Interlocking Membrane/Catalyst Layer interface for High Mechanical Robustness of Hydrocarbon Membrane Based PEMFC

Abstract

For decades, the use of hydrocarbon ionomers in PEMFCs has been constantly attempted as a membrane to replace the commonly used perfluorinated ionomers to lower costs, raise fuel efficiency, and enable easier manufacturing of membrane electrode assembly (MEA). Examples include sulfonated poly(arylene ether sulfone)(s-PAES), sulfonated poly(ether ether ketone) (s-PEEK), and sulfonated polyimide (s-PI). However, when a hydrocarbon membrane is assembled with catalyst layers (CLs) based on a perfluorinated ionomer, a problem of interfacial delamination between the membrane and the CL is often encountered. Due to the poor interface between hydrocarbon ionomer based membrane and perfluorinated ionomer based catalyst layer, in many cases, opportunities to be employed in PEMFC have been denied.To address this problem, hydrocarbon ionomers having chemical structures similar to those of the membrane have been introduced as proton conducting polymer electrolytes into CL. However, due to the low oxygen permeability of the hydrocarbon ionomers, the corresponding CL showed a relatively low power performance. Although such tight interfacial bonding for hydrocarbon membranes has been urgently requested, the problem still remains unsolved. Here, we propose an interlocking interface structure for providing a tight interfacial bonding between hydrocarbon membrane and perfluorinated ionomer based CL, turning away from the previous focus on chemical modification and physical roughening. This approach is based on a friction force generated due to a difference in volume expansion between the two polymers in an interlocked architecture. The interlocked interface of sulfonated poly(ether ether ketone) and Nafion based CL were realized and evaluated. A profound improvement in interfacial bonding strength was observed with the interlocked architecture. Also, under accelerated stress conditions, interfacial bonding was better maintained with the interlocked interface. The physical interlocking strategy could provide an oppotunity for a lot of hydrocarbon membrane suffering from poor interfacial adhesion to be used in PEMFC.