Maren Rastedt

Effect of compression on the performance of a HT-PEM fuel cell

This paper shows by thorough electrochemical investigation that (1) the performances of high-temperature polymer electrolyte fuel cell membrane electrode assemblies of three suppliers are differently affected by compressive forces. (2) Membrane thickness reduction by compressive pressure takes place less than expected. (3) A contact pressure cycling experiment is a useful tool to distinguish the impact of compression on the contact resistances bipolar plate/gas diffusion layer (GDL) and GDL/catalytic layer. A detailed visual insight into the structural effects of compressive forces on membrane and gas diffusion electrode (GDE) is obtained by micro-computed X-ray tomography (μ-CT). μ-CT imaging confirms that membrane and GDEs undergo severe mechanical stress resulting in performance differences. Irreversible GDL deformation behavior and pinhole formation by GDL fiber penetration into the membrane could be observed.

Characterization of HT-PEM Membrane-Electrode-Assemblies

This chapter describes the most commonly used electrochemical measurement techniques to characterize HT-PEM membrane electrode assemblies (MEAs). Moreover, it will be shown what kind of information can be subtracted from each technique in order to provide a correct diagnosis of the HT-PEMFC behavior. Detailed descriptions of test procedures and methodology routines for each one of the electrochemical techniques are important for the comparison of data between different working groups is not always possible, thus leading to the need of standardized test protocols. The described test procedures and routines have already been verified in two European Projects. Micro-computed tomography X-ray technique has been introduced as a rather new post-mortem three-dimensional imaging method of the specimens under investigation. Therefore, μ-CT imaging enables the nondestructive characterization of usually hidden interfaces in HT-PEM MEAs that cannot be done by conventional microscopy techniques. MEA contact pressure plays an important role for degradation of MEA materials that can affect performance and lifetime of the HT-PEMFC. Thus, electrochemical and ex situ imaging techniques have jointly been used to investigate the effect of contact pressure increase as well as contact pressure cycling to verify the state-of-the-art of HT-PEM technology in different commercial MEAs. The importance to define long-term test routines will be discussed in the last section of this chapter. Long-term testing should reproduce real operation conditions and determine the issues to identify, understand, and minimize degradation mechanisms that limit the applicability of HT-PEM technology nowadays in systems ready for the market.