Stainless Steel Separator for PEMFC Contact Resistance
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Solution Overview
Problem
Conventional stainless steel separators for PEMFCs exhibit high contact resistance due to a non-conductive passive film, which is difficult to address through existing surface treatments, and require additional costly processes to improve corrosion resistance.
Innovation Solution
Stainless steel with a specific composition and surface treatment, including controlled atomic ratios of Cr, Sn, Cl, and F in the passive film, formed through hot-rolling, cold-rolling, and soaking in acid solutions, to reduce contact resistance and enhance corrosion resistance without additional surface processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stainless steel is used for PEMFC separators, then corrosion resistance is improved, but contact resistance increases due to passive film formation
Solution Approach 1:
The patent changes the chemical composition parameters of the stainless steel by adding specific amounts of Sn (0.01-1.0 wt%), Ti (0.01-1.0 wt%), and Nb (0.01-1.0 wt%) elements. These compositional modifications alter the properties of the passive film formed on the steel surface, making it more conductive while maintaining corrosion resistance. The controlled addition of these elements transforms the passive film's electrical characteristics without compromising its protective function.
Solution Approach 2:
The patent creates a composite structure by forming a passive film with specific elemental compositions (enriched in Cr, Sn, Ti, and Nb) on the stainless steel substrate. This passive film acts as a functional layer with different properties than the base metal, combining the corrosion resistance of the stainless steel with the electrical conductivity of the modified passive film, effectively creating a multi-layer composite material system.
2Object-affected harmful factors
If coating processes are applied to reduce contact resistance, then electrical conductivity is improved, but manufacturing cost and time increase
Solution Approach 1:
The patent enables the stainless steel material to self-modify its passive film properties through controlled composition. By incorporating Sn, Ti, and Nb elements during steelmaking, the material automatically forms a conductive passive film during service exposure to oxidizing environments, eliminating the need for external coating processes. This self-organizing property reduces manufacturing steps while achieving the desired electrical conductivity.
Solution Approach 2:
The conductive passive film is formed in advance during the steel manufacturing and heat treatment processes, before the separator is assembled into the fuel cell. The preliminary formation of this functional layer ensures that no additional surface treatment steps are required during separator fabrication, thereby improving manufacturing efficiency and productivity.
3Object-affected harmful factors
If Cr and Fe atomic ratio is controlled in passive film, then contact resistance is reduced, but corrosion resistance in strong acid environment deteriorates
Solution Approach 1:
The patent applies local quality by creating a passive film with non-uniform elemental distribution. The passive film is enriched in Cr for corrosion resistance, while also containing localized concentrations of Sn, Ti, and Nb that provide electrical conductivity. This spatial differentiation of elemental composition allows different regions of the passive film to fulfill different functions: Cr-rich regions provide protection against corrosion, while Sn/Ti/Nb-enriched regions enhance electrical conductivity.
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 achieves a contact resistance of 20 mΩ·cm² or less and improved corrosion resistance, meeting the requirements for long-term performance in a strong acid environment without separate surface treatments.
Implementation Method 1
conventional stainless steel exhibits high resistance due to a passive film formed on a surface
Implementation Method 2
soaking stainless steel containing 17 to 23% Cr in a solution of [HF] ≥ [HNO 3 ]
Data Source
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AI summary
Stainless steel having excellent contact resistance for a PEMFC separator and a method for manufacturing the stainless steel are disclosed. The stainless steel for the Polymer Electrolyte Membrane Fuel Cell (PEMFC) separator according to an embodiment of the present disclosure may include: by weight percent, 0 to 0.02% of C(excluding 0%), 0 to 0.02% of N(excluding 0%), 0 to 0.25% of Si(excluding 0%), 0% to 0.2% of Mn(excluding 0%), 0 to 0.04% of P(excluding 0%), 0 to 0.02% of S(excluding 0%), 25 to 34% of Cr, 0 to 0.5% of Ti(excluding 0%), 0 to 0.5% of Nb(excluding 0%), 0 to 0.6% of Sn(excluding 0%) and the remainder comprising iron (Fe) and other unavoidable impurities, wherein the value of the following formula (1) with respect to the atomic ratio of X and Sn in the region within 3 nm in thickness from a surface of a passive film is 0.001 or more. X/Sn Where X is Cl or F.