Reference electrodes
A reference electrode is a half cell with an electrode potential which is established quick, constant, reproducible and stable over time. When specifying potentials, you should always state the reference electrode against which you determined the potential.
If you want to measure conforming to standards you should use the platinum-hydrogen electrode. In doing so, the platinum-hydrogen electrode has to be connected to the negative pole (mass or com entrance). Mass entrances are assigned a potential of zero. It represents the reference potential for all signal and operating voltages.
With the platinum-hydrogen reference electrode, the hydrogen potential depends on the pH value of the measurement solution.
The hydrogen potential depends on the pH value of the measurement solution. Here, the potentials of the silver respectively the calomel electrode are plotted against the platinum-hydrogen electrode (RHE – reversible hydrogen electrode placed on mass). With a polarity reversal the algebraic signs are reversed accordingly.
HydroFlex – the platinum-hydrogen reference electrode
The platinum-hydrogen reference electrode is the first choice to measure potentials conforming to standards. Platinum-hydrogen electrodes are the only reference electrodes that directly measure hydrogen ion activity. When immersed in the measuring solution, it is a so-called an indicator electrode.
The hydrogen electrode is made of PTFE, the edging is made of PEEK. It is
120 mm long – as big as a pen – and thus very handy. The shaft has an outside diameter of 8 mm and a length of 80 mm. By activating the hydrogen generation cell (Cartridge) the hydrogen production is started and the interior of the PTFE-tube is charged with hydrogen until it leaks out of the platinum hydrogen electrode.
Hydrogen reference electrode HydroFlex
Composition of the reference electrode HydroFlex
The voltage is measured at the gold-plated socket in the electrode’s head. Multimeters for measuring voltage should have an input resistance of 5 MOhm and more. Our reference electrode is of low-impedance so that shielded cables are not needed. The HydroFlex can be used up to temperatures of 210°C as long as only the PTFE-shaft is exposed to those temperatures.
The benefits are quite obvious. The electrode provides itself with hydrogen gas by an internal supply which can easily be exchanged. It does not contain any interior electrolyte thus there is no ion-discharge and no diffusion potential. The HydroFlex is low-maintenance because no electrolyte has to be refilled. It does not contain any heavy metals.
The electrode can be used in concentrated fluoride electrolytes and in strongly acidic or strongly alkaline mediums (pH -2 to 16) because it is made out of PTFE.
Before the first use, the hydrogen electrode HydroFlex must be activated so that hydrogen production can start in the hydrogen generation cell. The arising hydrogen fills the PTFE-tube and leaks out of the platinum-palladium electrode, where – corresponding to the ions in the solution – a hydrogen potential sets. The hydrogen potential can be gripped at the gold-plated socket in the electrode head. Once activated, the electrode works continuously for 6 months.
Principle of the reference electrode HydroFlex – a hydrogen electrode
Step-by-step manual for the commissioning of the hydrogen electrode
The hydrogen supply has to be activated before the first use. For the functioning of the electrode it is important to stick to the following instructions:
Step-by-step manual for the activation of the hydrogen electrode HydroFlex
Please do not remove the labelling with the serial number and the sticker with the activation date.
download - Step-by-step manual for the activation of the hydrogen electrode HydroFlexActivation of hydrogen electrode HydroFlex
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Storage of the hydrogen electrode HydroFlex
After measuring, rinse the hydrogen electrode thoroughly with water. Please always place the electrodes in a liquid – e.g. measure solution, 1 mol/l hydrochloric acid, 1 mol/l caustic soda – even when you are not measuring. The hydrogen electrodes must not be stored dry in air! We recommend not changing the runtime of the HydroFlex.
Checking the functioning of the HydroFlexReplacement of the cartridge of the HydroFlex
The functioning of the hydrogen electrode is ensured as long as hydrogen is generated (runtime). After 6 months (set and suggested duration) the hydrogen supply has to be replaced. Exceeding the runtime can lead to defects in the hydrogen electrode and should be avoided at all costs. If it is not possible to change the hydrogen cartridge, the hydrogen electrode must be removed from the liquid and stored dry until a new hydrogen cartridge can be inserted.
You can remove the old hydrogen supply with a SW21-ring-spanner and replace it with a new one. Mind the correct hub of the O-ring when you install the new hydrogen supply. The O-ring must not push itself out. Seal the screw thread with a universal grease (e.g. Korasilon-paste highly viscous). The spent Cartridge has to be disposed of as battery garbage.
You can replace the cartridge of hydrogen electrode HydroFlex very easily
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Complete cleaning of the HydroFlex
Sometimes a complete cleaning of the HydroFlex is required – especially when there are visible deposits on the electrode.
download manual - Complete cleaning of the hydrogen electrode HydroFlex
Complete cleaning of the hydrogen electrode HydroFlex
The potential is not displayed correctly.
Cause 1: bad contacting
Check the measuring cables on optical damages such as corrosion, cracks and sessile plugs. Replace the cable. Check the electrode with an external reference electrode, e.g. a calomel or silver silver chloride electrode.
Cause 3: slow ion exchange, e.g. when you switch from concentrated solutions to weak concentrated solutions
Await the setting time, sometimes the balancing of concentrations takes longer than expected. If necessary, check the potential in another electrolyte such as 1 mol/l hydrochloric acid.
Cause 2: no or too low hydrogen production
Was the hydrogen electrode activated properly?
If not, please activate the hydrogen electrode.
Did you await the activation phase of 24h?
If not, wait 24h before you measure.
Has the runtime of the cartridge been exceeded?
If yes, please clean the hydrogen electrode as described above and replace the old cartridge with a new one. The new cartridge also must be activated before you can use it.
Cause 4: air/oxygen gets to the electrode
Avoid that gases such as air or oxygen reach the hydrogen electrode’s shaft. If this happens the hydrogen is displaced or reacts off. No hydrogen potential can be established.
Fluctuating, noisy or oscillating potentials.
Cause 1: hydrogen bubbles of the hydrogen electrode itself
Bubbles are continuously leaking out of the hydrogen electrode. Some bubbles are small, others are bigger. Usually, they do not disturb your measurements.
Is a big bubble forming at the bottom of the hydrogen electrode which sticks to the vessel wall? If possible, place the electrode further away from the vessel wall or hang the hydrogen electrode transversely into the measuring vessel.
Cause 2: induced gases
Change the position of your gas inlet. Induced gas bubbles which are piped by close to the hydrogen electrode can disturb the measurements and lead to fluctuating potentials.
Cause 3: potentiostat or measuring device
Check your measuring device.
If you measure in low conductive electrolytes, potentiostats and measuring devices quickly reach their limits.
More information about noise in electrochemical measurements can be found here: What-can-cause-my-experiment-to-be-noisy
Deposits (e.g. red or brown) on the electrode.
The hydrogen electrode is contaminated and a mixed potential is set
Check the runtime of the hydrogen supply. If necessary, the hydrogen cartridge must be replaced.
Wipe the electrode with a cloth or clean it in 1 mol/l nitric acid and rinse it with distilled water.
If necessary, you can carry out a complete cleaning.
If that is no successful, the electrode is so badly contaminated that we suggest a new purchase.
Mini hydrogen electrode – Mini-HydroFlex
We have further developed and reduced the size of our hydrogen electrode for use in confined spaces. The structure and functionality correspond to our hydrogen electrode HydroFlex – just smaller.
The Mini-HydroFlex can be used for temperatures up to 80°C and works without inner electrolyte. Currently, we offer the Mini-HydroFlex as a PEEK-capillary. The capillary has a diameter of 1.6 mm and enables the use of Mini-HydroFlex in small openings.
The capillary’s standard length is 53,5 mm, other lengths are available at an additional charge. Thus the Mini-HydroFlex can be individually designed according to your needs.
download manual mini-HydroFlex
Mini hydrogen reference electrode Mini-HydroFlex
Composition of the mini hydrogen electrode Mini-HydroFlex
Before you measure, you must insert the supplied hydrogen cell (button cell) into the electrode head and place the mini hydrogen electrode in water for 24 hours preferably.
Please do not remove the labelling with the serial number and the sticker with the activation date.
Step-by-step manual for the commissioning of the mini hydrogen electrode mini HydroFlex
Step-by-step manual for the commissioning of the mini hydrogen electrode mini HydroFlex
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Storage of the mini hydrogen electrode Mini-HydroFlex
After your measurements rinse the electrode thorough with water. Even when you are not measuring, please always place the mini hydrogen electrode in a liquid, e.g. measuring solution, 1 mol/l hydrochloric acid or 1 mol/l caustic soda. Hydrogen electrodes must not be stored dry in air!
Replacement of the hydrogen cell
In a few steps, the hydrogen cell of the Mini HydroFlex electrode can be replaced
After reaching the runtime of 12 months the hydrogen button cell has to be replaced. The exceedance of the duration can lead to defects of the hydrogen electrode and should be avoided absolutely. If the replacement of the hydrogen cell not possible the hydrogen electrode has to be taken out of the liquid and be stored dry until a new hydrogen cell can be inserted.
download - Replace of the hydrogen cell in Mini-HydroFlex
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The potential is not displayed correctly.
Cause 1: bad contacting
Check the measuring cables on optical damages such as corrosion, cracks and sessile plugs. Replace the cable. Check the electrode with an external reference electrode, e.g. a calomel or silver silver chloride electrode.
Cause 3: slow ion exchange, e.g. when you switch from concentrated solutions to weak concentrated solutions
Await the setting time, sometimes the balancing of concentrations takes longer than expected. If necessary, check the potential in another electrolyte such as 1 mol/l hydrochloric acid.
Cause 2: no or too low hydrogen production
Did you place the new Mini-HydroFlex in the measuring solution for 24 hours?
If not, wait 24 hours before you measure.
Has the runtime of the hydrogen source been exceeded?
If yes, please replace the hydrogen cell.
Cause 4: air/oxygen gets to the electrode
Avoid that gases such as air or oxygen reach the hydrogen electrode’s shaft. If this happens the hydrogen is displaced or reacts off. No hydrogen potential can be set.
Fluctuating, noisy or oscillating potentials.
Cause 1: hydrogen bubbles of the hydrogen electrode itself
Bubbles are continuously leaking out of the hydrogen electrode. Some bubbles are small, others are bigger. Usually, they do not disturb your measurements.
Is a big bubble forming at the bottom of the hydrogen electrode which sticks to the vessel wall? If possible, place the electrode further away from the vessel wall or hang the hydrogen electrode transversely into the measuring vessel.
Cause 2: induced gases
Change the position of your gas inlet. Induced gas bubbles which are piped by close to the hydrogen electrode can disturb the measurements and lead to fluctuating potentials.
Cause 3: potentiostat or measuring device
Check your measuring device.
If you measure in low conductive electrolytes potentiostats and measuring devices quickly reach their limits.
More information about noise in electrochemical measurements can be found here: What-can-cause-my-experiment-to-be-noisy
Deposits (e.g. red or brown) on the electrode.
The hydrogen electrode is contaminated and a mixed potential is set
Check the runtime of the hydrogen source. If necessary, the hydrogen cell must be replaced.
Some deposits can be wiped off with a cloth.
With 1000 grit sandpaper, you can carefully sand the bottom of the electrode.
More stubborn impurities dissolve in 1 mol/l nitric acid. The electrode must then be rinsed thoroughly in distilled water.
If the cleaning steps are unsuccessful, the electrode is unfortunately so contaminated that we recommend buying a new one.
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