In this article we describe further improvement of high-performance Pt monolayer-shell on carbon-supported Pd nanowires/nanorods-core electrocatalysts for the oxygen reduction reaction. This improvement is facilitated by electrochemical deposition of Pd nanostructured cores on functionalized carbon surfaces. We describe in some detail this first electrochemical deposition of Pd nanowires, including the effect of deposition parameters on the deposits morphology, and propose the mechanism of the Pd nanostructures growth. The one-dimensional growth of Pd is ascribed to the hydrogen-underpotential-deposition-mediated layer-by-layer deposition of Pd. The surface structure of deposited nanowires is composed predominantly of the {111}-oriented facets that facilitate the enhanced oxygen reduction and high stability of these electrocatalysts. They have significantly higher Pt mass-, and area-specific activities and performance stability under potential cycling conditions than commercial Pt/C electrocatalysts, which indicates their great potential for resolving the remaining obstacles to commercializing PEMFCs. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.006209jes] All rights reserved.