The effect of 1-hexadecyl-3-methylimidazolium trifluoromethanesulfonate (C16MI center dot OTf) ionic liquid (IL) on the catalytic activity of Pt/C or PtMo/C anodes is studied in a proton exchange membrane fuel cell (PEMFC). PtMo nanoparticles (NPs) are synthesized with two different Pt:Mo proportions (13 or 31 at.% Mo) by a borohydride method on the carbon support. The composition, crystalline structure, morphology of the PtMo/C are evaluated by energy-dispersive X-ray spectroscopy, X-ray diffraction and transmission electron microscopy, respectively. The stability tests of the electrocatalysts are carried out in acid medium using cyclic voltammetry measurements. Pt/C or PtMo/C electrocatalysts containing C16MI center dot OTf are assessed in the anode in a H-2/air PEMFC by polarization curve and ac electrochemical impedance spectroscopy. The synthesized PtMo nanoparticles show spherical shape and average particle size of 3.5 nm. The PEMFC performance of PtMo (13 at.% Mo) at anode is very similar than of Pt/C anode. The presence of 15 wt% C16MI center dot OTf in the Pt/C or PtMo/C (13 at.% Mo) anodes let to an increase of the maximum power values, 71 and 107 W g(Pt)(-1) cm(-2), respectively. The catalytic surfaces of nanoparticles are modified due to C-16 MI center dot OTf presence which improved the PEMFC performance. This result agrees with the EIS analysis, where the resistances of charge transfer and mass transfer decrease in the C16MI center dot OTf presence. However, this effect is more pronounced for PtMo/C (13 at.% Mo) catalyst, demonstrate that PtMo/C anodes with a small amount of Mo and C16MI center dot OTf ionic liquid improve significantly the PEMFC performance. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.