How to Measure Hydrogen Permeation
Easy Measurement of 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. This one must not be supplied with air, as the resulting currents are very low.
In practice, your test piece to be analysed is installed as a working electrode between two ElyFlow analysis chambers. The oxygen consumption electrode is installed in the working electrode holder of ElyFlow.
The electrolyte and electrode potential on the oxidation side must be selected so that the metal there is passivated but corrosion-resistant. Usually, caustic soda is used.
The hydrogen on the reduction side (hydrogen evolution side) can be generated chemically by pickling in a corrosive medium or in a special test medium. The surface of the test piece is charged with hydrogen (charging cell). The hydrogen atoms must be generated on the entire test surface. This method is therefore not suitable for systems that are prone to pitting corrosion.
In practice, you need the counter electrode with installed counter electrode. Otherwise the heating elements will be destroyed by the etch.
The counter electrode holder of the ElyFlow measuring cell contains a nickel electrode. However, this can be replaced with another counter electrode if nickel is not resistant in your electrolyte.
Alternatively, the hydrogen on the reduction side (hydrogen evolution side) can be generated electrochemically in a non-corrosive medium by a low current (charging current) on the test piece (metal membrane). The surface of the test piece is charged with hydrogen (charging cell). The hydrogen atoms must be generated on the entire test surface. This method is therefore not suitable for systems that are prone to pitting corrosion.
As soon as hydrogen is produced on the test piece and diffuses through it, the test piece becomes a hydrogen electrode on the side facing the oxygen electrode. There the hydrogen is oxidised. This results in a fuel cell that is discharged (fuel cell side BZS).
The oxidation current (fuel cell current) flowing between the test piece and the oxygen electrode must be measured. The more hydrogen diffuses through the sample, the higher the current.
In order to be able to evaluate the change in the surface, the potential of the test piece on the oxidation side can be measured during the entire measurement. The potential should remain approximately constant during the measurement. Significant changes in the potential indicate a change in the surface state and discontinuous interface conditions.
If you want to measure the potential, you have to use a Mini-HydroFlex in the reservoir with the Haber-Luggin capillaries directed to the test piece!
In case of electrochemical hydrogen generation, you can use a separator to protect your sample from byproducts and impurities of the counter electrode.
In this case, you will need an additional ElyFlow analyte compartment and a separator.
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.
Evaluation of the Measurement
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 Importance of Haber-Luggin Capillaries
The electrolytical contact between the working and the reference electrode is made by the Haber-Luggin capillary. It has to be positioned directly in front of the working electrode to minimize the voltage drop (IR-drop) across the electrolyte.