Polymer Electrolyte Fuel Cells; Ultra-fast X-ray Tomographic Microscopy; Water Management; Low Signal-to-Noise Image Evaluation; Dynamics of Liquid Water in Porous Materials
Xu Hong, Nagashima Shinya, Nguyen Hai P., Kishita Keisuke, Marone Federica, Büchi Felix N., Eller Jens (2021), Temperature dependent water transport mechanism in gas diffusion layers revealed by subsecond operando X-ray tomographic microscopy, in Journal of Power Sources
, 490, 229492-229492.
Bührer Minna, Xu Hong, Eller Jens, Sijbers Jan, Stampanoni Marco, Marone Federica (2020), Unveiling water dynamics in fuel cells from time-resolved tomographic microscopy data, in Scientific Reports
, 10(1), 16388-16388.
Xu Hong, Bührer Minna, Marone Federica, Schmidt Thomas J., Büchi Felix N., Eller Jens (2020), Optimal Image Denoising for In Situ X-ray Tomographic Microscopy of Liquid Water in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells, in Journal of The Electrochemical Society
, 167(10), 104505-104505.
Xu Hong, Marone Federica, Nagashima Shinya, Nguyen Hai, Kishita Keisuke, Büchi Felix N., Eller Jens (2019), (Invited) Exploring Sub-Second and Sub-Micron X-Ray Tomographic Imaging of Liquid Water in PEFC Gas Diffusion Layers, in ECS Transactions
, 92(8), 11-21, The Electrochemical Society, Pennington, NJ 92(8), 11-21.
Bührer Minna, Stampanoni Marco, Rochet Xavier, Büchi Felix, Eller Jens, Marone Federica (2019), High-numerical-aperture macroscope optics for time-resolved experiments, in Journal of Synchrotron Radiation
, 26(4), 1161-1172.
Xu Hong, Bührer Minna, Marone Federica, Schmidt Thomas J., Büchi Felix N, Eller Jens (2017), Fighting the Noise: Towards the Limits of Subsecond X-ray Tomographic Microscopy of PEFC, in ECS Transactions
, Pennington 80(8), 395-402, The Electrochemistry Society, Pennington, NJ 80(8), 395-402.
Hydrogen fed polymer electrolyte fuel cells (PEFC) are expected to play a major role in a future decarbonized energy system, in particular in the mobility sector. Water management is the major limiting factor in PEFC for further increasing power density. Therefore the aim of this project is to improve performance, but also stability and durability of PEFC by unraveling the dynamics of liquid water in the porous gas diffusion layers (GDL) of PEFC. The project will scientifically develop around two PhD theses hosted at PSI in the Electrochemistry Laboratory and the X-ray tomography group (also responsible for the TOMCAT beamline). The project aims at the development of sub-second tomographic imaging of PEFC for visualizing and ultimately understanding the liquid water dynamics in the GDL, which today limits performance. In vehicles and other demanding applications the fuel cell is operated in non-steady state mode, following a transient load profile. This requires a fast characterization technique for understanding of the transient water transport in the GDL. Operando X-ray tomographic imaging (XTM) is a powerful technique able to image the liquid water in PEFCs on the scale of GDL pores with pixel sizes of 2 to 3 micrometers. However, today the fastest operando XTM scans require acquisition times of about 10 s, limiting the technique to investigation of stationary operation conditions and fail to deliver insight into fast snap-off and Haines-jumps dynamics of the liquid phase that are expected to dominate during transient PEFC operation. Further, due to the radiation sensitivity of PEFC, with present imaging conditions only a low number to 3 - 4 tomograms can be acquired without radiation bias, which limits insight, as increased statistics over several cell set-ups are required.The project intends to reduce scanning time by two orders of magnitude vs. state of the art to 0.1s for a 3D-volume. This requires the development of advanced imaging procedures, improving the signal to noise ratio at short scanning times and data post-processing approaches that allow to identify the liquid water phase in the 3D-images from low signal to noise CT data. Further an upgrade of the beamline optics is necessary, where the installation of a new microscope with a high numerical aperture lens (NA of >= 0.35) is planned. With the increased number of scans, the redistribution of the water phase over various timescales will be accessible, enabling an ultimative understanding of the coupling of power limitations at transient PEFC operation with liquid water dynamics at the pore scale level. The new insights will clarify the controversy whether capillary pressure driven liquid flow or root like merging of various independent condensation clusters are the major mechanism of water transport in the GDL. Further the temporal build up of liquid water paths after significant changes of the current density of the cell, understanding of the voltage fluctuations under high humidity operation conditions, as well as the temporary power loss after a fast increase of power density will be understood. Results will provide important input for the GDL structural development allowing for better effective gas phase transport under high current density conditions, enabling higher PEFC power density.