Bimetallic alloys based on Pt and Y are potential cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high oxygen reduction reaction (ORR) activity. Nevertheless, the synthesis of carbon supported Pt-x Y catalysts is challenging due to the low standard reduction potential of yttrium compared to platinum. Hence, extended electrochemical testing in actual PEMFCs remains elusive, especially with respect to catalyst degradation upon voltage-cycling. In this publication, we present the synthesis of a bimetallic Pt-x Y/C catalyst via impregnation of commercial Pt/C with an yttrium halide precursor and subsequent heat-treatment in H-2 at 1200 degrees C. This catalyst showed a high specific ORR activity, at a mass activity similar to Pt/C due to its comparably low electrochemical surface area (ECSA). On the other hand, the large particle size of the here synthesized Pt-x Y/C catalyst (approximate to 10 nm) resulted in a significantly enhanced stability versus degradation in an accelerated stress test (AST) based on voltage-cycling between 0.6 and 1.0 V-RHE at 50 mV s(-1), showing a superior ECSA, ORR activity and H-2/air performance after 30000 cycles compared to a standard Pt/C catalyst. (C) The Author(s) 2018. Published by ECS.