Electrochemical processes at positively polarized Mo2C derived carbon (C(Mo2C)) electrical double layer capacitor (EDLC) electrode in 1-Ethyl-3-Methylimidazolium tetrafluoroborate ionic liquid at different cell potentials have been studied using in situ synchrotron radiation excited X-ray photoelectron spectroscopy (in-situ XPS) method. Symmetric two-electrode cells were studied using in situ XPS method within very wide cell potential region up to 4.0 V. At cell potentials higher than 2.6 V the cross-over of the limit of the ideal polarizability of the capacitor electrodes has been observed and different faradaic processes have been verified by the cyclic voltammetry and in situ XPS methods. Thus, the supercapacitor cell potential vs. in-situ XPS signal relationship have been analysed identifying the possible electrochemical reactions taking place at the positively polarized working electrode vertical bar ionic liquid interface at the extreme EDLC cell potentials applied. (C) 2014 The Electrochemical Society. All rights reserved.