A SnCl2 shell on Pt metal core nanoparticle synthesis technique has recently been demonstrated to permit electrostatic layer-by-layer (LbL) assembly of well-ordered electrocatalysts without precipitation onto porous carbon supports. In this paper, the electrocatalytic activity of the LbL-assembled Pt nanoparticles is shown to depend critically upon removal of surface-adsorbed Sn (Sn-ads). By subjecting the synthesized Pt nanoparticle electrodes to potential sweeps greater than 1.0 V vs reversible hydrogen electrode, Sn-ads are removed and a nearly threefold enhancement in oxygen reduction reaction (ORR) specific activity over commercial catalysts is obtained. In contrast to this electrochemical acceleration approach, we also investigate electroless, wet-acceleration methods for Sn-ads removal. Energy-dispersive spectroscopy and inductively coupled plasma-mass spectrometry are used to quantify the Pt/Sn ratio in the electrode assemblies as a function of immersion time in solution (both alkaline and acidic) and during electrochemical acceleration, respectively. Charging current for the underpotential deposition of protons on the Pt nanoparticle surface is used to monitor the removal of Sn-ads during electrochemical acceleration, followed by ORR activity measurement in saturated perchloric acid (HClO4). Wet-chemical acceleration in NaOH solution is found to remove similar amounts of Sn as compared to the electrochemical technique. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3454729] All rights reserved.