PolyFoleR: Compound bipolar foils for electrochemical reactors

Bipolar plates with carbon or metal-filled polymer compounds are in demand for applications in electrochemical reactors. In the project "PolyFoleR", a systematic investigation of different input materials of bipolar plates from the powder-to-roll manufacturing process patented by Fraunhofer UMSICHT is carried out. The main objective is to derive effective relationships between materials, processing and properties in order to enable rapid adaptation to changed requirement profiles. A particular focus is on increasing the mechanical stability of thin-walled polymer compounds. In this context, the introduction of fiber fillers as well as electron beam treatment are investigated as possible solutions. The developed materials will be extensively characterized and finally tested in single-cell experimental setups close to the application. Water electrolysis and PEM fuel cells serve as example applications.

The broad material screening and the development of a material library are also intended to create the basis for prospectively opening up the broad field of hydrogen technologies and other fields of application (e.g. electrochemical compressors, hydrogenation reactors, electrosynthesis cells or electrodialysis cells).

Whether electrolysers or fuel cells: Electrochemical reactors play a key role in a sustainable energy cycle based on hydrogen – especially with regard to production and storage. The update of the National Hydrogen Strategy has brought the topic up to date: In it, the German government formulates the goal of establishing hydrogen as an important energy carrier for the future and driving forward the decarbonization of the energy sector.

An essential component of electrochemical reactors is the bipolar plate. It is layered alternately with the catalytically active membrane and the gas diffusion layer to form a stack, which in turn forms the core of electrochemical cells. The bipolar plate is responsible for the electrical connection of the cells, the gas distribution by means of an inserted gas distribution geometry (so-called flow field) over the surface of the plate, the separation of the reactants between adjacent cells and the cooling of the entire system.

In order to perform these tasks both efficiently and over time, the bipolar plate must be resistant to the reaction media, oxidizing and reducing conditions, and have low permeability. It should also have high electrical and thermal conductivity, as well as high mechanical stability.

The foil-based compound bipolar plates of Fraunhofer UMSICHT combine the advantages of metallic plates ("thin, flexible and malleable") with the advantages of plastic compounds ("inexpensive and long service life"). At the same time, they avoid the respective disadvantages (expensive alloys, protective coatings, brittleness and high material thickness). In particular, the adjustable flexibility or stiffness qualifies the material for a wide variety of applications. In addition, the unique product properties such as formability, laminability and weldability open up new possibilities for stack design.

The findings from the "PolyFoleR" project are intended to help shorten the development cycles for bipolar foils from the powder-to-roll process. At the same time, they should enable targeted adaptation of the product properties to meet the specific requirements of different areas of application. This forms the basis for the targeted development of new fields of application such as electrochemical compressors, hydrogenation reactors, electrosynthesis cells, electrodialysis cells and bipolar batteries.

• identification of suitable input materials (binder polymer, graphite and metal powders, additives, etc.) for the production of the electrically conductive polymer compound foils with regard to the specific requirements of the respective target application
• evaluation of processability and process properties in the novel powder-to-roll manufacturing process
• experimentally validated material library
• optimization of material properties (electrical conductivity, mechanical properties, etc.) for use in electrolyzers and fuel cells
• evaluation of the performance of the developed materials in single-cell experimental setups (PEM FC and membrane electrolysis)

• Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP
• Schaeffler Technologies AG & Co. KG

The project "PolyFoleR – Electrically Conductive Polymer Compound Foils for Electrochemical Reactors" is funded by the German Federal Ministry of Education and Research (BMBF) as part of the ideas competition "Hydrogen Republic of Germany" Module 2 – Basic Research on Green Hydrogen.