K-002

Klaus-Dieter Kreuer

kreuer@fkf.mpg.de

Didem Yazili, Jules-Fabien Kreuer, Carolin Klose, Andreas Münchinger, Michael Schuster, Giorgi Titvinidze 

Hahn-Schickard and Max-Planck-Institute for Solid State Research, Germany

Rational Design of Hydrocarbon Proton Conducting Ionomers for PEM Water Electrolysis

220 years after C. J. T. de Grotthuss’ MÉMOIRE "Sur la decomposition de l’eau à l’aide de l’électricité galvanique” we are facing the challenge how to make the process discussed in Grotthuss’ paper more efficient, reliable and sustainable.

In PEM water electrolysis, perfluoro-sulfonic-acids (PFSA) such as Chemour’s Nafion® are commonly used as proton conducting membrane material and as binder in the electrode structures. Obvious reason for this are not only the facts that PFSAs are established ionomers for chlor-alkali-electrolysis, PEM-fuel cells and even redox-flow-batteries, but also the unique property profile of PFSAs. The extreme hydrophobic/hydrophilic contrast of their chemical structure and the way their PTFE backbone aggregate are related to their high proton conductivity, outstanding thermo-hydrolytic stability and moderate swelling in water. 

In contrast, most environmentally more friendly hydrocarbon alternatives are not stable under electrolyzer conditions. They also require higher degrees of sulfonation for obtaining similar conductivities, which come with significantly higher water uptake making them problematic as engineering material.

Here, we present a rational design approach towards new hydrocarbon ionomers: starting by down selecting chemical platforms with long term chemical stability as conditio sine qua non, we then demonstrate how small controlled changes of the sulfonation pattern of sulfonated poly (phenylene sulfones) sPPS affect backbone aggregation and with this also swelling in water. If done properly, reduced swelling is achieved without sacrificing solubility in aprotic polar solvents such as DMSO/DMAc from which sPPS ionomers are cast into membranes. With this approach, thin (20 micro-m) membranes were developed for PEM-electrolyzers and produced on a commercial production line.  Such membranes were then combined with electrode structures using sPPS as proton conducting binders in all hydrocarbon membrane-electrode-assemblies MEA and tested in water electrolyzers with very encouraging performance and durability results.

C. Klose, T. Saatkamp, A. Muenchinger, L. Bohn, G. Titvinidze, M. Breitwieser, K. D. Kreuer,  S. Vierrath: All‐hydrocarbon MEA for PEM water electrolysis combining low hydrogen crossover and high efficiency, Advanced Energy Materials 10, 1903995 (2019)

D. Yazili, E. Marini, T. Saatkamp, A. Münchinger, G. Titvinitze, M. Schuster, C. Schare, L. Jörissen,  K. D. Kreuer: Sulfonated Poly (Phenylene sulfone) blend membranes finding their way into proton exchange membrane fuel cells, Journal of Power Sources 563, 232791 (2023)