Résumé : The interest of self-assembled monolayers (SAM) comes from their wide range of very specific technolog-ical applications. The SAMs having a terminal charged group are of great importance as model surfaces forelectron transfer studies. The electron transfer for highly charged electroactive ions at a SAM modifiedelectrode involves an electrostatic interaction. The present work studies a negatively charged SAM of2-mercaptobenzimidazole-5-sulfonate (MBIS). The adsorption of the molecule on polycrystalline gold isdescribed by X-ray photoelectron spectroscopy (XPS) and the reductive desorption of MBIS. The behaviorof the MBIS monolayer towards the electron transfer of the ferri/ferrocyanide reaction is investigated bycyclic voltammetry and odd random phase multisine electrochemical impedance spectroscopy (ORP-EIS).This technique ensures reliable experiments and enables a statistically founded modeling. The combinedelectrochemical and surface study allows the investigation of the characteristics and electrochemicalproperties of the MBIS monolayer formed on polycrystalline gold to provide a quantitative modeling,which is physically and statistically validated. The major contribution of this work is the use of ORP-EISand XPS to understand how the interaction between a charged SAM and electroactive ions affects theelectron transfer.