Comparative EQCM study on electrooxidation of carbon oxides adsorption products on noble metals and their alloys. Polycrystalline Pd-based systems

CO2 reduction and CO adsorption on Pd alloys with Pt and Rh (Pd–Pt, Pd–Rh, Pd–Pt–Rh) have been studied by cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The values of surface coverage, eps (electron per site) and potential of the oxidation of CO2/CO adsorption products depend on alloy surface composition. The oxidation of reduced CO2 on Pd-poor Pd–Pt–Rh alloys proceeds more easily (at lower potentials) than on Pt or Rh. On the other hand, in the case of Pd–Pt and Pd–Rh alloys the adsorbate oxidation is more difficult and requires higher potentials than on pure metals. The EQCM response in CO2/CO adsorption experiments is affected not only by the effects connected with the changes in mass attached to the resonator but also by the non-mass effects including changes in metal–solution interactions and variation of solution density and viscosity in the vicinity of the electrode. The comparison of adsorption parameters suggests that the products of CO2 reduction and CO adsorption on Pd alloys are not identical.