The adsorption of carbon oxides on a palladium electrode from acidic solution

Abstract

The adsorption of carbon oxides from sulfuric acid solution on a palladium electrode was investigated with electrochemical and radiometric methods. It was found that adsorption of CO takes place in the 0.0–0.8 V range. During the CO adsorption the anodic (below 0.15 V vs. SHE) and cathodic (above 0. 15 V vs. SHE) currents are passing through the solution | electrode interface. Mechanisms for the CO adsorption and the final product structure have been proposed. A small amount of adsorbed CO 2 on the surface of the palladium electrode has been observed. A strong correlation between the decrease in the real surface of the palladium electrode and the currents of sorbed hydrogen during its oxidation has been found. 1. Carbon monoxide adsorption on palladium electrode from acidic solution (0.5 M H 2SO 4) occurs at the potentials below 0.9 V (vs. SHE) 2. The main products of CO adsorption on Pd at potentials where no hydrogen absorption occurs are CO species that seem to be mostly bridge bonded to Pd, also a more reduced form of CO adsorption product should exist on the Pd surface. A certain amount of CO species linearly bound is also possible [13–21] 3. The CO adsorption products at potentials where hydrogen absorption occurs, reflect experimental conditions strongly. Probably they are in a more reduced form in comparison with the adsorption products at more positive potentials 4. A decrease of the real palladium surface during CO adsorption and cyclic electrode polarization is observed. 5. Strong correlation between the decrease of the real surface of the palladium electrode and the currents for the sorbed hydrogen oxidation has been found. One of the oxidation peaks related to the sorbed hydrogen oxidation (the smaller at positive potentials) probably corresponds to the oxidation of adsorbed hydrogen. 6. A small amount (almost negligible) of carbon dioxide is adsorbed on the palladium electrode.