Stainless steel for fuel cell separator plate and manufacturing method therefor

Patent metadata

Field	Value
Publication number	US-2018219201-A1
Application number	US-201615747973-A
Country	US
Kind code	A1
Filing date	Jul 29, 2016
Priority date	Sep 22, 2015
Publication date	Aug 2, 2018
Grant date	—

Abstract

Stainless steel for a fuel cell separator plate and a manufacturing method therefor are disclosed. The stainless steel for a fuel cell separator plate, according to one embodiment of the present invention, comprises: a stainless base material; and a passive film formed on the stainless base material, wherein a Cr/Fe atomic weight ratio in a 1 nm or less thickness region of the stainless base material, which is adjacent to an interface between the stainless and the passive film, is 0.45 or more. Therefore, by modifying the surface of the stainless steel for a fuel cell separator plate, a low interface contact resistance and a good corrosion resistance can be obtained, and a separate additional process such as precious metal coating can be removed, such that manufacturing costs are reduced and productivity can be improved.

First claim

1 . A stainless steel for a fuel cell separator plate comprising a stainless base material and a passive film formed on the stainless base material,
wherein a region of the stainless base material having a thickness of 1 nm or less, which is adjacent to an interface between the stainless base material and the passive film, has a Cr/Fe atomic weight ratio of 0.45 or more.

2 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the stainless steel for a fuel cell separator plate comprises C at greater than 0 to 0.02 wt %, N at greater than 0 to 0.02 wt %, Si at greater than 0 to 0.4 wt %, Mn at greater than 0 to 0.2 wt %, P at greater than 0 to 0.04 wt %, S at greater than 0 to 0.02 wt %, Cr at 25 to 34 wt %, Mo at 0 to less than 0.1 wt %, Cu at 0 to 1 wt %, Ni at 0 to less than 0.2 wt %, Ti at greater than 0 to 0.5 wt %, Nb at greater than 0 to 0.5 wt %, and the balance of Fe and other inevitable impurities.

3 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the Cr/Fe atomic weight ratio at the interface between the stainless steel base material and the passive film is greater than or equal to 0.65.

4 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the Cr/Fe atomic weight ratio in the passive film is greater than or equal to 1.0.

5 . The stainless steel for a fuel cell separator plate of claim 1 , wherein a content of Si atoms in the passive film is less than or equal to 0.1 at %.

6 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the passive film has a thickness of 3.5 nm or less (excluding 0).

7 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the passive film has an interfacial contact resistance of 10 mΩcm 2 (100 N/cm 2 ) or less.

8 . The stainless steel for a fuel cell separator plate of claim 1 , wherein the passive film has a corrosion potential of 0.3 V SCE or more.

9 . A method of manufacturing a stainless steel for a fuel cell separator plate, the method comprising:
subjecting a stainless steel sheet to bright annealing to form a first passive film on a stainless base material (a heat treatment step); and modifying the first passive film to form a second passive film on the stainless base material (a modification step), wherein a region of the stainless base material having a thickness of 1 nm or less, which is adjacent to an interface between the stainless base material and the passive film, has a Cr/Fe atomic weight ratio of 0.45 or more.

10 . The method of claim 9 , wherein the stainless steel sheet comprises C at greater than 0 to 0.02 wt %, N at greater than 0 to 0.02 wt %, Si at greater than 0 to 0.4 wt %, Mn at greater than 0 to 0.2 wt %, P at greater than 0 to 0.04 wt %, S at greater than 0 to 0.02 wt %, Cr at 25 to 34 wt %, Mo at 0 to less than 0.1 wt %, Cu at 0 to 1 wt %, Ni at 0 to less than 0.2 wt %, Ti at greater than 0 to 0.5 wt %, Nb at greater than 0 to 0.5 wt %, and the balance of Fe and other inevitable impurities.

11 . The method of claim 9 , wherein the modification step comprises:
electrolytically treating the first passive film at a first current density in a sulfuric acid solution (a first film modification step); electrolytically treating the first passive film at a second current density, which is less than or equal to the first current density, in the sulfuric acid solution (a second film modification step); and dipping the first passive film in a mixed acid solution including nitric acid and hydrofluoric acid (a third film modification step), wherein the first film modification step and the second film modification step are sequentially performed.

12 . The method of claim 11 , wherein, in the first film modification step, a potential of the stainless steel sheet corresponding to the first current density satisfies the following Expressions (1) and (2).
E anode ≥1.0  Expression (1)
| E anode |+|E cathode |≥2.0  Expression (2)

13 . The method of claim 11 , wherein, in first film modification step and the second film modification step, the sulfuric acid solution has a concentration of 50 to 300 g/L, and the sulfuric acid solution has a temperature of 40 to 80° C.

14 . The method of claim 11 , wherein, in the third film modification step, a concentration of the nitric acid in the mixed acid solution is in a range of 100 to 200 g/L, a concentration of the hydrofluoric acid is less than or equal to 70 g/L, and a temperature of the mixed acid solution is in a range of 40 to 60° C.

15 . The method of claim 11 , wherein, in the first film modification step and the second film modification step, the sulfuric acid solution is allowed to flow in an electrolytic bath containing the sulfuric acid solution to remove bubbles generated on surfaces of an electrode and the stainless steel sheet.

16 . The method of claim 9 , wherein the first passive film has an interfacial contact resistance of greater than 10 mΩcm 2 (100 N/cm 2 ), and the second passive film has an interfacial contact resistance of 10 mΩcm 2 (100 N/cm 2 ) or less.

17 . The method of claim 9 , wherein the Cr/Fe atomic weight ratio at the interface between the stainless steel base material and the second passive film is greater than or equal to 0.65.

18 . The method of claim 9 , wherein the Cr/Fe atomic weight ratio in the second passive film is greater than or equal to 1.0.

19 . The method of claim 9 , wherein the second passive film has a thickness of 3.5 nm or less (excluding 0).

Assignees

• Posco

Inventors

• Kim Kwang Min
• Kim Jong Hee
• Jo Ki Hoon
• Seo Bo Sung

Classifications

• H01M8/1018 Primary

  Polymeric electrolyte materials · CPC title

• H01M8/1004

  characterised by membrane-electrode assemblies [MEA] (H01M8/12 takes precedence) · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/44

  with molybdenum or tungsten · CPC title

• C22C38/48

  with niobium or tantalum · CPC title