STXM pore space visualization relies on filling the pores with a material that STXM can discriminate spectroscopically relative to the other components (carbon support, ionomer, and metal catalyst-Pt) . In these experiments the cathode catalyst decals are embedded with a custom epoxy (TTE, the product of reacting trimethylolpropane triglycidyl ether and 4,4’-methylenebis(2-methylcyclohexylamine in 1:1 wt ratio, which results in a final chemical formula (C10H10N3)n and density of 1.0 g/cm3). While the TTE epoxy is fluid it wets well the electrode inner interfaces filling most of the available space. 100 nm thick microtomed sections of the cathode embedded in TTE are measured by STXM at the C 1s edge at the Canadian Light Source (Saskatoon) or the Advanced Light Source (Berkeley). The C1s stacks, consisting of images at 50-70 energies over 280-330 eV with 100 nm pixels, are converted to optical density, and then fit using standard, quantitative reference spectra (OD1 scale) of carbon-support (Cs), ionomer (I), TTE and Pt components to construct 2D component maps of each component. The grayscale value at each pixel is the nm thickness of that component. The total volume is the sum of Cs, I, TTE, and Pt values at each pixel. The 2D porosity map is then the ratio of the TTE map to the total-volume map, where each pixel has a unit of part per volume (ppvol).
STXM performed using BL 10ID1 at CLS and BL 184.108.40.206 at ALS. Research supported by NSERC.
- S. Shukla, et.al., 231 ECS 2017, Abst 97034, https://ecs.confex.com/ecs/231/webprogram/Paper97034.html
- M.Sabharwal, et al., Fuel Cell, 16 (2016) No.6, 734–753
- H. Ade, et al., Polymers, 49 (2008) 643-675