Frequently Asked Questions and Problems
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The Mini-HydroFlex reference electrode is designed for our test cells FlexCell and ElyFlow. However, it offers additional advantages such as adjustable length and a relatively small diameter.
However, please keep in mind that you will need an additional test lead.
The HydroFlex, on the other hand, is more robust and, with a diameter of 8 mm, follows the recommendations for the outer dimensions of reference electrodes.
Please note that our HydroFlex is not compatible with the test cell ElyFlow! You have to use the Mini-HydroFlex instead.
You can use our HydroFlex in FlexCell, though. You will then need an additional connector available for FlexCell-PP or FlexCell-PTFE as well as an additional test lead.
Yes. Because of the exact position of the reference electrode and the usage of a Haber-Luggin capillary, you always measure the correct potential. The large distance between the working electrode and counter electrode ensures that the entire working electrode has the same potential, regardless of the position on the surface.
Usually, you should place the reference electrode in front of the working electrode. However, you can also measure the voltage drop across the membrane or measure the potential at four different positions simultaneously.
ElyFlow is the most flexible electrochemical test cell. Of course, we have implemented the same ideas regarding an internal Haber-Luggin capillary within the cell and an internal heating device as in FlexCell.
The main difference is that you can direct an electrolyte flow through the cell ElyFlow. You can also combine multiple compartments to build up a cell with a single flow or two flows for anolyte and catholyte. Even a set up with three or more compartments is manageable.
Without applying an electrical current through the cell – that is, measuring open circuit potentials – tests can be done in any kind of cell.
However, when applying an electrical current to your cell, this will create an ohmic drop in the electrolyte. In order to handle this ohmic drop you, have to ensure the following:
- The counter electrode is the same size as the working electrode, and the activity of the counter electrode should always be high enough to support the reaction at the working electrode.
- The field line distribution within the cell must be parallel – otherwise, the current density of the working electrode is not homogeneous.
- You need a Haber-Luggin capillary to measure the exact potential without IR Drop correction.
FlexCell is optimized for these requests.
If your electrochemical reaction yields to products which change the electrolyte, you must set up an electrolyte flow and pump the products out of the cell. These can be gases or liquid products, such as in CO2 reduction, for example. In this case you need to use ElyFlow.
If the reaction involves more than just water splitting, the anode and cathode should be separated. This is achieved by using two electrolyte compartments from ElyFlow – separated by a membrane or separator. The standard separator is a Nafion membrane N424.
FlexCell can be used for all reactions without huge amounts of gas evolution at the working electrode. This includes corrosion tests on metal plates or gas-consuming reactions such as hydrogen oxidation, oxygen reduction, carbon dioxide reduction, etc. When producing gases, these reaction products can stick to the working electrode or in the electrolyte compartment and block further reactions.
The cell can be filled with approx. 30 ml of electrolyte through the opening in the cover. Pour in the last ml slowly and observe the filling level in the hole for the reference electrode, which may rise with a delay. The hole should be no more than half full to avoid overflow when setting the reference electrode.
If the hole does not fill with electrolyte, an air bubble in the Haber-Luggin capillary is blocking the electrolyte flow. Tilt the measuring cell slightly to allpw the air bubbles to escape.
Avoid an electrolyte film between reference electrode and working electrode because a film can lead to a short circuit.
The cell can be filled with approx. 25 ml of electrolyte through the center opening of the analyte compartment. Pour in the last ml slowly and observe the filling level in both reservpoirs for the reference electrodes, which may rise with a delay. If the hole does not fill with electrolyte, an air bubble in the Haber-Luggin capillary is blocking the electrolyte flow. Tilt the measuring cell slightly to allow the air bubbles to escape.
This could be due to poor contact. Please check the connection cables of the heating elements.
Alternatively, the silicone-coated PTC heating element may be defective. Check the resistance of the heating elements when cold:
FlexCell PTFE: 5 Ohm
FlexCell PP: 3 Ohm
ElyFlow: 15 Ohm
The counter electrode is in direct contact to a 24 V heating element. This heats the electrolyte near the counter electrode.
If you have a divided cell with a membrane or separator separating the counter electrolyte and the working electrolyte, an external heated beaker should be used to also adjust the temperature of the working electrolyte.
The choice of the sealings is depending on the kind of sample and electrolyte.
For measurements of gas diffusion electrodes, use flat silicone sealings.
For measurements in very strong alkalis and acids at high temperatures, we offer sealings made of PTFE.
For poorly conductive electrodes, we offer sealings made of graphite.
O-rings are recommended for metal sheets. Suitable for alkaline solutions are O-rings made of EPDM.
For use in acids, we recommend O-rings made of FKM.
Due to the limited electrolyte volume of approximately 30 ml, the test duration is limited to 24h or several days, depending on the current density and the temperature (water evaporation losses).
This is determined by the current density and the external volume of your electrolyte storage. Several days to weeks are possible.
Yes, you can purge the cell with Argon, for example. Make sure that the purge rate is low to avoid removing too much water vapour.
No. Due to the large distance of approxiametly 60 mm between the counter and working electrodes, a high voltage loss occurs due to the limited conductivity of the electrolyte.
This could be due to poor contacts. Check the connecting leads of the potentiostat, and the multilam plugs of the cell.
For FlexCell: Alternatively, the Pt counter electrode could be the problem. Remove the counter electrode and check its condition.
There may be gas bubbles in front of the reference electrode. Move the reference electrode up and down a few centimeters.
The gas bubbles may also be blocking the Haber-Luggin capillary. In this case, remove the air from the reference electrode hole using a pipette ball.
Contaminations, degradation products, corrosion products can lead to incorrect measurements, too.
Please check the measuring cables if there are any visual damages such as corrosion, cracks or sessile plugs. Replace the cables.
An infirm battery of handheld multimeter can also lead to wrong voltages.
The potentiostat often reacts very delicate to electrolytes and/or samples with inadequate conductivity or gas bubbles in the Haber-Luggin capillary. It begins to oscillate.
The impedance of the reference electrode or Haber-Luggin capillary may be too high. Please adjust the current range of the potentiostat.
If using an analyte compartment, please insert the reference electrode into it.
You can find more helpful information here: What-can-cause-my-experiment-to-be-noisy.
The screw connections may not be sealed. Please tighten them.
Also, check that the O-ring or silicone sealing is properly seated. You can also check the contact screws and the fixing pins for this.
It is usually sufficient to rinse the cell thoroughly with water after disassembly.
Deposits can be removed mechanically using a suitable laboratory brush.
Stubborn metal deposits such as silver or copper can be removed with nitric acid.
You can remove the counter electrode for cleaning or replacing it. Take a look at our video.
The nickel counter electrode is only suitable for use in alkaline media in the pH range of pH 10 to pH 16.
In the pH range of pH -2 to pH 10, you have to use the MMO counter electrode.
The Mini-HydroFlex reference electrode is designed for our test cells FlexCell and ElyFlow. However, it offers additional advantages such as adjustable length and a relatively small diameter.
However, please keep in mind that you will need an additional test lead.
The HydroFlex, on the other hand, is more robust and, with a diameter of 8 mm, follows the recommendations for the outer dimensions of reference electrodes.
Please note that our HydroFlex is not compatible with the test cell ElyFlow! You have to use the Mini-HydroFlex instead.
You can use our HydroFlex in FlexCell, though. You will then need an additional connector available for FlexCell-PP or FlexCell-PTFE as well as an additional test lead.
Before the first use, the hydrogen electrode HydroFlex must be activated so that hydrogen production can start in the hydrogen generation cell. To do this, carefully remove the protective cap from the electrode. Turn the runtime on the head of the electrode clockwise to position 1 using a 3 mm hex screw driver.
Place HydroFlex in distilled water for 24 hours. At least half of the shaft should be surrounded by water. After 24 hours, adjust the runtime to 6 months. For correct use, this must not be changed.
Important: Please mark the activation month and year on the enclosed sticker and attach it to the HydroFlex.
Please do not remove the labelling with the serial number and the sticker with the activation date.
Commissioning of hydrogen electrode HydroFlex (youtube)
Before you start measuring, you must insert the supplied hydrogen cell (button cell) into the electrode head and place the mini hydrogen electrode in water for preferably 24 hours. Please do not remove the labelling with the serial number and the sticker with the activation date.
Commissioning of mini hydrogen electrode Mini-HydroFlex (youtube)
Commissioning of mini hydrogen electrode Mini-HydroFlex (pdf)
Yes, (Mini-)HydroFlex is an electrode of the first kind. You can place (Min-)HydroFlex directly into any kind of electrolyte.
Yes and no.
Measuring open-circuit potentials does not require a fixed position within the cell.
However, when applying some current to the electrochemical cell and thereby creating field line curvatures, you must use a Haber-Luggin capillary to adjust the correct position. Another advantage of the Haber-Luggin capillary is that it helps to protect the hydrogen electrode from parasitic oxygen gas bubbles.
After the measurements, rinse the electrode thoroughly with water. Place the hydrogen electrode in a liquid (such as measuring solution, 1 mol/l hydrochloric acid, 1 mol/l sodium hydroxide solution, water) to keep it functional. The hydrogen electrode should not be stored dry in air as long as the hydrogen cartridge is generating hydrogen - even when you are not measuring. Otherwise, a mixed potential forms which can lead to incorrect results.
Pay attention to the runtime of the hydrogen cartridge. As soon as the runtime of 6 months is reached, the hydrogen cartridge must be replaced immediately. Otherwise, a vacuum will form in the electrode and liquid can be soaked.
After your measurements, rinse the electrode thoroughly 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!
Nothing to do - (Mini-)HydroFlex is working without an internal buffer!
Yes, the replacement cells can be stored. However, please mind the best before date.
The expiration date depends on the date of manufacture.
As a general rule, you should activate the cells after about 18 months at the latest. If in doubt, just ask us.
The reference electrode itself has no expiration date. You just need to remember to use a new hydrogen cell.
There are no special storage instructions to follow.
Yes, this is very important.
The replacement cells for HydroFlex are not compatible with Mini-HydroFlex, and vice versa.
Please be sure to purchase the hydrogen cells for Mini-HydroFlex and the hydrogen cartridges for HydroFlex.
As soon as the running time of 6 months is reached, the hydrogen cartridge must be replaced immediately. Otherwise, a vacuum will form in the electrode and liquid can be soaked.
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.
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.
Replacment of hydrogen cartridge (youtube)
After reaching the runtime of 12 months, the hydrogen button cell has to be replaced. Exceeding the operating time can lead to defects of the hydrogen electrode and must be absolutely avoided.
If the replacement of the hydrogen cell is not possible, the hydrogen electrode has to be taken out of the liquid and stored dry until a new hydrogen cell can be inserted.
Replacment of hydrogen cell (youtube)
If you want to check (Mini-)HydroFlex, we recommend the standard calomel electrode or, if necessary, the silver silver chloride electrode. We recommend buffer pH 2.
Cause 1: Poor contacting
Check the test lead for visual damage such as corrosion, cracks, and stuck connectors. Replace the test leads.
Check the electrode using an external reference electrode, such as a calomel or silver chloride electrode.
Cause 2: No or insufficient hydrogen production
Have you placed the new, freshly activated (Mini-)HydroFlex in water for 24 hours?
If not, please wait 24 hours before starting the measurement!
Has the hydrogen cartridge/hydrogen cell reached the end of its service life?
If so, replace it.
Mini-HydroFlex: Replacment of hydrogen cell (youtube) / HydroFlex: Replacment of hydrogen cartridge (youtube)
Mini-HydroFlex: Replacement of hydrogen cell (pdf) / HydroFlex: Replacement of hydrogen cartridge (pdf)
Manual for Mini-HydroFlex (pdf) / HydroFlex: Manual for HydroFlex (pdf)
Cause 3: Slow ion exchange, e.g. when changing from concentrated solutions to weakly concentrated solutions
Please take the adjustment time into account – sometimes equilibration of concentrations simply takes much longer than expected.
If necessary, check the potential in a different electrolyte, such as 1 mol/L hydrochloric acid.
Cause 4: Air/oxygen reaches the hydrogen electrode
Avoid allowing gases such as air or oxygen to enter or contact the hydrogen electrode at the bottom of the shaft. This will displace the hydrogen or cause it to react. A hydrogen potential cannot be established.
Cause 1: Hydrogen bubbles from the hydrogen electrode itself
Gas bubbles continuously escape from the hydrogen electrode. These are sometimes very small, but sometimes larger. These usually do not interfere with your measurements.
Does a large bubble form at the bottom of the hydrogen electrode and cling to the vessel wall? If possible, position the hydrogen electrode further away from the vessel's edge, or hang it at an angle in the measuring vessel.
Cause 2: Induced gases
Change the position of your gas inlet.
Induced gas bubbles that pass close to the platinum-hydrogen electrode can interfere with the measurement and lead to fluctuating potentials.
Cause 3: Potentiostat or measuring device
Check your measuring device.
If you measure in poorly conductive electrolytes, the measuring devices and potentiostats quickly reach their limits.
More information about noise in electrochemical measurements can be found here: What-can-cause-my-experiment-to-be-noisy
The hydrogen electrode may be contaminated, resulting in a mixed potential.
Check the runtime of the hydrogen source. The hydrogen cartridge/cell may need to be replaced.
Mini-HydroFlex: Replacment of hydrogen cell (youtube) / HydroFlex: Replacment of hydrogen cartridge (youtube)
Mini-HydroFlex: Replacement of hydrogen cell (pdf) / HydroFlex: Replacement of hydrogen cartridge (pdf)
Manual for Mini-HydroFlex (pdf) / HydroFlex: Manual for HydroFlex (pdf)
Some deposits can be wiped off with a cloth.
For the Mini-HydroFlex, you can carefully sand the bottom of the electrode using 1000-grit sandpaper.
More stubborn contaminants dissolve in 1 mol/L nitric acid. The electrode must then be thoroughly rinsed in distilled water.
If necessary, you can perform a complete cleaning.
Cleaning of hydrogen electrode HydroFlex (pdf)
If the cleaning steps are unsuccessful, the electrode is unfortunately so badly contaminated that we recommend purchasing a new one.
Sometimes a complete cleaning of the HydroFlex is required – especially when there are visible deposits on the electrode.
Hydrogen production is very low (approx. 1 ml per day). Therefore, it is rare for hydrogen bubbles to become visible.
If the potentials are all right, the reference electrode is working. Check the potentials once a week or once a month against an Ag/AgCl electrode in a pH 2 or pH 4 buffer.
Note the necessary replacement of the hydrogen cells.
Mini-HydroFlex: Replacment of hydrogen cell (youtube) / HydroFlex: Replacment of hydrogen cartridge (youtube)
Mini-HydroFlex: Replacement of hydrogen cell (pdf) / HydroFlex: Replacement of hydrogen cartridge (pdf)
Manual for Mini-HydroFlex (pdf) / HydroFlex: Manual for HydroFlex (pdf)
For the transport the internal buffer of pHydrunio is removed. Open the red transport plug and use the provided syringe and cannula to insert about 5 ml of the provided inner buffer solution pH 7 into the pHydrunio.
Replace the red transport plug in the electrode head with the enclosed red pressure relief valve, which is also a screw cap.
pHydrunio only works with the delivered buffer!
The internal buffer (reference electrolyte) can also be replaced later. To do so, the sealing cap at the electrode’s head must be unscrewed. You can remove the internal buffer with the provided syringe and cannula. Rinse the electrode with distilled or deionized water. Fill in the new internal buffer directly from the vial. Screw down the pHydrunio carefully. Place pHydrunio in distilled water for 24 hours.
First, unscrew the red cap on the electrode head. Unscrew the two black caps on the electrode head’s side as well. Remove the hydrogen cells underneath. In the recess you see small O-rings. Please grease them both with silicone grease, for example.
Take the new hydrogen cells and remove the protective foil. Two openings become visible. If any adhesive residue remains, remove it by rubbing it with a cloth.
Place the hydrogen cells in the recesses with the openings facing down.
Screw the black caps back in. Screw the red pressure relief valve back into the electrode head.
Important: Mark month and year on the label. Attach the sticker to the electrode head. Place pHydrunio in distilled water for 24 hours.
First of all, the pH electrode is placed in calibration buffer pH 7. This determines the deviation from the zero point. Depending on the condition of the electrode, this may take several minutes. Note the measured voltage and the temperature of the buffer as soon as the voltage has become constant. Then, rinse the electrode and the temperature sensor with water before you place both in calibration buffer pH 4 or
pH 10. Here too, note the measured voltage and the temperature of the buffer as soon as the voltage has become constant. Waiting times of several minutes are possible.
After the measurements, rinse the hydrogen pH electrode thoroughly with water. Please place the pH electrode in a vessel with distilled water.
Under no circumstances should it be stored with the transport cap. The hydrogen would slowly squeeze the small volume of liquid out of the cap.
The hydrogen pH electrode should not be stored dry in air as long as the hydrogen cells are generating hydrogen. Otherwise, a mixed potential forms, which can lead to incorrect results. Pay attention to the runtime of the hydrogen cells.
You can check both electrodes in the hydrogen pH electrode separated from each other against a so-called master electrode, e.g. a calomel electrode. The master electrode should always be placed in an appropriate potassium chloride solution and not be used for any other purpose.
Pay attention to the fill level in the calomel electrode itself. It must always be above the fill level in the measuring vessel. Open the filling plug of your calomel electrode to prevent the measuring fluid from entering the calomel electrode.
To check the hydrogen pH electrode pHydrunio, place pHydrunio and the master electrode in buffer pH 0. Connect the calomel electrode to the positive pole. To contact the pH electrode, you need an appropriate adapter BNC to 4 mm laboratory socket.
Now, connect the red socket of the adapter with the negative pole (COM-port) of your voltmeter. You are now checking the outer measuring electrode of the hydrogen pH electrode. After an adjustment phase, which can last several minutes, you read off the potential.
Afterwards, connect the black socket of the adapter with the negative pole (COM-port) of your voltmeter. You are checking the inner reference electrode of your pH electrode. After an adjustment phase, which can last several minutes, you read off the potential.
It is assumed that the pH-values stay constant in these temperature ranges. Diffusion voltages are not considered.
Potential table for pHydrunio in calibration buffer pH 0 (pdf)
- Buffer solution
Please measure in fresh buffer solution. If buffer solutions are exposed to air for a longer period of time, the pH value may shift.
This occurs mainly with alkaline buffer solutions. - Slow ion exchange, e.g. when changing from concentrated solutions to weakly concentrated solutions
Please take the adjustment time into account, sometimes the balancing of concentrations takes longer than expected. If necessary, check the potential in another electrolyte, e.g. in calibration buffers. - Internal buffer contaminated
It can happen that measuring solution enters and contaminates the internal buffer.
In that case, the internal buffer has to be replaced. - Poor contacting
Check the measuring cables for optical damages such as corrosion, cracks, and sessile plugs. Replace the cables. Check both electrodes using an external reference electrode, e.g. a HydroFlex, calomel or silver silver chloride electrode. - Air/oxygen reaches the hydrogen electrode
Avoid that gases such as air or oxygen reach the platinum hydrogen electrode’s shaft. If this happens the hydrogen is displaced or reacts off. No hydrogen potential can be set. - No or insufficient hydrogen production
Has the runtime of the hydrogen cells been exceeded?
If yes, please replace the hydrogen cells.
- Hydrogen bubbles from the hydrogen electrode itself
Bubbles are continuously leaking out of the platinum 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. - 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.
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