Pinhole on-line Electrochemical Mass Spectrometry (POEMS) system was constructed by using a pinhole below ten micron covered with a Teflon film as gas inlet. The 20 wt% electrocatalysts with different molar ratio for platinum and iridium were synthesized by a modified polyol method. These catalysts were physically characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. The electrocatalytic activity and reaction intermediates of Pt/C and Pt-Ir/C electrocatalysts for the ethanol oxidation reaction (EOR) were investigated by potentiodynamic and potentiostatic techniques with ODEMS system. Faster kinetics for CO stripping on Pt-Ir bimetallic alloys can be deduced that a ligand effect of Ir is operated on the Pt electronic structure. The potentiodynamic and potentiostatic tests for ethanol oxidation show that, although kinetics of the reaction is faster on Pt/C, Pt-Ir/C electrocatalysts exhibit higher ethanol oxidation efficiency. The average CO2 current efficiency (CCE) was also determined on both electrocatalysts after calibration of the m/z = 44 signal: the CCE value can reach up to 15% on Pt-Ir/C at room temperature, compared to ca. 7% on Pt/C, which proves the powerful ability of Ir for the C-C bond breaking. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.