OPCELMES – Optimal cell design, flow dynamics and current control for MW electrolyser systems

Challenge
Green hydrogen production is regarded to be one possible way to mitigate volatile renewable energy production and to be capable of reducing the CO2 emission in society.

Right now, four technologies are being discussed to become future grid connected electrolysers:

• PEM (Proton Exchange Membrane)
• Solid Oxide
• Alkaline electrolysers
• Pressurised Alkaline electrolysers

All four technologies have pros and cons, and it is right now not clear which technology is the best one for grid connected electrolysers.

The state-of-the-art commercial minimum power consumption is in the order of 55 kWh/kg H2. The theoretical limit is approx. 40 % lower. There is hence still an enormous potential of improvement.

Right now, alkaline electrolysers represent the most cost-effecient technology of state-of-the art MW electrolysers, while pressurised alkaline offers the additional advantage of providing pressurised hydrogen and being more compact. Therefore, the project concentrates on alkaline and pressurised alkaline electrolysers.

There is an inadequate fundamental understanding of the parameters influencing stack performance, e.g., geometry inside the stack such as electrode shape to reduce resistance and allow bubble formation and release and the dynamics of the interaction of the power electronics with the electrochemical, thermodynamical and hydrodynamical systems. Developing this understanding is crucial to reach optimal performance of future converter – electrolyser systems.

The future converter shall have an optimized current control to produce more hydrogen related to used input power. The new converter technology shall also become more robust versus grid failures when the dynamics of the overall system is understood.

The research shall further lead to an overall improved understanding of the reliability and lifetime of the electrolyser systems.

One important aspect of the electrolysis process is the hydrogen gas bubble forming and its transportation out of the cell. The bubbles act as dynamic impedances (change of resistivity of the electrolyte) and therefore disturb the current flux in the electrochemical cell itself. To improve the hydrogen production the flow of hydrogen during the electrolyzing process must therefore be understood and improved.

Solution
The objectives of the project are:

• A better fundamental understanding of stack performance to enable optimization and enhance the coupling to the converter
• Investigation of the impact of surface structure elements of electrolyser stack electrodes and separators of alkaline electrolyser on the dynamics of hydrogen production in connection with electrolyte injection into the stack and current feed of the power converter and development of a lab prototype
• Development of improved feeding DC (or pulsed DC) current control of the power converter for the electrolyser stack electrodes leading to novel converter designs and their control strategies
• Overall, the ambition is to reach a significant improvement in the order of minimum 5 percent in efficiency in respect to state-of-the-art hydrogen production.

Expected result/effect
The targeted Technology Readiness Level (TRL level) in this project is 6 starting at level 4 and the targeted converter technology can be realized in less than 3-5 years for market launch. Electrolyser stack development will continue beyond this horizon.

Problem owner

• Danfoss

Problem solver

• University of Southern Denmark
• Green Hydrogen Systems