Abstract
Polymer electrolyte fuel cells (PEFC) require a sophisticated water management to operate efficiently, especially at high current densities which are needed to reach system cost targets. The description of the complicated two-phase water transport remains a challenge in PEFC models and requires experimental validation on various length scales. In this work, operando X-ray tomographic microscopy (XTM) with scan times of 10 s was used to depict the liquid water at defined conditions at a technically relevant cell temperature of 80°C. Cells with Toray TGP-H-060 gas diffusion layer (GDL) with microporous layer (MPL) and different rib width were operated with different feed gas humidifications (under- and oversaturated) and current densities between 0.75 to 3.0 A/cm2. Based on the quantification of the local and average saturation, the distribution of water cluster size is analyzed. Different categories of the water cluster connectivity are defined and quantified. The analysis is complemented with numerical simulations of the permeability in the liquid phase of the GDL that is correlated to saturation for the different GDL domains. The numerical simulations of the pressure drop of liquid water flow from the catalyst layer toward the gas channels in channel-rib repetition units allows for conclusions on cluster growth mechanisms.
Highlights
During operation with H2/O2 the saturation increased with current density, reaching average values of up to 52% under the rib at 3.0 A/cm[2] and 78% rH feed gas humidity
Efforts to process XTM data with lower signal to noise characteristics that is required to decrease the scan times are ongoing[55]
Summary
In order to provide the required operating conditions with dew points of the reactants around 80◦C, the set-up was equipped with in-house designed heated gas tubes which allow the cell to turn with exerting only a minimal torque, to allow for undisturbed imaging. Imaging.—Operando XTM scans in absorption contrast mode were performed at the TOMCAT beamline of the Swiss Light Source (SLS)[36] using a fast, CMOS technology based camera (pco.Dimax, Germany), that allows even ultra fast sub-second XTM scans.[37] The pco.Dimax camera was mounted on a microscope (ELYA solutions, Czech Republic) equipped with a continuous zoom objective providing magnification ranging from 2× to 3.9× This combination provides a pixel size of 2.9 × 2.9 μm[2], about 5.8 × 5.8 mm[2] field of view and 2.44 × 10−17 m3 voxel size (2.44 × 10−2 pL) at the highest magnification and full chip readout (2016 × 2016 pixels). For calculating the pressure drop within the liquid phase, a flow rate boundary condition of 5.76 × 10−6 l/(min cm2) per 1 A/cm[2] was applied for liquid water at 80◦C (density of 971.8 kg/m3, viscosity of 3.9 × 10−4 kg/ms)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
