Using tin oxide (SnO2) and niobium-doped tin oxide (Nb-SnO2) as alternative electrocatalyst support materials can effectively solve the issue of carbon corrosion in polymer electrolyte fuel cell (PEFC) cathodes. Here, we systematically explore the effect of support surface area, Pt loading, and Pt nanoparticle size on the electrochemistry of these carbon-free electrocatalysts. Reducing the Pt loading leads to an increase in electrochemical surface area, but the specific activity decreases as previously observed in conventional carbon based electrocatalysts. Removing residual chlorine impurities by replacing the H2PtCl6 nanoparticle precursor with Pt(acac) 2 increases the specific activity. Niobium-doping of the SnO2 support also results in an increase in specific activity, due to the increased electronic conductivity. Consequently, the oxygen reduction reaction activity of optimized Pt-decorated Nb-SnO2 is approaching to that of Pt-decorated carbon black, the current state-of-the-art PEFC electrocatalyst. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.