(Invited) Membranes for Alkaline Water Electrolysis

Hydrogen production through water electrolysis has attracted renewed interest in converting low-carbon electricity into hydrogen in the last few years. The so-produced hydrogen can be used as a reagent for the chemical industry, as a fuel, or for long-term storage of excess renewable energies, contributing to reducing CO2 emissions in many sectors. The most mature and commercially available technology developed for hydrogen production is alkaline water electrolysis (AWE), where nickel-based electrodes are exploited as an anode and cathode and are immersed in concentrated KOH electrolyte (5-6 M). Proton exchange membrane water electrolysis (PEMWE) is also a commercially available technology that exploits ion exchange membranes. Platinum and iridium are exploited as the cathode and anode catalysts and are deposited directly on the ion exchange membrane, while pure water is fed to the system. Replacing the current AWE diaphragms with ion exchange membranes can improve the performance in terms of cell resistance and gas crossover, similar to PEMWE. This relatively new technology, called anion exchange membrane water electrolysis (AEMWE), has recently gained good attention. The common feature among all the above-mentioned technologies is using a flow cell and a membrane within to separate the anode and cathode. The membrane is significant in terms of output power and capital costs of the system. In this presentation, the membrane function in water electrolysis flow cells will first be explained, together with the most significant parameters influencing the system's performance. Next, the main focus will be on AEMWE systems using sustainable flourin-free ion exchange membranes. The research questions will be answered: What is the ideal membrane? And how does membrane and membrane-electrode assembly (MEA) influence the AEMWE performance? Also, the results of a new study we have done in collaboration with Lund University will be shared. A newly synthesized membrane, the poly(fluorene phenylpropylammonium) (PdF-TMA) was proposed for high electrolyte concentration. The performance of AEMWE was compared with a case using a commercial benchmark membrane (AEMIONTM). Increasing the electrolyte concentration improved electrode kinetics but with different effects on the membranes. PdF-TMA was quite stable during operation as its resistance did not increase. On the other hand, the AEMIONTM lost conductivity and stability when operated in 2 M KOH.