Towards Solving Fundamental Issues For Alkaline Exchange Membrane Fuel Cells

摘要

Anion transport in polymer exchange membranes is important to fuel cells that have the potential to revolutionize energy conversion. However, anion transport is still poorly understood in terms of its relationship to water content, morphology and chemistry. While a large amount of research has been performed for proton exchange membranes, little work has been performed with anion exchange membranes. These systems are particularly interesting in that the charge carrier may be hydroxide, or carbonate. It is not sufficient, however, to simply understand anion transport in these systems, as robust thin films that have high ionic conductivity must also be fabricated for practical applications. We are synergistically developing new polymer architectures with standard and novel cations. The synthetic work is iteratively preparing stable cations, varying modes of attachment to polymer backbones, and generating controlled morphologies. Synthesis and characterization are tied closely to theory through model validation, firstly by the study of aqueous solutions of representative cations and secondly by the study of well-defined polymer architectures. We use a predictive multi-scale computational approach to probe both anion transport and its coupling to polymer morphology. At the molecular-scale a generalization of a novel reactive molecular dynamics methodology is being developed, while more statistical characterizations of ion transport is implemented on the scale of the membrane thickness. The novel films are studied in terms of the anion species present, their transport and equilibria. Water content is measured by dynamic vapor sorption. Bulk transport is studied in an accurately controlled temperature and relative humidity. This is complemented by the measurements of self diffusion coefficients and molecular scale activation energies by NMR. Extensive state of the art mechanical and rheological, testing is used to develop robust thin films. Morphology is related to film mechanical properties through state of the art measurements and film degradation will be studied in depth.