SOFC Interconnect Rib Tip Iron Layer Reduces Chromium Poisoning
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Solution Overview
Problem
Solid oxide fuel cell (SOFC) stacks experience degradation due to chromium oxide formation on metallic interconnects, leading to increased ohmic resistance and chromium poisoning of the cathode, which reduces performance.
Innovation Solution
A method of forming interconnects with a contact layer on the tips of ribs, comprising a conductive metal oxide and glass material with a glass transition temperature of 900°C or less, which is applied only over the tips of the ribs, and an iron layer with a higher concentration than the remainder of the interconnect, to prevent chromium oxide growth and improve electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chromium-based interconnect material is used, then mechanical strength and dimensional stability are maintained, but chromia formation increases ohmic resistance and causes chromium poisoning
Solution Approach 1:
The patent applies a contact layer with specific composition (containing at least 50 at% Cr, 5 at% Fe, and 5 at% Al) only at the rib tip regions where electrical contact with the cathode is required. This local modification provides low contact resistance and prevents chromium poisoning at the critical interface, while the bulk interconnect material maintains its mechanical strength and structural integrity.
Solution Approach 2:
The patent creates a composite structure consisting of the chromium-based interconnect bulk material combined with a specially formulated contact layer. The contact layer acts as an intermediate material that provides both electrical conductivity and resistance to chromium poisoning, while the bulk material provides mechanical support. This composite approach resolves the contradiction between strength and electrical conductivity.
2Stability of the object's composition
If chromium-based interconnect material is used, then structural stability is maintained, but chromium diffusion poisons the cathode
Solution Approach 1:
The contact layer serves as an intermediary barrier between the chromium-based interconnect bulk and the cathode. This intermediate layer prevents direct contact between chromium ions and the cathode, thereby blocking the chromium poisoning mechanism while allowing the bulk interconnect to maintain its dimensional stability and structural properties.
Solution Approach 2:
The harmful chromium diffusion is prevented locally at the cathode interface through the contact layer, while the bulk interconnect material retains its chromium composition for structural stability. The Al-containing contact layer specifically targets the interface region where chromium poisoning occurs, without altering the bulk material properties.
3Ease of manufacture
If conventional interconnect material is used, then manufacturing simplicity is maintained, but area-specific resistance degrades over time
Solution Approach 1:
The contact layer is applied to the rib tips during the interconnect manufacturing process, before the fuel cell stack is assembled. This preliminary action ensures that the low-resistance contact interface is already in place, preventing future degradation of area-specific resistance. The contact layer can be applied through various methods including co-sintering, screen printing, or thermal spray, integrating the protective function into the manufacturing workflow.
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 solution effectively reduces area-specific resistance degradation and chromium poisoning, enhancing the longevity and performance of the SOFC stack by limiting chromium oxide formation and improving contact resistance.
Implementation Method 1
a glass material having a glass transition temperature of 900° C. or less
Implementation Method 2
chromium in the CrFe or CrFeY alloys react with oxygen and form chromia
Implementation Method 3
sintering the interconnect, such that the iron forms an contact layer on the tips of the ribs
Data Source
AI summary
A method of making an interconnect for a solid oxide fuel cell stack includes contacting an interconnect powder located in a die cavity with iron, the interconnect powder including a chromium and iron, compressing the interconnect powder to form an interconnect having ribs and fuel channels on a first side of the interconnect, such that the iron is disposed on tips of the ribs; and sintering the interconnect, such that the iron forms an contact layer on the tips of the ribs having a higher iron concentration than a remainder of the interconnect. A glass containing cathode contact layer having a glass transition temperature of 900° C. or less may be located over the rib tips on the oxidant side of the interconnect.