gaskatel Test Cell ElyFlow Bedienungsanleitung Seite 38

Reference electrode
Gaskatel test cells are optimized for the use of the reversible hydrogen reference
electrodes (RHE) Mini-HydroFlex.
In contrast to the usually used calomel or silver electrodes, these hydrogen reference
electrodes do not introduce any foreign electrolyte into the measuring solution. This is
very important for corrosion measurements, for example, where the smallest amounts of
chloride can drastically influence and falsify the results.
Most electrochemical reactions are pH dependent. This is compensated using Mini-
HydroFlex, because Mini-HydroFlex itself is also pH-dependent.
Position of the reference electrode – Haber-Luggin-capillary
For precise potential measurements it is necessary that the reference electrode is
positioned close to the working electrode.
To reduce the voltage drop across the electrolyte, the so-called IR drop, Haber-Luggin
capillaries are used. However, for measurement results to be comparable between cells,
the Haber-Luggin capillary must meet very precise and reproducible requirements.
The field lines in the electrolyte must not be disturbed (small diameter of the Haber-
Luggin-capillary). In turn, a large diameter of the Haber-Luggin-capillary is necessary for
low electrolyte resistance. Therefore, the Haber-Luggin-capillaries in Gaskatel test cells
are located outside the electrolyte space. This allows a slightly larger diameter without
disturbing the field lines.
The capillary must end at a defined, fixed distance from the working electrode. From a
quality assurance point of view, it is also important that all these factors are kept
constant for different half-cells.
This is where the precision of CNC manufacturing in plastic helps. The Gaskatel
measuring cells have very precise Haber-Luggin capillaries that end at the working
electrode. This makes the measurements very precise and comparable.
The capillaries must not be blocked by gas bubbles, as this leads to contact losses
during the potential measurement. The resistance then increases dramatically and the
potentiostat starts to oscillate.
Therefore, the Haber-Luggin capillaries in the FlexCell measuring cells are filled with a
solid electrolyte.
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