September 22, 2017
Speaker: Roswitha Zeis
Affiliation: Helmholtz Institute of Ulm
Location: MC 102
Date and time: September, 22, 2017, 2-3 PM
Fuel cells are among the enabling technologies toward a safe, reliable, and sustainable energy solution. Yet the lack of clean hydrogen sources and a sizable hydrogen infrastructure limits the fuel cell applications today. Due to their elevated operating temperature, between 150°C and 180°C, the high temperature proton exchange membrane fuel cells (HT-PEMFCs) based on phosphoric acid doped polybenzimidazole (H3PO4/PBI) membranes can tolerate fuel contaminants such as carbon monoxide (CO) and hydrogen sulfide (H2S) without considerable performance loss. It allows the HT-PEMFC to run on hydrogen produced on-site by reforming hydrocarbon fuels. The higher operating temperature also drastically simplifies water and heat management of the fuel cell (humidification not required in HT-PEMFCs) allowing a simpler system layout compared with a conventional PEMFC.
One of the group’s core competences is the development of high temperature membrane electrode assemblies (MEAs). To characterize our home-made MEAs, we generally apply impedance spectroscopy. The measured spectra are then analyzed by Distribution of Relaxation Times (DRT) method. Thereby, polarization losses can be separated on the basis of their typical time constants. The main features of the distribution function can be assigned to the cell’s polarization processes by selecting appropriate experimental conditions. DRT is used to identify individual internal HT-PEMFC fuel cell phenomena without any a-priori knowledge about the physics of the system. This method has the potential to further improve EIS spectra interpretation with either equivalent circuits or physical models .
Furthermore we investigate the distribution of phosphoric acid in the Gas Diffusion Electrode (GDE) of a HT-PEMFC. A GDE composed of a catalyst layer, Micro-Porous Layer (MPL), and fibrous substrate (GDL) was prepared and its three-dimensional (3D) geometry was imaged using synchrotron X-ray computed tomography. The spatial distribution of pore spaces and their connections were identified based on the 3D geometry, and an equivalent pore network of the GDE was obtained for simulating the phosphoric acid transport with an invasion percolation algorithm. The predicted mass redistribution of phosphoric acid in the GDE is in excellent agreement with experimental values reported in the literature . Our analysis spreads clarity on the role of the MPL in HT-PEMFC: the MPL acts as a barrier, which encourages the accumulation of phosphoric acid content within the CL while simultaneously inhibiting the leaching of phosphoric acid towards the channel .
 A.Weiß, S.Schindler, S.Galbiati, M.A.Danzer, R.Zeis, Electrochimica Acta 230, 391-398 (2017).
 C.Wannek, I.Konradi, J.Mergel and W.Lehnert, International Journal of Hydrogen Energy, 34, 9479-9485(2009).
 S.Chevalier, M.Fazeli, F.Mack, S.Galbiati, I.Manke, A.Bazylak and R.Zeis, Electrochimica Acta 212,187-194(2016).
Roswitha Zeis received her Ph.D. degree in Physics from the University of Konstanz (Germany) in 2005. She conducted most of her Ph.D. research in the field of organic electronics at Bell Laboratories in Murray Hill, New Jersey (USA). From 2005 to 2008, she stayed in the USA and carried out research on hydrogen fuel cells while holding postdoctoral positions at the Johns Hopkins University, Massachusetts Institute of Technology, and Northeastern University.
In 2009, Dr. Zeis joined Jülich Research Center (Germany) and worked on high-temperature proton exchange membrane fuel cell technologies. Since 2012, she has been the principal investigator of the Helmholtz Young Investigator Group “Investigation of Overpotentials in High-Temperature Proton Exchange Membrane Fuel Cells” at the Karlsruhe Institute of Technology (Germany). Her current research aims to develop and characterize high-temperature proton exchange membrane fuel cells with improved performance and reliability using novel electrolytes, catalysts, and membranes.