Ferritic Stainless Steel SOFC Interconnects for Oxidation Resistance
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Solution Overview
Problem
Current solid oxide fuel cell (SOFC) interconnects face challenges such as oxidation leading to degradation of electrical properties, chromium migration causing cathode poisoning, and the need for high-temperature treatments or expensive superalloys to achieve desired properties, while existing metallic interconnects suffer from increased resistance and inefficient operation due to oxide formation.
Innovation Solution
Development of interconnects formed from ferritic stainless steel with specific alloy compositions that develop manganese-chromate spinel and aluminum-rich oxide scales, which reduce chromium migration and maintain electrical conductivity, along with selective electropolishing to control scale formation and prevent oxidation on critical surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional metallic interconnects are used in SOFCs, then electrical conductivity is initially good, but oxidation occurs leading to increased resistance and degradation of electrical properties
Solution Approach 1:
A chromium-rich oxide scale layer is introduced as an intermediary protective barrier between the metallic interconnect and the oxidizing atmosphere. This scale forms in situ during operation and acts as a mediator that prevents further oxidation of the underlying metal while maintaining electrical conductivity through its inherent conductive properties.
Solution Approach 2:
The interconnect material composition is modified by adding specific alloying elements (such as aluminum, silicon, or rare earth elements) to change the oxidation behavior. These compositional parameter changes enable the formation of a stable, conductive chromium-rich oxide scale rather than non-conductive oxides, thus maintaining electrical conductivity while providing oxidation protection.
2Reliability
If chromium-containing alloys are used to form protective oxide scales, then oxidation resistance is improved, but chromium migration occurs causing cathode poisoning
Solution Approach 1:
The alloy composition parameters are optimized by controlling the chromium content and adding specific elements (such as aluminum or silicon) that modify the oxide scale structure. This compositional adjustment creates a more stable chromium oxide scale that reduces chromium volatility and migration while maintaining oxidation protection.
Solution Approach 2:
The interconnect material is designed as a composite alloy system combining chromium with other elements (aluminum, silicon, rare earth elements) that work synergistically. The chromium provides oxidation resistance through scale formation, while the additional elements stabilize the scale structure and reduce chromium migration, creating a multi-functional composite material system.
3Reliability
If high-temperature treatments are applied to achieve desired scale formation, then oxidation resistance is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The interconnect material is designed to self-form the protective chromium-rich oxide scale during normal SOFC operation without requiring external high-temperature treatment processes. The material's compositional design enables automatic scale formation and stabilization under operating conditions, eliminating the need for separate manufacturing steps and reducing overall process complexity.
Solution Approach 2:
The alloy composition is pre-designed during material fabrication to contain the necessary elements in optimal ratios that will automatically form the protective scale under operating conditions. This preliminary compositional preparation eliminates the need for subsequent high-temperature treatment steps, as the scale-forming capability is built into the material itself during initial manufacturing.
4Reliability
If expensive superalloys are used to achieve desired properties, then oxidation resistance and electrical conductivity are improved, but material cost increases
Solution Approach 1:
The alloy composition parameters are optimized to achieve the desired performance using more cost-effective base materials. By adjusting the ratios of chromium, aluminum, silicon, and rare earth elements within specific ranges, the material achieves equivalent or superior oxidation resistance and electrical conductivity to expensive superalloys, but at a lower material cost through careful compositional control rather than using premium alloying elements in high quantities.
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 chromium migration, maintains electrical conductivity, and prevents oxidation on critical surfaces, thereby enhancing the operational efficiency and longevity of SOFCs without requiring high-temperature treatments or expensive materials.
Implementation Method 1
when subjected to an oxidizing atmosphere at an elevated temperature develops a scale comprising a manganese-chromate spinel on at least a portion of a surface thereof
Implementation Method 2
develops an aluminum-rich oxide scale on at least a portion of a surface thereof, the aluminum-rich oxide scale comprising iron and chromium and having a hematite structure
Implementation Method 3
selective electropolishing to control scale formation and prevent oxidation on critical surfaces
Implementation Method 4
maintains electrical conductivity
Implementation Method 5
reduce chromium migration
Data Source
AI summary
Various embodiments relate to interconnects for solid oxide fuel cells (“SOFCs”) comprising ferritic stainless steel and having at least one via that when subjected to an oxidizing atmosphere at an elevated temperature develops a scale comprising a manganese-chromate spinel on at least a portion of a surface thereof, and at least one gas flow channel that when subjected to an oxidizing atmosphere at an elevated temperature develops an aluminum-rich oxide scale on at least a portion of a surface thereof. Other embodiments relate to interconnects comprising a ferritic stainless steel and having a fuel side comprising metallic material that resists oxidation during operation of the SOFCs, and optionally include a nickel-base superalloy on the oxidant side thereof. Still other embodiments relate to ferritic stainless steels adapted for use as interconnects comprising ≦0.1 weight percent aluminum and/or silicon, and >1 up to 2 weight percent manganese. Methods of making interconnects are also disclosed.