We present an investigation of the alloying effects of 3d transition metals with palladium, and on their activity towards the oxygen reduction reaction (ORR) in alkaline media, as well as the durability of the electrocatalysts over time. Bimetallic Pd-M (M = Fe, Co and Ni) nanoparticles (NPs) were prepared by an impregnation method followed by reduction under forming gas and a subsequent annealing treatment. In order to enhance the catalytic activity towards the ORR, the bimetallic Pd-M nanoparticles were electrochemically dealloyed. The dealloyed Pd-M nanoparticles had a core-shell structure with a Pd3M-core and a Pd-shell about 1 nm in thickness. The core-shell materials exhibited higher electrocatalytic activity towards the ORR, and longer-term durability when compared to pure Pd. (C) 2018 Elsevier Ltd. All rights reserved.