Operando Sub-Second Tomographic Imaging of Water in PEFC Gas Diffusion Layers

X-ray tomographic microscopy (XTM) of liquid water in polymer electrolyte fuel cells (PEFC) has proven a valuable tool in order to improve understanding of water transport in the gas diffusion layer (GDL) [1-5]. So far, in-operando X-ray tomographic microscopy was restricted to constant operation conditions since the minimal XTM scan time of a few seconds [4] was not sufficient to capture the dynamics of the water distribution under transient operation.

The presentation reports about the developments to reduce the scan time of in-operando XTM below a second at the TOMCAT beamline of the Swiss Light Source. First of all, this offers the possibility to study the evolution of the liquid water distribution in the GDL during transient PEFC operation conditions. Second, the shorter scan times reduce the X-ray dose to the cell and increase the number of XTM scans before radiation induced degradation biases the cell electrochemistry and consequently the water distribution [6].

The consequences of the reduced exposure time and lower number of angular steps on image quality are discussed and the temporal and spatial development of the water distribution in the channel and the GDL following a current density variation from 0.1 A/cm² to 1.0 A/cm² (see Figure 1) will be presented. Special focus will be put on channel vs. land variations, percolation paths of the liquid water and their stability over time.

References

[1] A. Schneider, et al., J. Power Sources, vol. 195 (2010), pp. 6349-6355.

[2] P. Krüger, et al., J. Power Sources, vol. 196 (2011), pp. 5250-5255.

[3] J. Eller, et al., J. Electrochem. Soc., vol. 158 (2011), pp. B963-B970

[4] J. Eller, et al., ECS Trans., vol. 41 (2011), pp. 387-394.

[5] T. Rosén, et al., J. Electrochem. Soc., vol. 159 (2012), pp. F536-F544.

[6] J. Eller, et al., J. Power Sources, vol. 245 (2014), pp. 796-800.

Figure 1: Left: XTM through-plane slice of a single channel cell about 60s after current jump from 0.1 to 1 A/cm². Cathode flow field is on top and identified liquid water is highlighted in blue. Right: 3D rendering of the water in the cathode. The flow field is removed for visualization of the water accumulation under the ribs.