The first stage of the two-stage ion-beam processing is the formation of flat and smooth cross-section by a broad ion beam. The second stage is the selective removal of the ionomer in the catalyst layer by a focused ion beam. Scanning ion microscopic (SIM) images were obtained after the first and second stage. Smoothing filter was applied on the obtained SIM images. The SIM image after the second stage was then conducted threshold by Otsu method and a carbon distribution map was obtained. A pores distribution map is obtained from a combined image of the SIM image after the first stage and the carbon distribution map. The threshold was determined by a p-tile method with ionomer to carbon ratio (I/C). Ionomer distribution was extracted from the carbon and pores distribution maps.
The ionomer distribution of the catalyst layer with I/C 2.0 was analyzed as shown in Figure 1. A catalyst coated membrane was fabricated by a doctor-blading and decal-transfer method . Lower side in the figures is the interface with a polymer electrolyte membrane (PEM) and upper edge is the bottom in the fabrication process before decal-transferring. The through-plane ionomer distribution is not uniform. Thin ionomer layer was formed at the interface with the PEM. This can be because of deposition of ionomer during the drying process.
This work was supported by JSPS KAKENHI Grant Number 15H03932.
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