Einfluss der klimatischen Fertigungsumgebung auf die Mechanik und Rissstrukturierung der elektrodenbeschichteten Membran einer PEM-Brennstoffzelle
Jülich / Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag (2019) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (IV, 141 Seiten) : Illustrationen, Diagramme
Due to the imminent launch of the first European fuel cell vehicle by the Daimler AG, the production process of the catalyst coated membrane (CCM) has taken the transition from the development phase to the serial phase. As an integral part of this transition, the analysis of a fluctuating climate environment in manufacturing as well as an uneven web tension of the continuous production process represent the motivation of this work. The constitution and conformation of the polymer components of two different CCM systems determine their mechanical dependence to hydrothermal main effects and interactions. The quantification of these hydrothermal dependencies is carried out by a dynamic mechanical analysis (DMA) based on a non linear design of experiment (DOE). In a first step of method development, the sample geometry, the stimulation amplitude and the heating rate of the DMA measurement tool have to be adapted to the viscoelastic CCM systems. Following this, a measurement program is adapted to the factor combinations of the DOE in a second step. As a result, the storage and loss moduli show a negative main effect of temperature and a positive main effect of the relative humidity with respect to both CCM systems. A linear length variation of the reference CCM up to a relative humidity of 80% takes place independently of temperature and is confirmed by the literature. For the derivation of a climate-dependent, maximum tensile force on the CCM, a test set-up consisting of a mechanical and optical unit in a climate chamber is built. The mechanical stretching of CCM samples creates crack structures which can be quantitatively evaluated by digital image processing. In the relevant method development the intensity spectra of the image, high and low-pass filtering as well as a threshold sensitivity were analyzed. The negative behaviour of the loss module due to an increase in temperature can be confirmed of both CCM systems. The initiation of cracks on the anode and cathode surfaces as well as the subsequent phases of the crack growth are subject to hydrothermal influences. Thus, the cathode-side crack initiation decreases with increasing relative humidity, while the anode-side crack initiation shifts to higher elongations with increasing temperature. In sum maximum tensile forces can be specified by linking anode-side crack initiations and thermally dependent force measurements. Due to quantitative and qualitative results of a mechanical and electrochemical degradation program in this work, cracks on the electrode surface can’t other than considered as a "useful tool". Up to 8,000 humidity cycles, no cracking structures in the membrane boundary layer or an increased hydrogen permeation can be observed. Even a shift of the mass transport loss to higher current densities and an increase in power density was shown for the cracked MEAsample at the beginning of an electrochemical degradation program.
Lehnert, Werner Karl Josef