08 May 2026
The generation of green hydrogen by water electrolysis represents an exciting decarbonisation opportunity. However, the performance of electrolyzers is heavily impacted by the characteristics and stability of the electrolyzer’s components. A group of engineers in Germany is developing a test bench for alkaline electrolysis.
A key factor affecting the success of this project is the ability to accurately and reliably monitor electrolytes in an extremely aggressive solution. Following a global search for suitable technologies, the researchers identified that Vaisala’s inline refractometers were able to meet their stringent requirements.
The project partners are the engineering services provider iChemAnalytics GmbH, the electroplating technology specialist Dr.-Ing. Max Schlötter GmbH & Co. KG, and the coating expert WHW Hillebrand.
As the world seeks to decarbonise its energy infrastructure in pursuit of a Net Zero goal, hydrogen represents an exciting opportunity. Hydrogen has a high calorific value and its combustion products do not contain any greenhouse gases that are considered major contributors to global warming. However, hydrogen is currently mostly produced from fossil-fuel intensive processes, generating ‘grey hydrogen’ which globally accounts for around 2% of carbon emissions.
Where hydrogen is generated from the electrolysis of water, powered by renewable energy, the resulting ‘green hydrogen’ offers a significant opportunity for decarbonisation, so there is a high level of interest in efficient, sustainable electrolyzers.
Alkaline hydrogen electrolyzers use an electric current to split water into hydrogen and oxygen using a liquid alkaline solution such as potassium hydroxide (KOH) as the electrolyte. Typically, the solution is 15 to 30% KOH, which is very aggressive. The electrolyte is contained between two electrodes – typically nickel-based – separated by a porous diaphragm or membrane. Hydrogen gas is produced at the cathode, and oxygen gas is produced at the anode. The diaphragm separates the gases and transports hydroxide ions from the cathode to the anode to complete the circuit.
The main objectives of the project were to create a working, fully automated test bench for electrolyzer stacks; develop a new electrode coating which is stable for over 80,000 hours; and evaluate prototype coatings over a range of different working conditions.
Each side of the membrane in the test bench electrolyzer contains a 30% KOH solution – a highly concentrated, strong, and corrosive alkaline liquid that is 30% potassium hydroxide and 70% water by weight. During electrolysis the ratio of KOH % on either side of the membrane changes. This is important for multiple reasons. The service life of the components and the phase boundary reactions within the cells change negatively, which also has a direct influence on cell voltage, aging effects and reaction efficiency.
Electrolyte measurement
The project team conducted a worldwide search for a technology that would be able to operate in such a challenging environment, delivering accurate and reliable KOH measurements. The ability to operate in 30% KOH at temperatures up to 80°C and pressures up to 5bar (mounted in-line) ruled out most options, leaving either manual laboratory analysis or a small number of technologies based on refractometry or ultrasonics.
Explaining the decision to use Vaisala’s inline refractometers, Kristian Macke COO at iChemAnalytics, said: “Laboratory analysis was ruled out immediately because of the time taken to derive results, which would render process control, and therefore efficiency, impossible to achieve.” The project team evaluated the continuous measurement options. “We were particularly impressed by the support from Vaisala’s distributor, Bühler Technologies. They lent us a Vaisala refractometer so that we could conduct a quick test in our laboratory. They provided CAD files to help integrate the device into our test bench, and they provided written confirmation that the refractometer is resistant to KOH permanently,” continued Kristian.
Two Vaisala inline refractometers have been installed on the test bench, providing real-time KOH concentration measurements on both sides of the membrane. Kristian says: “This was a significant investment for us, but we are pleased with the performance of the probes. They were delivered factory-calibrated and were almost plug-and-play. All we had to do was integrate their 4-20 mA output with our PLC,” said Kristian.
The refractometers measure the angle of refraction of light in the process medium, using an LED light source. A sensor continually detects the critical angle at which the total reflection of light commences, and this has a direct relationship with KOH concentration.
In addition to their ability to operate in harsh conditions, one of the main advantages of the chosen refractometers is that they are not affected by suspended particles, bubbles or colour, and with the option of automatic prism wash with steam or high-pressure hot water, they are not affected by scaling or fouling.
Project progress
The development of a reliable test bench has allowed the project team to focus on the main objectives. Different electrode coatings and electrolyte solutions are undergoing accelerated stress testing in a range of temperatures.
As more sustainable coatings are being developed, the new fully automated test bench will allow the team to optimise electrolysis equipment, materials and conditions in the pursuit of process efficiency. “KOH concentration measurement with the refractometers is performing a critically important role in the test bench,” concluded Kristian. “Clearly, the ultimate goal is to develop high-performance electrolyzer stacks with high-performance surface coatings, and the ability to automatically monitor and control the KOH ratio will be essential for optimising electrolyzer components and efficiency.”
