Rh modified Au(111-25 nm) film electrodes prepared by electron beam evaporation and galvanostatic deposition were employed to study adsorption and electro-oxidation of formic acid (HCOOH) in 0.1 M sulfuric acid solution using in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). When HCOOH was introduced at the hydrogen adsorption potential range, CO was formed and adsorbed in atop (COL) and bridge (COB) configurations, co-adsorbing with water molecules. Formation of formate together with COL and COB was detected when HCOOH was introduced at 030 V, while only formate was observed at 0.55 V. The HCOOH oxidation on Rh film electrode in acidic media is significantly affected by the surface oxides and adsorbed CO and proceeds, not excluding a possible direct oxidation of HCOOH to CO2, via two indirect oxidation pathways involving dissociative adsorption of HCOOH with the formation of main reactive intermediate formate and mostly blocking CO intermediate. (C) 2016 Elsevier B.V. All rights reserved.