Durability issues of the PEMFC GDL and MEA under steady-state and drive-cycle operating conditions
- David L.
- Jian
- Susan D.
- John R.
- Rodney L.
Component durability remains, in most cases, a prohibitive barrier to widespread commercialization of stationary and automotive PEMFC systems. Aspects of this topic are difficult to quantify and improve not only because of the quantity and duration of testing time required (i.e., up to several thousand hours or more), but also because the fuel cell stack is a system of components (electrocatalysts, membranes, gas diffusion media, bipolar plates, and gaskets) for which the degradation mechanisms, component interactions, and effects of operating conditions are not fully understood. Simply acquiring 5000 hours of durability test data on a fuel cell stack or single cell will not lead to a comprehensive understanding of the degradation mechanisms. The individual components must be well-characterized during durability testing to determine and quantify degradation mechanisms that occur over long periods. Chemical degradation mechanisms in an operating environment are likely interconnected due to trace compounds that leach out of one component and subsequently affect another. For this reason, the separate degradation characteristics of each individual component must be well understood. This study focuses on fundamental durability understanding of two key stack repeating units, the membrane electrode assembly (MEA) and gas diffusion layer (GDL). Little has been published in this area, as most of the historical emphasis has been on stack or component performance improvement (i.e., beginning of life or short-term data). In this work it is desired to develop an initial basis for transitioning the emphasis towards understanding longer-term (1000-5000 hours) behavior of existing technologies, rather than the more common model of continual next-generation technologies based on only a few 10's or 100's of hours of data. Even though a given stationary application may have multiple power set points, it will operate nearly all of the time at a given set point. Therefore, the important design considerations should reflect steady-state operating conditions, where the cell temperature, gas flows, voltage, current density, etc., will be maintained for many hours at a time. Automotive applications on the other hand, will require continual changes in load, which may require many system set points to respond simultaneously. Despite the drastic difference between automotive and stationary lifetime targets for PEMFC stacks (5000 vs. 40,000 hours, respectively), the transient effects of continual changes in power set point may induce significantly more aggressive degradation conditions on the MEA and GDL materials. Thus, life testing of single cells is carried out at a given set point to simulate stationary applications and as a drive cycle with continuously varying cell power to simulate transportation applications, which yields information about how a given component will behave under appreciably different operating characteristics.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 977792
- Report Number(s):
- LA-UR-04-5369; TRN: US201012%%729
- Resource Relation:
- Conference: Submitted to: Fuel Cell Seminar, November 2004, San Antonio, TX
- Country of Publication:
- United States
- Language:
- English
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