Tötzke, C.; Manke, I.; Lehnert, W.: In Situ Imaging at Large-Scale Facilities. In: Stolten, D. [u.a.] [Eds.] : Fuel cell science and engineering : materials, processes, systems and technology. Vol. 1. Weinheim: Wiley-VCH Verl., 2012. - ISBN 978-3-527-33012-6, p. 493-519
The importance of water management to successful cell operation of polymer electrolyte fuel cells (PEFCs) has directed the focus of extensive research activity on liquid water transport and its effect on cell performance, reliability, and durability of cell components. Water produced from the electrochemical reaction together with water from the humidified inlet gases maintains the hydration level of the membrane which is crucial for high proton conductance. However, excess liquid water can cause flooding of gas diffusion layer (GDL) regions and flow field channels, entailing oxidant starvation and significant power losses. Well-balanced water management is a major challenge to achieve the optimal efficiency and lifetime of these cells [1–7]. In addition to water management, the formation and transport of CO2 bubbles on the anode side in direct methanol fuel cells (DMFCs) has to be understood in order to prevent blockage of anode-side gas channels [8, 9]. In recent years, phosphoric acid-based high-temperature polymer electrolyte fuel cells (HT-PEFCs) have attracted much attention from the fuel-cell community because of the high CO tolerance. Owing to the high operating temperature of 160 ◦C, no liquid water is present in the cells and there is no need to humidify the gases. In order to achieve optimum power densities, the distribution of the electrolyte in the electrodes and the membrane plays a crucial role [10, 11]. In the recent past, imagingmethods have contributed a great deal to the advances in these research fields. Neutron and synchrotron X-ray imaging have become established as indispensable diagnostic tools for the optimization of fuel-cell components, for example, flow field geometry, GDLs or electrode structures, as they are able to reveal water transport processes in operating cells, CO2 bubble formation in DMFCs, or the dynamics of the phosphoric acid distribution in HT-PEFCs in a non-destructive way. In the following, basic principles of these methods and a representative selection of practical applications in fuel-cell research are presented.