SOFC Interconnect Contact Layer Blocks 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 affects the stack's performance and longevity.
Innovation Solution
The use of a nickel mesh and specific alloy compositions, such as Cr—Ni or Cr—Fe—Ni, on the fuel side of the interconnect, combined with coatings like lanthanum strontium manganese oxide (LSM) or manganese cobalt oxide (MCO) spinels, to reduce chromium oxide formation and diffusion, thereby suppressing the growth of the native chromium oxide layer and preventing chromium poisoning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chromium alloy interconnect is used, then strength and dimensional stability are maintained, but chromium oxide forms causing increased ohmic resistance
Solution Approach 1:
A metal or metal oxide contact layer is introduced as an intermediary between the chromium alloy interconnect and the nickel mesh. This contact layer prevents direct contact between chromium and oxygen, blocking chromia formation at the critical interface while maintaining electrical conductivity and mechanical strength of the interconnect structure.
Solution Approach 2:
The interconnect structure is transformed into a composite system consisting of multiple layers: chromium alloy substrate, metal/metal oxide contact layer, and nickel mesh. This composite structure combines the strength of chromium alloy with the protective properties of the contact layer that prevents oxide formation.
2Stability of the object's composition
If chromium alloy interconnect is used, then structural stability is maintained, but chromium diffuses poisoning the cathode
Solution Approach 1:
The metal or metal oxide contact layer serves as a diffusion barrier, mediating between the chromium alloy interconnect and the nickel mesh/cathode. It blocks chromium ion diffusion to the cathode while allowing oxygen to pass through for interconnect protection, preventing chromium poisoning of the cathode.
Solution Approach 2:
The harmful chromium diffusion pathway is extracted or removed from the system by introducing the contact layer that selectively blocks chromium ions while permitting oxygen transport, effectively separating the protective oxidation function from the harmful chromium diffusion.
3Object-affected harmful factors
If nickel mesh is placed in contact with fuel side, then chromium oxide formation is reduced, but contact layer is required
Solution Approach 1:
A thin metal or metal oxide contact layer is introduced as an intermediary between the nickel mesh and the chromium alloy interconnect. This contact layer is necessary because nickel directly contacting chromium would form high-resistance intermetallic compounds, while the contact layer enables beneficial chromium oxide formation suppression without compromising electrical conductivity.
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 approach effectively limits chromium ion diffusion and reduces the formation of high-resistance chromium oxide layers, enhancing the electrical conductivity and longevity of the SOFC stack by minimizing ohmic resistance and cathode degradation.
Implementation Method 1
A metal or metal oxide contact layer is coated over ribs on the fuel side of the interconnect beneath the nickel mesh. Formation of a chromium oxide layer is reduced or avoided in locations between the nickel mesh and the fuel side of the interconnect.
Implementation Method 2
The metallic interconnects are commonly composed of a Cr based alloy such as an alloy known as CrF which has a composition of 95 wt % Cr-5 wt % Fe or Cr—Fe—Y having a 94 wt % Cr-5 wt % Fe-1 wt % Y composition.
Implementation Method 3
during operation of the SOFCs, chromium in the CrF or CrFeY alloys react with oxygen and form chromia, resulting in degradation of the SOFC stack
Implementation Method 4
At SOFC operating temperatures, chromium vapor diffuses through cracks or pores in the coating and chromium ions can diffuse through the lattice of the interconnect coating material into the SOFC cathode via solid state diffusion.
Implementation Method 5
At SOFC operating temperatures and in the presence of humid air (cathode side), chromium on the surface of the Cr2O3 layer on the interconnect reacts with water and evaporates in the form of the gaseous species chromium oxide hydroxide, CrO2(OH)2.
Data Source
AI summary
A method of making an interconnect for a solid oxide fuel cell stack includes providing a chromium alloy interconnect and providing a nickel mesh in contact with a fuel side of the interconnect. Formation of a chromium oxide layer is reduced or avoided in locations between the nickel mesh and the fuel side of the interconnect. A Cr—Ni alloy or a Cr—Fe—Ni alloy is located at least in the fuel side of the interconnect under the nickel mesh.