Comparative studies of the electrochemical behaviour of CO2 on a polycrystalline Rh electrode in acid solution by electrochemical and spectroelectrochemical measurements are reported. Aqueous solutions of H2SO4 HClO4 and CF3SO3H have been used. In order to produce r-CO2 adsorbates, different adsorption potentials (E-ad) in the H-atom electrosorption potential range and in the hydrogen evolution region (HER) were chosen. The values of charge density of adsorbate oxidation (q(ox)) depend on Ead, On the solution composition and on the adsorption time (t(ad)) At constant E-ad and t(ad), q(ox) increases in the following order: H2SO4 < CF3SO3H < HClO4 in agreement with the adsorption strength of anions, The same sequence was observed in the oxidation peak potentials of the adsorbates produced. To analyzed the influence of r-CO2 adsorbates in the HER, polarization curves have also been recorded, Studies have been carried out with in situ infrared reflectance spectroscopy. Three techniques were employed: SNIFTIRS, SPAIRS and potential steps, Several main IR bands are observed and associated with CO2 and CO (COB bridge-bonded and COL linearly bonded). Other bands are also observed between 1000-1800 cm(-1) which show the existence of other adsorbed species as well as around 1900-1100 and 2800-3000 cm(-l). This observation leads to the supposition that another more reduced species is formed from CO2,