A facile approach to improve the electrocatalytic properties of Pt nanoparticles (nm-Pts) has been developed. nm-Pts are deposited on substrate electrode Pt sheet using cyclic voltammetry in sulfuric acid containing H(2)PtCl(6) to get nm-Pt electrode, and then are modified with polypyrrole in an ionic liquid 1-ethylimidazolium trifluoroacetate (PPy-HEImTfa) to obtain the electrode PPy-HEImTfa/nm-Pt. The electrocatalytic performance of PPy-HEImTfa/nm-Pt towards the oxidation of formaldehyde in acidic solution has been studied by cyclic voltammetry and in situ FUR spectroscopy. Results show that PPy-HEImTfa/nm-Pt exhibits high electrocatalytic activity and stability, as compared with nm-Pt electrode or PPy-HEImTfa modified with nm-Pts (nm-Pt/PPy-HEImTfa) under the similar preparation conditions. In situ FTIR spectroscopic measurements confirm that PPy-HEImTfa film on the surface of nm-Pts help to catalyze the oxidation of the adsorbed CO and reduced the poisoning effect of CO on nm-Pt catalyst. (C) 2011 Elsevier B.V. All rights reserved.