As presented in our previous work [5,18], the SEM and TEM images of both front (0 ) and back (180 ) for these carbon-supported Pt catalysts provide information about the location of Pt particles; the exterior Pt particles are defined by the SEM images, whereas the interior Pt particles are defined by the Pt particles in the TEM images that had not been observed with SEM, so that all of the Pt particles were accounted for.