# US 11,993,852 B2 · Method for manufacturing stainless steel for polymer fuel cell separator having excellent contact resistance

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- Number: US 11,993,852 B2
- Document ID: US11993852B2
- Status: Granted
- Kind: B2
- Application number: 17/253,866
- Filed: 2018-06-20
- Published: 2021-09-02
- Granted: 2024-05-28
- Earliest claimed: 2018-06-20
- Assignees: Posco
- Applicants: Posco
- Inventors: Jong Hee Kim; Kwang-Min Kim; Bo-Sung Seo
- Web page: https://patentgrep.com/patent/US11993852B2

## CPC

- C23C 22/06: using aqueous acidic solutions with pH less than 6
- C23C 22/34: containing fluorides or complex fluorides
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/02: containing silicon
- C22C 38/20: with copper
- C22C 38/22: with molybdenum or tungsten
- C22C 38/24: with vanadium
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- C23C 22/50: Treatment of iron or alloys based thereon
- C23C 22/78: Pretreatment of the material to be coated
- C25F 1/06: Iron or steel
- H01M 8/021: Alloys based on iron
- H01M 8/0228: in the form of layered or coated products
- H01M 8/1004: characterised by membrane-electrode assemblies [MEA] (H01M8/12 takes precedence)
- H01M 8/1007: with both reactants being gaseous or vaporised (H01M8/12 takes precedence)
- H01M 2008/1095: {Fuel cells with polymeric electrolytes}
- Y02E 60/50: Fuel cells
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C25F: PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

Disclosed is a method of manufacturing a stainless steel with excellent contact resistance for a polymer fuel cell separator. The method of manufacturing a stainless steel with excellent contact resistance for a polymer fuel cell separator according to an embodiment of the present disclosure includes: electrolyzing to remove a first passivation film formed on a cold-rolled thin sheet of a stainless steel comprising, in percent (%) by weight of the entire composition, C: greater than 0 to 0.1%, N: greater than 0 to 0.02%, Si: greater than 0 to 0.25%, Mn: greater than 0 to 0.2%, P: greater than 0 to 0.04%, S: greater than 0 to 0.02%, Cr: 22 to 34%, Ti: greater than 0 to 0.5%, Nb: greater than 0 to 0.5%, the remainder of iron (Fe) and other inevitable impurities; and immersing in a mixed acid solution of nitric acid and hydrofluoric acid to form a second passivation film on the stainless cold-rolled thin sheet.

## Claims

### Claim 1

A method of manufacturing a stainless steel for a polymer fuel cell separator, the method comprising:
electrolyzing to remove a first passivation film formed on a cold-rolled sheet of a stainless steel comprising, in percent (%) by weight of the entire composition, C: greater than 0 to 0.1%, N: greater than 0 to 0.02%, Si: greater than 0 to 0.25%, Mn: greater than 0 to 0.2%, P: greater than 0 to 0.04%, S: greater than 0 to 0.02%, Cr: 29.7 to 30.1%, Ti: greater than 0 to 0.5%, Nb: greater than 0 to 0.5%, the remainder of iron (Fe) and inevitable impurities; and
immersing in an acid solution to form a second passivation film on the stainless cold-rolled sheet,
wherein the electrolyzing is performed in 5 to 30% by weight of sulfuric acid solution at 40 to 80° C. and a cathode applied current density (Ic) is 4 to 15 A/dm2,
the immersing in the acid solution is performed in 10 to 15% by weight of nitric acid at 40 to 60° C.,
the acid solution does not comprise hydrofluoric acid,
a contact resistance of the second passivation film is 18.2 mΩcm2 or less, and
no surface rust is found on a surface of the polymer fuel cell separator after performing a static potential endurance test at 0.6V for 300 hours.

### Claim 2 (depends on 1)

The method of claim 1, wherein the cold-rolled sheet of the stainless steel further comprises any one or more selected from the group consisting of Cu: greater than 0 to 0.6%, V: greater than 0 to 0.6%, and Mo: 0.05 to 2.5%.