Iron-Rich SOFC Interconnect Ribs Mitigate 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 performance and longevity of the fuel cell.
Innovation Solution
The use of iron-rich materials and specific metal or metal oxide caps on the interconnects, combined with coatings like manganese cobalt oxide (MCO) spinels, to reduce chromium diffusion and oxidation, thereby minimizing the growth of the chromium oxide layer and preventing cathode poisoning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromium-based alloy interconnects are used in SOFC stacks, then electrical conductivity and structural stability are maintained, but chromium oxide forms on the surface leading to increased ohmic resistance and cathode poisoning
Solution Approach 1:
An iron-rich intermediate layer (containing at least 25 wt. % iron) is introduced between the chromium-based alloy interconnect and the external environment. This intermediate layer acts as a barrier that prevents direct oxidation of chromium and reduces chromium diffusion to the cathode, thereby eliminating the harmful chromium oxide formation while preserving the electrical conductivity and structural stability of the underlying CrF or CrFeY alloy
Solution Approach 2:
The interconnect structure is transformed from a homogeneous chromium-based alloy into a composite structure consisting of multiple layers: the original CrF or CrFeY alloy substrate combined with an iron-rich intermediate layer containing additional elements (4-6 wt. % Fe, 0-1 wt. % Y, and balance Cr). This composite structure leverages the beneficial properties of each layer while mitigating the harmful effects of chromium oxidation
2Duration of action of stationary object
If chromium oxide layer grows on interconnect surface over time, then the interconnect continues to function, but ohmic resistance increases reducing SOFC stack performance
Solution Approach 1:
The iron-rich intermediate layer is applied in advance to the interconnect surface before operation begins. This pre-applied layer creates a protective barrier that prevents the formation of high-resistance chromium oxide during service, thereby maintaining low ohmic resistance throughout the interconnect's service life while preserving its durability
3Strength
If chromium diffuses to the cathode through the interconnect coating, then the interconnect remains structurally intact, but cathode performance degrades due to chromium poisoning
Solution Approach 1:
The iron-rich intermediate layer serves as a diffusion barrier between the chromium-based alloy interconnect and the cathode. It contains chromium diffusion in the form of chromium ions, preventing them from reaching and poisoning the cathode while allowing the interconnect to maintain its structural integrity through the stable CrF or CrFeY alloy substrate
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 reduces the thickness of the chromium oxide layer, decreases ohmic resistance, and prevents chromium poisoning, enhancing the performance and lifespan of the SOFC stack by limiting chromium ion diffusion and oxidation.
Implementation Method 1
chromium ions can diffuse through the lattice of the interconnect coating material into the SOFC cathode via solid state diffusion
Implementation Method 2
chromium in the CrF or CrFeY alloys react with oxygen and form chromia
Implementation Method 3
sintering the interconnect to form a sintered interconnect having iron rich regions having an iron concentration greater than 10% in ribs of the interconnect
Implementation Method 4
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
Implementation Method 5
The chromium oxide hydroxide species transports in vapor form from the interconnect surface to the cathode electrode of the fuel cell where it may deposit in the solid form, Cr2O3
Data Source
AI summary
A method of making an interconnect for a solid oxide fuel cell stack includes providing an iron rich material containing at least 25 wt. % iron into channels of a mold, providing a powder containing 4-6 wt. % Fe, 0-1 wt. % Y and balance Cr into the mold over the iron rich material containing at least 25 wt. % iron, compacting the iron rich material containing at least 25 wt. % iron and the powder comprising 4-6 wt. % Fe, 0-1 wt. % Y and balance Cr in the mold to form the interconnect, and sintering the interconnect to form a sintered interconnect having iron rich regions having an iron concentration greater than 10% in ribs of the interconnect.