Stainless steel for fuel cell separator with excellent surface hydrophilicity and electrical conductivity, and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-2023420697-A1
Application number	US-202118038389-A
Country	US
Kind code	A1
Filing date	Nov 18, 2021
Priority date	Nov 24, 2020
Publication date	Dec 28, 2023
Grant date	—

Abstract

Disclosed is a stainless steel for a fuel cell separator having excellent surface hydrophilicity and electrical conductivity. According to an embodiment of a stainless steel for a fuel cell separator having excellent surface hydrophilicity and electrical conductivity, the surface oxide element ratio (1) value below may be 0.2 or more and the contact angle may be 80° or less as measured for the surface of a stainless steel containing 15 wt % or more of Cr by X-ray angle-resolved photoemission spectroscopy using an Al-Kα X-ray source under the condition where a take-off angle of photoelectrons is from 120 to 85°.

S
⁢
um
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of
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atomic
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concentrations
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(

at
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%

)

of
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Cr
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in
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Cr
⁢

oxides
⁢

and
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Cr
⁢

hydroxides

Sum
⁢

of
⁢

atomic
⁢

concentrations
⁢

(

at
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%

)

⁢

of

metal
⁢

elements
⁢

in
⁢

entire
⁢

oxides
⁢

and
⁢

hydroxides

(
1
)

The Cr oxide represents Cr 3 O 4 , Cr 2 O 3 , CrO 2 , or CrO 3 , and the Cr hydroxide represents CrOOH, Cr(OH) 2 , or Cr(OH) 3 . The entire oxides and hydroxides include the Cr oxide, the Cr hydroxide, an Fe oxide, an Fe hydroxide, and a metal oxide (MO), wherein the metal oxide (MO) includes a mixed oxide, M represents an alloying element contained in a matrix other than Cr and Fe, or a combination thereof, and O represents oxygen.

First claim

1 . A stainless steel for a fuel cell separator having excellent surface hydrophilicity and electrical conductivity,
wherein a value of a surface oxide element ratio (1) below is 0.2 or more, when measured on the surface of a stainless steel containing 15 wt % or more of Cr by X-ray angle-resolved photoemission spectroscopy using an Al-Kα X-ray source under the condition where a take-off angle of photoelectrons is from 12° to 85°, and a contact angle is 800 or less:

S
⁢
um
⁢

of
⁢

atomic
⁢

concentrations
⁢

(

at
⁢

%

)

of
⁢

Cr
⁢

in
⁢

Cr
⁢

oxides
⁢

and
⁢

Cr
⁢

hydroxides

Sum
⁢

of
⁢

atomic
⁢

concentrations
⁢

(

at
⁢

%

)

⁢

of

metal
⁢

elements
⁢

in
⁢

entire
⁢

oxides
⁢

and
⁢

hydroxides

(
1
)

wherein the Cr oxide represents Cr 3 O 4 , Cr 2 O 3 , CrO 2 , or CrO 3 , and the Cr hydroxide represents CrOOH, Cr(OH) 2 , or Cr(OH) 3 ; and
the entire oxides and hydroxides comprise the Cr oxide, the Cr hydroxide, an Fe oxide, an Fe hydroxide, and a metal oxide (MO), wherein the metal oxide (MO) includes a mixed oxide, M represents an alloying element contained in a matrix other than Cr and Fe or a combination thereof, and O represents oxygen.

2 . The stainless steel for a fuel cell separator according to claim 1 , wherein a surface oxide layer of the stainless steel has a bandgap energy of 2 eV or less.

3 . The stainless steel for a fuel cell separator according to claim 1 , wherein the surface oxide layer of the stainless steel forms an ohmic contact with the matrix.

4 . A method for manufacturing the stainless steel for a fuel cell separator having excellent surface hydrophilicity and electrical conductivity according to claim 1 , the method comprising a primary surface treatment of immersing a cold-rolled stainless steel sheet in a nonoxidizing acid solution and electrolyzing the stainless steel sheet after the immersing, and a secondary surface treatment of immersing the stainless steel sheet in an oxidizing acid solution.

5 . The method according to claim 4 , wherein the primary surface treatment comprises immersing the cold-rolled stainless steel sheet in the nonoxidizing acid solution for 5 seconds or more, or electrolyzing the stainless steel sheet at a current density of 0.1 A/cm 2 or more for 5 seconds or more after the immersing, wherein the nonoxidizing acid solution is a hydrochloric acid or sulfuric acid solution with a concentration of 5 wt % or more at 50° C. or higher.

6 . The method according to claim 4 , wherein the secondary surface treatment comprises immersing the cold-rolled stainless steel sheet in the oxidizing acid solution for 5 seconds or more, wherein the oxidizing acid solution is a nitric acid solution with a concentration of 5 wt % or more at 50° C. or higher.

Assignees

• Posco Co Ltd

Inventors

• Kim Jong-Hee
• Lim Kyuwan
• Seo Bo-Sung
• Kim Kwangmin
• Kim Young-Hwan

Classifications

• C23G1/081 Primary

  solutions containing H2SO4 · CPC title

• C23G1/085

  solutions containing HNO3 · CPC title

• C23G1/00

  Cleaning or pickling metallic material with solutions or molten salts (with organic solvents C23G5/02) · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C22C38/04

  containing manganese · CPC title