(639a) Accelerated Membrane Chemical Degradation and Diagnostic Methods

The key metrics in determining applicability of a polymer electrolyte membrane (PEM) to automotive fuel cells are performance and durability. Durability screening of candidate membrane materials is particularly challenging, as PEMs for automotive applications are required to last for 5500h in a dynamic environment over a range of operating conditions. A key challenge is to develop accelerated tests and diagnostics that enable rapid screening of potential membrane candidates without consuming exorbitant time and resources. These tests must also provide understanding of the mechanisms by which the membranes fail in order to enable appropriate material improvements. PEMs generally fail due to chemical and/or mechanical degradation. General Motors has developed accelerated testing methods and diagnostic tools to elucidate the specific membrane degradation mechanisms and to screen potential PEM candidates for automotive applications. The various diagnostics are performed in-situ to determine the relative health of the membrane sample. These diagnostics include measurements of fluoride release rate, voltage, hydrogen takeover, shorting, and crossover. These in-situ diagnostics are validated with ex-situ post-test membrane thickness measurements and failure analysis. Accelerated chemical degradation tests have been performed for several commercial perfluoro sulfonic acid (PFSA) PEMs. Minimum durability requirements are suggested for potential applicability to fuel cell automotive applications.