Inhibitor for Braze Migration in Solid Oxide Fuel Cells
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Solution Overview
Problem
Silver (Ag) in silver/copper (Ag/Cu) braze alloys migrates in solid oxide fuel cell (SOFC) assemblies during high-temperature operation, causing electrical shorting and internal leakage due to electric potential and spatial surface tension differences, leading to potential failure of the fuel cell stack.
Innovation Solution
Incorporating a mechanical barrier, such as zirconia or glass ceramic, around braze areas, or modifying the electrolyte with insulating dopants like alumina, and adding palladium to the braze alloy to prevent migration, either individually or in combination, to inhibit both mechanically-driven and electrically-driven braze migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ag/Cu braze alloys are used for sealing in SOFC assemblies, then electrical conductivity and sealing performance are improved, but braze migration occurs causing electrical shorting and internal leakage
Solution Approach 1:
A mechanical barrier layer composed of zirconia or glass ceramic silicate is introduced between the Ag/Cu braze alloy and the chemically/electrically active regions. This intermediary layer prevents direct contact and migration of the braze material into active regions, blocking the harmful effect while maintaining the sealing function of the braze.
Solution Approach 2:
The harmful migrating component (Ag) is effectively isolated from the active regions by removing its migration path through the introduction of a barrier layer. The braze material remains in place at the seal margin, separated from regions where it would cause electrical shorting or internal leakage.
2Reliability
If Ag/Cu braze alloys are used to provide electrical conductivity, then electrical connection is improved, but electrical potential-driven migration occurs leading to shorting
Solution Approach 1:
The mechanical barrier layer acts as an electrical insulator that prevents the braze material from migrating into electrically active regions. This intermediary structure maintains the electrical connection function of the braze at the seal margin while blocking its migration path that would otherwise cause electrical shorting.
Solution Approach 2:
The barrier layer is applied locally around the braze areas where migration is most likely to occur. This localized application provides electrical insulation precisely where needed to prevent shorting, while maintaining electrical conductivity in other necessary regions of the fuel cell assembly.
3Reliability
If mechanical barrier materials are added around braze areas, then braze migration is prevented, but device complexity increases
Solution Approach 1:
The mechanical barrier is implemented as a thin film or coating layer of zirconia or glass ceramic silicate applied around the braze areas. This thin-film approach provides effective migration prevention while minimizing the increase in device complexity and maintaining a relatively simple assembly structure.
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 proposed solution effectively prevents braze migration, ensuring the stability and longevity of SOFC assemblies by reducing the mobility of Ag/Cu braze at operating temperatures, thereby preventing electrical shorting and leakage.
Implementation Method 1
a mechanical barrier that can be printed or dispensed onto one or more SOFC stack elements around the braze areas to prevent mechanically-driven migration
Implementation Method 2
an electrically insulating feature in the electrolyte or interlayer over the electrolyte layer in the seal margins to prevent electrical potential-driven migration
Implementation Method 3
chemical modification of the braze itself as by addition of an alloying metal such as palladium. The inclusion of about 15% palladium (Pd) in the braze significantly reduces the mobility of an Ag/Cu braze at SOFC operating temperatures
Data Source
AI summary
During manufacture of an SOFC assembly, an inhibitor is included to prevent migration of silver braze during subsequent use of the SOFC assembly. The inhibitor may take any of several forms, either individually or in combination. Inhibitors comprehended by the present invention include, but are not limited to: a) a mechanical barrier that can be printed or dispensed onto one or more SOFC stack elements around the braze areas to prevent mechanically-driven migration; b) an electrically insulating feature in the electrolyte or interlayer over the electrolyte layer in the seal margins to prevent electrical potential-driven migration; and 3) chemical modification of the braze itself as by addition of an alloying metal such as palladium.