| AVS 59th Annual International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Thursday Sessions |
| Session EN+NS-ThM |
| Session: | Batteries and Fuel Cells |
| Presenter: | A.M. Herring, Colorado School of Mines |
| Correspondent: | Click to Email |
Proton exchange membrane (PEM) fuel cells are still the most desirable component of future zero emission, high efficiency automobiles fueled with hydrogen. However, their unit cost, ease of operation, and reliability must be reduced which includes eliminating the humidifier from the fuel cell system. Currently the commercial PEM is fabricated from a perfluorosulfonic acid (PFSA) polymer such as Nafion®. Unfortunately PFSA ionomers must be fully hydrated to achieve practical levels of proton conductivity which can only be achieved in vehicles operating at an inlet RH of 85% which still necessitates the use of a humidifier and undesirable complex water management and recovery. To achieve the goal of a PEM that can operate at temperatures from freezing to 120ºC using dry inlet gases it will be necessary to develop new PEMs that are based on new chemistries or dramatically improved morphologies of existing chemistries. The versatility of the polymer electrolyte fuel cell could be expanded to more complex fuels with the use of an anion exchange membrane (AEM). An AEM fuel cell could potentially utilize less expensive metal catalysts and have the ability to oxidatively cleave carbon-carbo bonds.
Ionomers are generally perceived as being phase separated materials. However, the optimal morphology that an ionomer should adopt and that would be practical is still being debated. This situation is not helped by the uncertainty of the morphology adopted under operating fuel cell conditions of the incumbent material. Here I will describe a study that contrasts fully amorphous materials with materials designed to have phase separated morphologies of known symmetries and dimensions. While the designed materials allow us to probe certain consepts of ion conduction with pore shape and size, they do not necessarily out perform the amorphous materials. Curiously we show that the role of water has more to do with morphological changes in flexible materials than enhancing ion conduction in non-sulfonic acid based materials. This has implications for the fabrication of thin robust films that will be needed for an operating fuel cell. In the case of AEMs while a cation has yet to be found that is stable under hot and dry operation, water may be a necessary evil rather than an enhancer of anion conduction.