This work presents carbon supported Platinum (Pt) nanoparticles decorated with a submonolayer of Bismuth (Bi) to enhance the anodic electro-oxidation efficiency fora Direct Formic Acid Fuel Cell (DFAFC). The coverage of Bi adatoms, as measured by cyclic voltammetry was controlled in the range of 15-75%. This ex situ study of the Bi decorated Pt/C catalysts was done using a three electrode electrochemical cell at room temperature to access formic acid electro-oxidation performance and durability. Two commercial Pt/C catalysts were investigated of varying average size: 2.4 nm and 3.4 nm. An optimal Bi coverage was observed to be 54% coverage or greater for both catalyst sizes, resulting in a favorable decrease in the formic acid onset potential by greater than 0.1 V. The 3.4 nm catalyst demonstrated higher performance over that of 2.4 nm, with a 23-fold current density increase at 0.2V vs. RHE. The results indicate that Bi decorated Pt nanoparticles have excellent electrochemical properties for the electro-oxidation of formic acid (high electro-catalytic activity and excellent stability) due to a combination of the electronic effect and third-body effect, thereby promoting the non-poisoning direct electro-oxidation reaction pathway. Based on position of CO stripping peak for 15% Bi coverage, Pt-COads bond strength decreased for 3.4nm Pt/C whereas no shift was observed in the Pt-COads bond strength for 2.4 nm Pt/C. Chronoamperometry results show much better long-term electro-catalytic activity for Bi decorated Pt nanoparticles. (C) 2013 Elsevier Ltd. All rights reserved.