Combined Operando High Resolution SANS and Neutron Imaging Reveals in-Situ Local Water Distribution in an Operating Fuel Cell

• Published in: ACS applied energy materials 2019-12, Vol.2 (12), p.8425-8433
• Main Authors: Martinez, Nicolas, Porcar, Lionel, Escribano, Sylvie, Micoud, Fabrice, Rosini, Sebastien, Tengattini, Alessandro, Atkins, Duncan, Gebel, Gerard, Lyonnard, Sandrine, Morin, Arnaud
• Format: Article
• Language: English
• Subjects: Condensed Matter; Materials Science; Physics
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.9b01266

By producing electricity and heat from hydrogen with high yield and with only water as a byproduct, the proton exchange membrane fuel cell (PEMFC) is one of the most promising carbon-free alternative energy conversion systems for transportation and stationary applications. Water management is a key issue in these systems as it drives performance, thus preventing their large scale implementation. Indeed, numerous studies have shown that a proper water balance should be achieved in operation; that is, water must be present in large quantities in the proton conducting polymeror ionomermembrane, while other components must contain only moderate amounts of it. In this paper, we explore the in situ distribution of water in a working fuel cell using a dual neutron imaging and high resolution small angle neutron scattering approach. We show that by combining these techniques, both liquid water and polymer membrane swelling can be quantified on a micrometer scale, i.e. at the rib-channel level. Cross-analyzed imaging and scattering data revealed the absence of a one-to-one correlation between membrane water content and amount of liquid water accumulated in the flow field. We observed that liquid water tends to accumulate sharply at the channel/rib interface while a smooth hydration pattern was found inside the membrane, reaching a maximum in the middle of the channel. Our results indicate the development of large in-plane and through-plane gradients in relative humidity at millimeter and submillimeter scales, and, consequently, emphasize that the water distribution in the operating fuel cell is governed by complex two-phase flow with evaporation/condensation processes. The in situ multitechniques data sets we have collected at the rib-channel level are direct inputs for flow models needed to unravel and optimize the device function.