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Electrolysis & Power-to-X
The discovery of electrolysis was basically made possible by the “invention” of the battery, which can largely be traced back to Alessandro Volta. While the processes in the battery remained misunderstood for a long time, electrolysis provided the possibility to understand electrochemical processes better and better.
What is electrolysis and how does it work?
Electrolysis is the conversion of electrical energy into chemical energy when the current forces a redox reaction and thereby triggers a chemical process.
At the cathode electrons are “transported” from the electrode into the solution. If positively charged ions (cations) are in the solution, they can migrate to the cathode and take up electrons there, i.e., be reduced. At the anode, electrons flow “back” into the external circuit. Here, negatively charged anions or neutral particles are oxidised.
In electrolysis, n electrons are “pumped into” the solution with an external current source. The same amount of electrons must be “extracted” from oxidisable particles in the solution at the anode. All this only works if the circuit in the solution is also closed by the migration of ions between the two electrodes. The solution must therefore be an ion-conducting medium, an “electrolyte”. To prevent the products from mixing, the reaction spaces are often separated by a diaphragm.
Electrolysis is therefore a means of significantly accelerating sluggish reactions by applying a sufficiently high overvoltage without requiring high temperatures.
Research & development is currently focussing on high-tech solutions that reduces energy consumption and CO2 emissions as sustainably as possible. This is being attempted through the following approaches.
- Catalytically active and corrosion-free electrode materials
- Galvanostatic electrolysis to make the reactions more selective and generate less waste
- More efficient use of energy by pairing the electrode processes
Increased surface area through a three-dimensional electrode structure (foams or grids)
Achieving the highest possible currents
For optimisation of electrolysis parameters and material screening, we offer high precision potentiostats/galvanostats from PalmSens, Ivium und Origalys. For simultaneous high-throughput measurements, multi-channel systems such as the MultiPalmSens4, MultiEmStat4 (PalmSens), OctoStat and IviCycle (Ivium) are suitable. With optional boosters, higher current ranges up to 128A are also covered.
To gain insight into the nature of surface coatings or membranes, most of the instruments we offer are already equipped with an impedance module or can be retrofitted if required.
For reproducibility, the use of electrochemical cells with well-defined specifications such as electrode spacing, cell geometry and temperature control is also very important. The cells from ItalSens, Origalys, PalmSens (BASi) meet these high requirements, e.g., the ASTM standards (American Society for Testing and Materials).
Which processes are used for water electrolysis?
The classical alkaline electrolysis is carried out in diluted potassium hydroxide solution as electrolyte, the reaction chambers are separated by an inorganic diaphragm. The process is technically very mature, reliable and cost-effective. Unfortunately, they cannot be operated at partial load, as is necessary when feeding renewable energy into the grid.
In solid electrolyser cells (SOECs), the electrolyte is a solid that is ionically conductive at 500 - 850°C. The ability to use waste heat and therefore less electricity per kg H2 makes the process very suitable for chemical and industrial applications. Theoretically, the highest efficiencies can be achieved with SOECs.
Instead of salt solutions, thin, (almost) gas-tight membranes made of thermoplastic material (ionomer) are used as electrolytes. These Polymer Electrolyte Membranes (PEM) are either proton-conducting or also anion-conducting (AEM). Fig. 2 shows the functional principle of a water electrolysis cell for the production of hydrogen.
Principle of PEM electrolysis:
The catalytic electrode layers are deposited on the polymer membrane. The bipolar plates and gas diffusion layers serve for the electrical contact and the transport of water and product gases. At the anode, the water is oxidised to oxygen and protons. The polymer membrane is permeable for protons, therefore enabling charge transport, but not for gases. The protons pass through the membrane to the cathode and are reduced to hydrogen. Both gases or only H2 are collected and purified separately.
Electrolysis stack consisting of a large number of individual cells
For industrial-scale production, several such cells have to be stacked in so-called “stacks”.
The efficiency of PEM electrolysers is in the range of 70% and is also very high in partial load operation, which is why they are currently being intensively researched. In addition, they can react quickly to the fluctuating power input from renewable energy sources.
Challenges in water electrolysis
Research continues to increase the efficiency of all components:
- Catalyst loading and material requirements
- Water and gas transport, heat dissipation
- Electrical contact
- Corrosion resistance, durability and conductivity of polymer membranes
With test benches by Scribner and MaterialsMates, EKTechnologies provides optimal instruments in the power range between 100W and 100kW. With its sophisticated concept and extensive accessories, the 600 ETS by Scribner has become a standard in basic research and upscaling. Scribner has also set the standard with the extremely user-friendly FlowCell-ETS® software for planning and displaying experiments, and the ZView® EIS analysis software.
The engineers at MaterialsMates are able to tailor electrolyte test benches for upscaling to 100kW for specific customer needs. These can be equipped with the unique high-performance multi-channel system MM580-S for simultaneous impedance measurement up to 100kW and > 120 channels.
The systems are equipped with extensive safety mechanisms. In addition to systems for gas management, temperature control and humidification of the gases, our portfolio also includes electronic loads, potentiostats/galvanostats and impedance measurement systems. A comprehensive safety concept, careful instruction and continuous support are a self-evident part of our service.