Pt nanoparticle catalysts supported on carbon black coated with mixtures of Ru and Sn oxides (Pt/Ru-Sn oxide/C) have been screened for their activity and stoichiometry for ethanol oxidation. The compositions, loadings, and properties of the mixed Ru Sn oxide support layers were varied by changing the concentration of base used during their deposition. Cyclic voltammetry at ambient temperature showed that Ru oxide alone provided a significant increase in activity at low potentials over Pt/C, while a small amount of Sn provided a large additional benefit. The most active catalyst had Ru and Sn loadings of 17% and 1.2% by mass, respectively. This was also the most active catalyst for ethanol oxidation at 80 degrees C in proton exchange membrane electrolysis cells, where it provided four times more current than a commercial Pt/C catalyst at 0.25 V vs. a hydrogen evolving cathode. This is comparable to the performance of commercial PtRu/C, and the Pt/Ru-Sn oxide/C catalyst was more selective for the complete oxidation of ethanol to CO2. Thus, in direct ethanol fuel cells, Pt/Ru-Sn oxide/C catalysts would provide greatly increased current and power densities over Pt/C, and improved efficiencies over PtRu/C. (C) The Author(s) 2018. Published by ECS.