Method for producing stainless steel plate for fuel cell separator

[0169] ·Example 1

[0170] Prepare a stainless steel plate (bright annealing plate) with a thickness of 0.10 mm with the composition described in Table 1 (the remainder is Fe and unavoidable impurities), and perform cathodic electrolysis on the stainless steel plate under the conditions shown in Table 2. Treatment to remove the oxide film formed on the surface of the steel sheet. Next, under the conditions shown in Table 2, electrolytic etching was performed by potential control, and then, under the conditions shown in Table 2, immersion treatment was performed as a surface stabilization treatment to obtain a stainless steel plate for a separator. It should be noted that the potentials in Table 2 are relative to the potential of the reference electrode (Vvs.Ag/AgCl).

[0171] Here, when electrolytic etching is performed by potential control, Ag/AgCl is used as a reference electrode in advance, in a 30g/L sulfuric acid aqueous solution, 55°C, and a potential scanning speed of 1mV/s for each steel Kindly obtain the anode polarization curve. Regarding steel grade A, it is confirmed that the potential range of -0.51~-0.34V (vs.Ag/AgCl) is the active zone, which is greater than the potential of -0.34~+0.97V (vs.Ag/AgCl) The range is the passivation zone, and the potential range greater than +0.97V (vs.Ag/AgCl) is the overpassivation zone. Regarding steel grade B, it is confirmed that the potential range of -0.49~-0.39V (vs.Ag/AgCl) is the active zone, and the potential range greater than -0.39~+1.00V (vs.Ag/AgCl) is the passivation zone, which is greater than The potential range of +1.00V (vs.Ag/AgCl) is the overpassivation zone.

[0172] In addition, regarding steel grade C, it was confirmed that the potential range of -0.25~-0.19V (vs.Ag/AgCl) was the active zone, and the potential range greater than -0.19~+0.92V (vs.Ag/AgCl) was the passivation zone. , The potential range greater than +0.92V (vs.Ag/AgCl) is the overpassivation zone.

[0173] In addition, regarding steel grade D, it was confirmed that the potential range from -0.34 to -0.19V (vs.Ag/AgCl) is the active zone, and the potential range from -0.19 to +0.98V (vs.Ag/AgCl) is the passivation zone. , The potential range greater than +0.98V (vs.Ag/AgCl) is the overpassivation zone.

[0174] In addition, regarding steel grade E, it was confirmed that the potential range of -0.35~-0.20V (vs.Ag/AgCl) was the active zone, and the potential range greater than -0.20~+0.96V (vs.Ag/AgCl) was blunt. In the chemical zone, the potential range greater than +0.96V (vs.Ag/AgCl) is the overpassivation zone.

[0175] In addition, the immersion treatment after the electrolytic etching treatment was performed by immersing in a 300 g/L nitric acid aqueous solution for 5 minutes or 15 minutes under the condition of a treatment temperature of 55°C.

[0176] Using the stainless steel plate for separators thus obtained, the contact resistance was evaluated according to the following points.

[0177] The contact resistance is calculated as follows: A predetermined sample is clamped with carbon paper (TGP-H-120, Toray Co., Ltd.), and then the electrode coated with gold on the copper plate is contacted from both sides, and 0.98MPa per unit area (=10kg) /cm 2 ) Pressure and current flow, measure the voltage difference between the electrodes, calculate the resistance. Then, the value obtained by multiplying the measured value of the electrical resistance by the area of ​​the contact surface was taken as the contact resistance value.

[0178] In addition, it is assumed that some kind of heat treatment of these stainless steel plates for separators is carried out in the fuel cell stack manufacturing process. The heat treatment is carried out at 200°C for 2 hours in an air atmosphere, and the following criteria are passed according to the same points as above. The contact resistance value of the stainless steel plate after the heat treatment was calculated. Table 2 shows these evaluation results.

[0179] Here, the contact resistance value before heat treatment is 20.0mΩ·cm 2 In the following cases, it is determined that low contact resistance is obtained.

[0180] In addition, the contact resistance value after heat treatment is 30.0mΩ·cm 2 In the following cases, it is determined that the low contact resistance is maintained after the heat treatment.

[0181] It should be noted that the evaluation of the contact resistance after the heat treatment was omitted for the samples for which low contact resistance was not obtained before the heat treatment.

[0182]

[0183] According to Table 2, the following matters are obvious.

[0184] (a) For the invention examples, the desired low contact resistance was obtained. In particular, the invention example in which the stabilization treatment was performed after the electrolytic etching treatment maintained low contact resistance even after the heat treatment. In addition, these steel sheets can be manufactured without using hydrofluoric acid, and therefore are extremely advantageous in terms of safety and mass productivity.

[0185] (b) On the other hand, in the comparative examples, none of the comparative examples obtained the desired contact resistance in the stage before the heat treatment.

[0186] ·Example 2

[0187] Prepare a stainless steel plate (bright annealed plate) with a thickness of 0.10 mm with the composition described in Table 1 (the remainder is Fe and unavoidable impurities), and the stainless steel plate is made under the conditions shown in Table 3 and Table 4. Cathodic electrolysis is performed to remove the oxide film formed on the surface of the steel sheet. Next, under the conditions shown in Table 3 and Table 4, electrolytic etching treatment was performed by current control, and then, under the conditions shown in Table 3 and Table 4, immersion treatment or electrolytic treatment was performed as a surface stabilization treatment to obtain Stainless steel plate for separator (It should be noted that the current density in Tables 3 and 4 is the value obtained by dividing the current flowing between the stainless steel plate used as the material to be processed and the counter electrode by the surface area of ​​the material to be processed) . However, for sample No. 18, the cathodic electrolysis treatment as a removal treatment of the oxide film was not performed, and for samples Nos. 19, 28, and 35, the immersion treatment and electrolysis treatment as the surface stabilization treatment were not performed.

[0188] Here, when electrolytic etching is performed by current control, in advance, in a 30g/L sulfuric acid aqueous solution at 55°C, the current density and the current density applied to the stainless steel plate as the material to be processed and the pair of The relationship of the electrolysis voltage between the electrodes is confirmed from the range where the electrolysis voltage increases sharply: For steel grade A, if the current density is adjusted to +0.5~+7.5mA/cm 2 The range is the activation zone. For steel type B, if the current density is adjusted to +0.03~+0.3mA/cm 2 The range is the activation zone. For steel grade C, if the current density is adjusted to +0.03~+0.3mA/cm 2 The range is the activation zone. For steel grades D and E, if the current density is adjusted to +0.03mA/cm 2 , It is the activation zone.

[0189] In addition, it is confirmed that for steel grade A, if the current density is +15.0mA/cm 2 Above, it is the overpassivation zone. For steel type B, if the current density is +7.5mA/cm 2 Above, it is the overpassivation zone. For steel grade C, if the current density is +15.0A/cm 2 Above, it is the overpassivation zone. For steel grade D, if the current density is +15.0mA/cm 2 Above, it is the overpassivation zone. For steel grade E, if the current density is +15.0mA/cm 2 Above, it is the overpassivation zone.

[0190] Similarly, regarding steel grade A, it was confirmed that:

[0191] In 30g/L hydrochloric acid aqueous solution and under the condition of 55℃, if the current density is adjusted to +0.8mA/cm 2 ,

[0192] In addition, in a mixed aqueous solution of 15g/L sulfuric acid + 15g/L hydrochloric acid at 55°C, in a 30g/L sulfuric acid + 0.5g/L hydrofluoric acid aqueous solution at 55°C, and at 30g/L sulfuric acid +1g/L nitric acid aqueous solution and under the condition of 55℃, if the current density is adjusted to +1.0mA/cm 2 ,

[0193] They are all activated areas.

[0194] In addition, regarding steel type B, it was confirmed that: in 30 g/L sulfuric acid aqueous solution and 65°C, 30 g/L sulfuric acid aqueous solution and 70°C, and 30 g/L hydrochloric acid aqueous solution and 70°C If the current density is adjusted to +0.03mA/cm 2 , Are all activated areas.

[0195] In addition, regarding steel grade D, it was confirmed that if the current density is adjusted to +0.03mA/ in a 30g/L sulfuric acid aqueous solution and 70°C and in a 30g/L sulfuric acid aqueous solution and 75°C. cm 2 , Are all activated areas.

[0196] It should be noted that the immersion treatment after the electrolytic etching treatment is performed by immersion in a 300 g/L nitric acid aqueous solution at a treatment temperature of 55° C. for 0.5 minutes, 1 minute, 5 minutes, 15 minutes, or 30 minutes.

[0197] In addition, the electrolytic treatment after the electrolytic etching treatment was performed using a 50 g/L nitric acid aqueous solution under the conditions of a treatment temperature of 55° C., a potential of +0.50 V (vs. Ag/AgCl), and a treatment time of 5 minutes. It should be noted that for the stainless steel plate of Steel No. A, the potential of +0.50V (vs.Ag/AgCl) is the passivation zone.

[0198] Using the stainless steel plate for separators thus obtained, the contact resistance was evaluated in accordance with the same points as in Example 1. The evaluation results are shown in Tables 3 and 4.

[0199]

[0200]

[0201] According to Tables 3 and 4, the following matters are obvious.

[0202] (a) For the invention examples, the desired low contact resistance was obtained. In particular, the invention example subjected to appropriate stabilization treatment maintained low contact resistance even after the heat treatment. In addition, these steel sheets can be manufactured without using hydrofluoric acid, and therefore are extremely advantageous in terms of safety and mass productivity.

[0203] (b) On the other hand, in the comparative examples, none of the comparative examples obtained the desired contact resistance in the stage before the heat treatment.