Design Strategies for Alkaline Exchange Membrane-Electrode Assemblies: Optimization for Fuel Cells and Electrolyzers.

Production of hydrocarbon-based, alkaline exchange, membrane-electrode assemblies (MEA's) for fuel cells and electrolyzers is examined via catalyst-coated membrane (CCM) and gas-diffusion electrode (GDE) fabrication routes. The inability effectively to hot-press hydrocarbon-based ion-exchange polymers (ionomers) risks performance limitations due to poor interfacial contact, especially between GDE and membrane. The addition of an ionomeric interlayer is shown greatly to improve the intimacy of contact between GDE and membrane, as determined by ex situ through-plane MEA impedance measurements, indicated by a strong decrease in the frequency of the high-frequency zero phase angle of the complex impedance, and confirmed in situ with device performance tests. The best interfacial contact is achieved with CCM's, with the contact impedance decreasing, and device performance increasing, in the order GDE >> GDE+Interlayer > CCM. The GDE+interlayer fabrication approach is further examined with respect to hydrogen crossover and alkaline membrane electrolyzer cell performance. An interlayer strongly reduces the rate of hydrogen crossover without strongly decreasing electrolyzer performance, while crosslinking the ionomeric layer further reduces the crossover rate though also limiting device performance. The approach can be applied and built upon to improve the design and production of alkaline, and more generally, hydrocarbon-based MEA's and exchange membrane devices.