Ferritic Stainless Steel Separator for Polymer Fuel Cells
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Solution Overview
Problem
Stainless steel fuel cell separators face challenges in maintaining low interfacial contact resistance and corrosion resistance under varying surface roughness conditions and acidic environments, with existing methods requiring strict control of surface roughness and additional elements that increase production costs and complexity.
Innovation Solution
A stainless steel composition with specific element limits and a two-step surface reforming process involving bright-annealing, pickling in sulfuric acid, and passivation in nitric and fluorine acid solutions to control the thickness and composition of the passive film, ensuring low contact resistance and corrosion resistance across different surface roughness conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface roughness of stainless steel separator is regulated to decrease contact resistance, then the interfacial contact resistance is reduced, but the manufacturing precision and production cost increase due to strict control requirements
Solution Approach 1:
The invention changes the chemical composition parameters of the stainless steel by optimizing Cr content (16-45 wt%) and Mo content (0.1-3.0 wt%), which fundamentally alters the properties of the passive film formed on the surface. This allows the passive film to have low contact resistance inherently, reducing the need for strict surface roughness control while achieving reliable electrical contact performance
Solution Approach 2:
The invention performs preliminary action by adding specific alloying elements (Cr and Mo) during steel manufacturing to pre-form a passive film with desirable properties. This preliminary chemical preparation ensures that subsequent surface treatments and assembly processes will achieve low contact resistance without requiring extremely precise surface roughness control
2Reliability
If additional elements such as Ag, C, and B are added to decrease contact resistance, then the interfacial contact resistance is reduced, but the device complexity and production cost increase
Solution Approach 1:
The invention extracts and eliminates unnecessary alloying elements from the stainless steel composition. By removing elements like Ag, C, and B that were previously added to reduce contact resistance, the invention simplifies the alloy composition while maintaining low contact resistance through the optimized Cr and Mo content that control passive film properties
Solution Approach 2:
The invention changes the compositional parameters by focusing on Cr (16-45 wt%) and Mo (0.1-3.0 wt%) content optimization. This parameter change approach achieves low contact resistance through controlled passive film formation rather than through complex multi-element additions, thereby reducing device complexity
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 process achieves stable low interfacial contact resistance and excellent corrosion resistance, reducing production costs and ensuring long-term performance of the stainless steel fuel cell separators.
Implementation Method 1
removing a first passive film formed on the surface of the stainless steel by pickling the stainless steel in a sulfuric acid solution
Implementation Method 2
forming a second passive film by performing a passivation treatment on the stainless steel in a mixture of a nitric acid and a fluorine acid
Implementation Method 3
forming a second passive film by performing a passivation treatment on the stainless steel
Data Source
AI summary
There are provided a ferrite stainless steel for a polymer fuel cell separator having excellent corrosion resistance and interfacial contact resistance under an operating environment of a polymer fuel cell, and a preparation method of the stainless steel. A stainless steel includes C: 0.02 wt % or less, N: 0.02 wt % or less, Si: 0.4 wt % or less, Mn: 0.2 wt % or less, P: 0.04 wt % or less, S: 0.02 wt % or less, Cr: 25.0 to 32.0 wt %, Cu: 0 to 2.0 wt %, Ni: 0.8 wt % or less, Ti: 0.5 wt % or less, Nb: 0.5 wt % or less, waste Fe and inevitably contained elements. A preparation method of the stainless steel having a second passive film formed on a surface thereof includes forming a first passive film on the surface of the stainless steel by bright-annealing or annealing-pickling the stainless steel; removing the first passive film by pickling the stainless steel in a 10 to 20 wt % sulfuric acid solution at a temperature of 50 to 75° C. for a predetermined time; water-washing the stainless steel; and forming the second passive film by performing a passivation treatment on the stainless steel in the mixture of a 10 to 20 wt % nitric acid and a 1 to 10 wt % fluorine acid at a temperature of 40 to 60° C. for the predetermined time. Accordingly, it is possible to prepare a stainless steel having reduced elution resistance and excellent corrosion resistance and to produce a stainless steel for a polymer fuel cell separator, which has low interfacial contact resistance and excellent long-term performance even under a fuel cell operating condition of 60 to 150° C. and various surface roughness conditions.