Ionomer thin films for fuel cells and related applications

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Polymer thin films with dimensions less than one-thousands the size of human hair behave differently than their bulk material counterpart. Conducting polymers are sub-class of this material group and depending on the molecular architecture, they can be either electron-conducting or ion-conducting. Thin films of ion-conducting polymers or ionomers find a variety of applications, e.g. in fuel cells, artificial photosynthesis, sensors, actuators, and as functional coatings. The ionomer thin films in the catalyst layers of polymer electrolyte fuel cells (PEFCs) have been identified as a source of significant performance/voltage loss due to unexpectedly high mass transport resistance. Overcoming this problem is now considered critical to making the PEFCs affordable, if we are to harness its potential as zero-emissions power source for urban vehicles. The answer to the problem is designing next generation ionomer materials that possess facile mass transport characteristics. However, the lack of relationship between ionomer molecular structure and its properties is hampering the design and development of such materials. In the proposed research will use a science-based approach for unraveling the origin of the mass transport resistance some advanced experimental techniques - one of which has only recently become available in whole of North America - the Positron Beam Facility at McMaster University, Canada. ******The long-term objective of the proposed research program is to guide the development of new ionomer molecules tuned for application-specific functionalities, e.g. in fuel cells, artificial photosynthesis, sensors, actuators, coatings, nanothin selective membranes. This will be achieved by establishing structure-property relationships of ionomer films, quantifying how the phase-segregated structure and resulting properties responds to pertinent stimuli (temperature, humidity, potential), and link it all to the molecular architecture of ionomer and its interactions with substrates varying in chemical/ physical characteristics. By studying a number of different ionomer varying in their molecular architecture, the research program will link the molecular architecture of the ionomers to the film structure-property. Such a knowledge currently does not exist. The fundamental knowledge created from the research program will provide science-based guidelines for the design of next-generation ionomer materials tuned for desirable functional properties; e.g. ionomers with high free volume, i.e. enhanced mass transport characteristics for PEFCs; ionomers with highly hydrophilic interfacial surface for facile sorption of polar molecules (e.g. alcohol) for sensor applications; ionomer films with hydrophobic surface for water-repellant protective coatings. Knowledge on substrate-ionomer interaction will benefit nanofabrication based on thin film platform.