Hydrogen permeation test by a bipotentiostat

Hydrogen permeation test in steel

Experimental purpose

This experiment aims to measuring the atomic hydrogen content in steel and the diffusion rate of them.

Experiment Setup

Fig. 1 Hydrogen permeation test setup

Solution preparation:

Nickel-plating solution (commercial nickel plating solution)

Anode chamber: 0.2mol/L KOH

Cathode chamber: 0.1mol/L HCl

Instrument &electrodes:

Bipotentiostat model CS2350M

Nickel-plating cell (coating evaluation cell)*1 pcs

H-cells* 1 set

Hg/HgO reference electrode 1 pcs

Q235 carbon steel plate (5cm*5cm*0.5 mm) 1 pcs

Platinum counter electrode *2 pcs

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Experiment steps

(1) Specimen pre-processing

Before the experiment, the carbon steel specimen was polished to a mirror surface with 180#, 400#, 600#, 1000#, and 2000# sandpaper in order, then it was washed with water, wiped with ethanol, and dried in cold air. The specimen was immersed in 0.1 mol/L HCl for 3 min, rinsed with water, and then it was immersed in 0.2 mol/L KOH for 3 min, rinsed with water, dried and placed in a desiccator for use.

(2) Nickel-plating

Fig 2 Electrolytic cell and electrode connection for Nickel plating

As is shown in Figure 2, we used the coating evaluation cell(CS934) to do the nickel-plating. Clamp the carbon steel sheet, add the nickel- plating solution into the cell, then put a small piece of nickel foam into the solution. The red (CE) & yellow alligator (RE) jointly clamp the nickel foam strip, and the green alligator (WE) clampS to the carbon steel(If there is a white sense lead, you should connect together with green WE). Then conduct the “Galvanostatic” test.

Fig. 3 Parameter setting of Nickel plating

Set the applied current to be -10 mA/cm2. The exposure area of the specimen was about 7.065cm², so we applied -70.65 mA. You can set the electrode area in “cell setting”).

Fig. 4 electrode area modification interface

The plating process lasted for 30 minutes. After it’s completed, please wash the metal with distilled water, dry in cold air, and then place it in a desiccator for use.

(2) Hydrogen permeation test

Fig. 5. Bipotentiostat CS2350M and H-cells

In anode chamber (left cell), it is a 3-electrode system:

- Working electrode: nickel-plated surface of the carbon steel

- Reference electrode: Hg/HgO electrode

- Counter electrode: platinum electrode

The hydrogen charging side(right cell) adopts a two-electrode system.

- Anode: the non-nickel-plated surface of carbon steel,connecting to WE alligator

- Cathode: the platinum electrode, connecting to yellow (RE) & red(CE) alligators together.

Firstly, add 250 mL 0.2 mol/L KOH solution to the anode chamber(left), and 250ml 0.1 mol/L HCl to the cathode chamber(right cell), turn on the bipotentiostat, select “Bipotentiostat”→Hydrogen Diffusion Test.

Fig. 6. Parameters setting for hydrogen diffusion test

Set the parameters as figure 6: the polarization potential is 0.45 V, the hydrogen charging peak current is -22.6 mA (10 mA/cm2), and the hydrogen charging valley current is 0.

As the atomic hydrogen [H] in the carbon steel gradually diffuses to the surface and is oxidized into H+, the anodic residual current will gradually be stable.

When the residual current is less than 1 mA/ cm², in the right cell (hydrogen charging)the following reaction will occur:

Result and analysis

Hydrogen diffusion coefficient

Fig. 7. Oxidation current -time curve in hydrogen diffusion test

From fig. 7 we can obtain I_max=1.0058×10^-5 A·cm^-2. Find the time t when I_t / I_max= 0. 63，

t = 2.380 h = 8568 s.

The time to start hydrogen charging is 5472 s，so lag time t_L=3096 s，thickness of the carbon steel L=0.1cm, according to the formula:

We can calculate the diffusion coefficient D=5.383×10^-7cm²/ s.