Pt supported on carbon black, commonly used as PEM fuel cell catalyst, underlies electrochemical instabilities in terms of carbon corrosion and platinum degradation. To better understand the influence of the support on nature and extent of catalyst aging, Pt was synthesized on four different substrates: Carbon black, multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO) and a nanocomposite of indium tin oxide with rGO (ITO-rGO). The four Pt catalysts and the separate supports were studied on their durability using an accelerated stress test (AST, -0.02-1.40 V-SHE). Comparable platinum degradation was shown by losses of electrochemically active surface area (EASA) and activity for oxygen reduction reaction (ORR) and by identical location transmission electron microscopy (IL-TEM). With respect to the supports, highest instability of carbon black was observed investigating the double layer capacitance and amounts of hydroquinone (HQ) species. MWCNTs showed the lowest degradation. Thus, AST provoked strongly different extents of support aging but similar Pt degradation. In view of complex FC catalyst degradation mechanism, only negligible Pt detachment caused by support degradation and rather dominating Pt dissolution and agglomeration-additionally evidenced by IL-TEM-is assumed here. Regarding ITO-rGO, neither carbon support nor platinum stabilization by ITO nanoparticles has been observed. (C) The Author(s) 2017. Published by ECS.