Rational Design of Hydrocarbon Proton-Conducting Membranes Replacing Perfluorosulfonic Acids in Polymer Electrolyte Membrane Water Electrolysis

High Resolution Image Download MS PowerPoint Slide Contrasting the characteristic properties of PFSAs such as Nafion and hydrocarbon membranes suggests that PEM water electrolysis could become a first showcase for the competitive use of hydrocarbon membranes. The main reasons are high proton conductivity and low hydrogen permeability of many sulfonated polyarylenes and phenylenes under water electrolysis conditions. Within this class of ionomers, we have, therefore, downselected according to thermohydrolytic stability, a conditio sine qua non for the use of membranes in PEM electrolyzers. We identified the family of sulfonated poly(phenylene sulfones) (sPPS) as virtually inert hydrocarbon ionomers. The remaining critical issues of sPPS membranes, especially exaggerated swelling at high ion exchange capacity, softening in hot water ( T = 80 °C) and fatigue under wet/dry cycling conditions, were significantly mitigated by (i) introducing into the homogeneously (ordered) sulfonated polymer structure uniform unsulfonated segments aggregating into well-connected networks counterbalancing osmotic pressure and (ii) introducing ductile polyethylene nanoporous reinforcements serving as fracture toughener. The present rational design approach provided the basis for successful in situ electrolyzer tests of 24 μm thick sPPS-based membranes published in a separate paper. This features lower ohmic losses along with a more than 2-fold reduced hydrogen crossover compared to Nafion 211 and stable operation over 2000 h at a current density of 1 A cm –2 without failure to the end of the test.