In this work different imaging parameters and their consequences on the contrast-to-noise ratio (CNR) of water versus void have been studied with an ex-situ XTM experiment at the TOMCAT beamline of the Swiss Light Source (SLS) at Paul Scherrer Institut (PSI). The cathode channels of a double channel XTM cell  have been filled with liquid water, while keeping the anode channels empty, as shown in Figure 1. The CNR(H2O/Void) in the gas channels serves as an indicator for contrast between liquid water and void in the GDL to derive optimized imaging parameters for operando conditions. Over a range of monochromatic beam energies (13.5 – 21 keV) and scan times (0.2 – 10 s) a beam energy of 13.5 keV was found to be mostly appropriate as it provides the highest CNR value. The presentation will focus on the consequences of sub-second XTM acquisition time on the image processing pipeline for the detectability of small water droplets and their connecting paths.
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Figure 1: Quantitative comparison of the contrast-to-noise ratio (CNR) between water and void for different beam energies and scan times (middle); qualitative through-plane slices are given for 0.5 s (left) and 10 s scan time (right).