosity range allows the coating to be sufficiently dense to prevent Cr diffusion while maintaining enough pore space to accommodate thermal expansion and reduce stress concentration, thus preventing cracks under thermal cycling conditions.
Solution Approach 2:
The bonding layer serves as an intermediary between the coating and the cathode. With its controlled porosity (20-60%), it acts as a buffer zone that absorbs thermal stress and facilitates stress transfer, protecting both the coating and cathode from crack propagation while the coating maintains its Cr diffusion barrier function.
3Reliability
If a coating is applied to the current collecting member to prevent Cr diffusion, then cathode poisoning is prevented, but the device complexity increases
Solution Approach 1:
The patent applies multi-functionality by designing the coating and bonding layer to serve multiple functions simultaneously. The coating provides both Cr diffusion barrier and thermal stress management functions through its controlled porosity. The bonding layer provides both bonding functionality and stress buffer capabilities. This multi-functional design reduces the need for additional separate components, thereby managing device complexity while achieving reliable cathode protection.
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 effectively relaxes thermal stress, prevents cracking, and reduces Cr diffusion, enhancing the durability and performance of the fuel cell by maintaining electrical conductivity and preventing cathode poisoning.
Implementation Method 1
Exposure of the current collecting member to a high-temperature atmosphere (e.g., 700° C. to 1,000° C.) during operation of the SOFC may cause a phenomenon called 'Cr diffusion'; i.e., release and diffusion of Cr from the surface of the current collecting member
Implementation Method 2
a porosity of the coating 0.30≤a porosity of the bonding layer<0.70, and a thermal expansion coefficient of a material for forming the coating≤a thermal expansion coefficient of a material for forming the bonding layer
Implementation Method 3
an electrically conductive coating which covers the surface of the current collecting member; and an electrically conductive bonding layer which bonds the cathode to the current collecting member covered with the coating
Data Source
AI summary
A fuel cell electricity generation unit including a unit cell including an electrolyte layer containing a solid oxide, and a cathode and an anode which face each other with the electrolyte layer intervening therebetween; an electrically conductive current collecting member disposed on the cathode side of the unit cell; an electrically conductive coating which covers the surface of the current collecting member; and an electrically conductive bonding layer which bonds the cathode to the current collecting member covered with the coating, wherein the following relationship is satisfied: the porosity of the coating<the porosity of the bonding layer<the porosity of the cathode.