Stainless Steel Fuel Cell Separator with Cr-Rich Passive Film
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Solution Overview
Problem
Metallic bipolar plates in fuel cells face corrosion issues leading to contamination and performance deterioration, with existing materials lacking sufficient corrosion resistance and electrical conductivity, especially under high temperature-high humidity conditions.
Innovation Solution
A method for manufacturing a stainless steel separator involving surface modification with a Cr-rich passive film and a thin coating layer of metal nitride, carbide, or boride to enhance corrosion resistance and electrical conductivity, using a solution of sulfuric acid and nitric acid, followed by heat-treatment to maintain performance over long durations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metallic bipolar plates are used in fuel cells, then manufacturing cost and weight are reduced, but corrosion resistance deteriorates leading to contamination and performance deterioration
Solution Approach 1:
The patent applies composite materials by combining stainless steel substrate with multiple coating layers (chromium oxide layer and protective coating layer). This composite structure maintains the mechanical strength and electrical conductivity of metallic materials while providing superior corrosion resistance through the protective chromium oxide and spinel layers, thereby resolving the contradiction between ease of manufacture and reliability.
2Strength
If stainless steel is used for bipolar plates, then strength and air-tightness are improved, but electrical conductivity deteriorates due to oxide film formation
Solution Approach 1:
The patent applies local quality by creating a chromium-rich passive film specifically on the surface of the stainless steel through selective dissolution. This localized chromium enrichment forms a thin, electrically conductive oxide layer that maintains electrical conductivity while preserving the bulk strength of the stainless steel material.
Solution Approach 2:
The patent applies parameter changes by controlling the (Cr+Ni)/Fe ratio in the superficial layer to be 1 or more through surface modification. This parameter adjustment optimizes both corrosion resistance and electrical conductivity by enhancing chromium content at the surface, which forms a more conductive oxide film while maintaining the structural integrity of the stainless steel.
3Reliability
If surface modification with Cr-rich passive film is applied, then corrosion resistance is improved, but manufacturing process complexity increases
Solution Approach 1:
The patent applies self-service through selective dissolution where the stainless steel surface automatically enriches in chromium and nickel when exposed to the acid solution, forming the protective Cr-rich passive film without requiring external chromium deposition equipment. This self-organizing surface modification process simplifies manufacturing by eliminating complex coating equipment while achieving superior corrosion 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
The method provides a stainless steel separator with superior corrosion resistance and electrical conductivity that meets DOE standards both initially and after extended exposure to harsh fuel cell conditions, ensuring long-term durability and reduced manufacturing costs.
Implementation Method 1
forming on a surface of the stainless steel sheet (200) a Cr-rich passive film (210) by increasing the relative amount of Cr in a superficial layer of the stainless steel sheet (200) by decreasing an amount of Fe in the superficial layer of the stainless steel sheet (200)
Implementation Method 2
heat-treating the surface-modified stainless steel sheet at 100° C to 300° C under vacuum, in air or in an inert gas atmosphere
Implementation Method 3
forming a coating layer (220), wherein the coating layer (220) is formed in a film shape having a thickness of 30 nm to 300 nm, on the surface of the surface-modified stainless steel sheet (200)
Data Source
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AI summary
A stainless steel separator for fuel cells and a method of manufacturing the same are disclosed. The method includes preparing a stainless steel sheet as a matrix, performing surface modification on a surface of the stainless steel sheet to form a Cr-rich passive film having a comparatively increased amount of Cr in a superficial layer of the stainless steel sheet by decreasing an amount of Fe in the superficial layer of the stainless steel sheet, and forming a coating layer on the surface of the surface-modified stainless steel sheet. The coating layer is one selected from a metal nitride layer (MNx), a metal/metal nitride layer (M/MNx), a metal carbide layer (MCy), and a metal boride layer (MBz).