Evaluation of the Measurement
The figure on the right shows the measured current in µA cm-2 of unalloyed steel with a thickness of 0.1 mm in 1 mol/L sodium hydroxide solution at room temperature.
First, the sample stands in 1 mol/L sodium hydroxide solution until only a small passivation current is measured. Then the actual measurement is started with a charging current of 10 mA/cm².
In the figure it can be seen, based on the negative hydrogen potential, that hydrogen is developed immediately at the starting point of the measurement. However, this is only detected after approx. 110 seconds on the other side of the sample. The hydrogen must first diffuse through the sample.
The permeation current increases with increasing measurement time. After 900 seconds, the charging current was set to 0 mA/cm² again. The permeation current slowly subsides as the hydrogen stored in the sheet diffuses out in a decay curve.
The passivation current at the beginning of the measurement decreases to a small constant offset. For an exact calculation of the permeation current, you have to correct the measured current by this offset. The figure on the right shows the corrected permeation current.
From the current height, Faraday’s law can be used to calculate the hydrogen volume diffused through the sample.
Faraday's law: Q = I * t = n * z * F
Molare Volume: Vm = V/n = 22,4 L/mol
Volume: V = I * t * Vm / (z * F) in L / (cm2 s)
Faraday constant F = 96485 A s / mol
Charge Q in A s
Current I in A
Time t in Seconds
Nummer of transferred electrons n = 2 (for hydrogen reaction)
Would you like to learn more about hydrogen permeation?
Basics about Hydrogen Permeation
Here you will find an overview of typically used terms and some useful basics for hydrogen permeation measurements.
How to Measure Hydrogen Permeation
Our concept is characterised by less technical equipment. The measuring cell consists of a reduction cell (charging cell) and an oxidation cell (fuel cell). The test piece is located between these two subcells. To detect the permeation current, an oxygen consumption electrode (oxygen gas diffusion electrode O2-GDE) is used on the oxidation side of the test piece.