SOFC Interconnect Nickel Mesh Chromium Oxide Suppression
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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 and lifespan.
Innovation Solution
The use of a nickel mesh in contact with the fuel side of the interconnect and a Cr-Ni or Cr-Fe-Ni alloy under the mesh, 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
1Reliability
If chromium alloy interconnects are used in SOFC stacks, then electrical conductivity and structural stability are maintained, but chromium oxide forms on the interconnect surface leading to increased ohmic resistance
Solution Approach 1:
A nickel-containing layer is introduced as an intermediary between the chromium alloy interconnect and the fuel environment. This layer acts as a barrier that prevents direct oxidation of chromium while maintaining electrical conductivity. The nickel layer forms a protective interface that mediates the interaction between the metal substrate and the corrosive fuel atmosphere, thereby preventing chromium oxide formation without compromising the electrical performance of the interconnect.
Solution Approach 2:
The interconnect structure is transformed from a simple chromium alloy into a composite material system consisting of a chromium-based substrate with a nickel-containing surface layer. This composite structure combines the high electrical conductivity and structural stability of chromium with the oxidation resistance of nickel, creating a material that exhibits both properties simultaneously and resolves the contradiction between maintaining conductivity and preventing oxide formation.
2Strength
If chromium alloy interconnects are used in SOFC stacks, then mechanical strength and dimensional stability are maintained at operating temperatures, but chromium diffuses to the cathode causing chromium poisoning
Solution Approach 1:
The nickel-containing layer serves as a diffusion barrier that mediates the interaction between the chromium substrate and the cathode environment. It prevents chromium atoms from diffusing through the interconnect to reach the cathode, while still allowing the interconnect to maintain its mechanical strength through the chromium substrate. The nickel layer acts as a protective intermediary that blocks the harmful diffusion pathway.
3Reliability
If chromium oxide layer grows on interconnect surfaces, then oxidation protection is provided, but ohmic resistance increases over time
Solution Approach 1:
The nickel-containing layer is positioned as an intermediary between the chromium substrate and the oxidizing environment. It provides oxidation protection by forming a stable interface that prevents excessive chromium oxide formation, while simultaneously maintaining low ohmic resistance because nickel itself is an excellent electrical conductor. This mediator layer thus protects against oxidation without introducing significant electrical resistance.
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
chromium in the CrF or CrFeY alloys react with oxygen and form chromia
Implementation Method 2
The chromium oxide layer grows in thickness on the surfaces of the interconnect with time
Implementation Method 3
chromium vapor diffuses through cracks or pores in the coating
Implementation Method 4
chromium ions can diffuse through the lattice of the interconnect coating material into the SOFC cathode via solid state diffusion
Implementation Method 5
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
Implementation Method 6
chromium on the surface of the Cr2O3 layer on the interconnect reacts with water
Implementation Method 7
Formation of a chromium oxide layer is reduced or avoided in locations between the nickel mesh and the fuel side of the interconnect
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.