The surface of the Kapton film appears slightly dark after
being peeled off from the catalyst layer, as shown in Fig. 2. In
order to identify the dark material, small pieces were cut from
the middle of the substrate sheets (both anode and cathode)
that experienced hot-pressing at pressures of 1.0 and 4.0 MPa,
and then were subjected to EDX analysis. No Pt or PtRu peaks
are found in the EDX spectra of any of the four samples, as
shown in Fig. 3. For every sample, three peaks appear in the
EDX spectrum corresponding to C, N and O species of th