Adsorption, oxidation and effect of CO on hydrogen adsorption at smooth rhodium electrodes in acid solution

Abstract

The adsorption of carbon monoxide was studied under steady state conditions on smooth rhodium electrodes in 0.5 M H 2SO 4 at room temperature. The coverage with carbon monoxide is equal to saturation coverage between 0.1 and 0.5 V vs a hydrogen electrode in the same solution. Above 0.5 V it decrease to 0 within 0.2 V. The oxidation of chemisorbed carbon monoxide at constant current is accompanied by the formation of the oxygen layer above 0.6 V. A correction for the contribution of the oxygen layer formation to the anodic charge has to be applied in the determination of the CO ad coverage even at small current densities. The coverage with H ad was determined as a function of potential at constant coverage with preadsorbed carbon monoxide from anodic charging curves. These curves were taken at a sufficiently small current density so that the equilibrium of the Volmer reaction remained practically established. The coverage of CO ad, computed from the charge for the oxidation of CO ad, agreed well with that obtained from the decrease of the length of the hydrogen branch of the charging curves. The isotherms of hydrogen adsorption are of the Temkin type at CO ad coverages above 0.4. The characteristic parameters of the Temkin isotherm were determined as a function of the coverage with CO ad.