Ein effektives Wassermanagement ist ein wichtiger Aspekt in der Entwicklung von Brennstoffzellen hinsichtlich Langzeitstabilität und Optimierung der Leistungsfähigkeit. Eine zentrale Rolle spielt dabei die Gasdiffusionslage, die für die gleichmäßige Verteilung der Reaktionsgase auf die elektrochemisch aktive Schicht (Katalysator) sorgen soll. In diesem Beitrag werden gemeinsame Forschungsaktivitäten des Helmholtz-Zentrums Berlin für Materialien und Energie (Entwicklung bildgebender Verfahren) sowie des Zentrums für Sonnenenergie- und Wasserstoff-Forschung (ZSW, Entwicklung von Brennstoffzellen) vorgestellt. Im Rahmen dieser Kooperation werden die Entstehung, die Verteilung und der Transport von flüssigem Wasser, kurz das Wassermanagement, unter Betriebsbedingungen untersucht. Mittels Synchrotronradiografie und -tomografie werden kleinste Wassercluster in der Gasdiffusionslage detektiert. Die gewonnenen Erkenntnisse dienen der Modifikation und einer gezielten Auswahl der eingesetzten Materialien.
Water transport in an operating PEM fuel cell was investigated with synchrotron X-ray radiography with a spatial resolution of 3 µm and a temporal resolution of 5 s. This method allows for the detection of water accumulations with less than 10 µm diameter. We demonstrate that synchrotron X-ray imaging can dramatically expand the possibilities of imaging with high spatial and time resolution, especially as a complement to neutron radiography. Water transport processes from the first appearance of small water accumulations in the gas diffusion layer to their transport into the channel system were analysed in situ. Correlations between local effects such as water formation and operating conditions of the whole system, e.g. power variations, were found. A recently described eruptive water transport mechanism is analysed in detail.
A new high-resolution detector setup for neutron imaging has been developed based on infinity-corrected optics with high light collection, combined with customized mounting hardware. The system can easily be installed, handled and fitted to any existing facility, avoiding the necessity of complex optical systems or further improved electronics (CCD). This is the first time optical magnification higher than 1:1 has been used with scintillator-based neutron detectors, as well as the first implementation of infinity corrected optics for neutron imaging, achieving the smallest yet reported effective pixel size of 3.375 µm. A novel transparent crystal scintillator (GGG crystal) has been implemented with neutrons for the first time to overcome limitations of traditional powder scintillators (Li6/ZnS, Gadox). The standardized procedure for resolution measurements with the Modulation Transfer Function (MTF) is summarized to facilitate comparison between instruments and facilities. Using this new detector setup, a resolution of 14.8 µm with a field of view of 6 mm × 6 mm has been achieved while maintaining reasonable count times. These advances open a wide range of new possible research applications and allow the potential for additional future developments.