Controlling hydrophilic channel alignment of perfluorinated sulfonic acid membranes via biaxial drawing for high performance and durable polymer electrolyte membrane water electrolysis

This study focuses on improving performance and durability of perfluorinated sulfonic acid (PFSA) membranes for polymer electrolyte membrane water electrolysis by controlling the membrane microstructure. To replace the highly gas permeable and expensive PFSA membranes, a membrane with low gas permeability and ohmic resistance is required for the high performing and safe water electrolyzers. Here, a thick PFSA membrane, Nafion 117 is biaxially stretched up to 6.4 times to reduce the membrane thickness, and increase the hydrophilic channels’ tortuosity. The thinned and planarly stretched Nafion shows better cell performance and durability at a constant current than the thick Nafion due to the reduced ohmic resistance and the enhanced interfacial stability between membrane and catalyst layer. With more tortuous hydrophilic pathways of the stretched Nafion, hydrogen permeability is reduced by a factor of 1.6, which is beneficial to prevent the membrane degradation and also to widen the operating current density range. The current density at 1.9 V increases from 1.5 to 3.2 A/cm2 after stretching, and the biaxially stretched membrane shows 4 times lower enhancement in ohmic and cathodic charge transfer resistance than the similarly thick Nafion after the constant current experiment, yielding 2.5 times lower degradation rate.