Electrochemical characterization of the surface and methanol electrooxidation on Pt–Rh–Pd ternary alloys

Methanol adsorption and electrooxidation have been studied on Pt–Rh–Pd alloys using cyclic voltammetry and chronoamperometry. Pt–Rh–Pd electrodes were prepared by a potentiostatic electrodeposition on a gold wire from chloride solutions. Alloy bulk composition was determined by SEM/EDAX measurements. Alloy surface composition was estimated adapting Rand and Woods's method for homogenous binary noble metal alloys utilizing the potential of surface oxide reduction peak. Electrode real surface area was calculated from the charge due to surface oxide formation/reduction. Methanol was oxidized both in stripping voltammetric experiments and continuously under potentiostatic conditions from 1 M CH3OH/0.5 M H2SO4 solution. The values of electron per site, surface coverage and oxidation potential were used for the characterization of methanol adsorption products. The comparison of these results with analogous data for CO2 and CO adsorption has revealed high similarity between CO2 and methanol adsorption products, both consisting of mainly linearly and bridge-bonded CO species, however, with a higher contribution from bridge-bonded CO in the case of methanol. Current densities obtained during continuous methanol oxidation were the highest for Pt–Rh–Pd alloys with initial bulk composition 30.6% Pt, 23.7% Rh, 45.7% Pd, being of the same order as for pure Pt electrode.

Research highlights▶ Pt–Rh–Pd activity in methanol adsorption/oxidation depends on surface composition. ▶ Pt–Rh–Pd real surface area/composition can be estimated by cyclic voltammetry. ▶ Methanol adsorbate structure is more similar to adsorbed CO2 rather than CO. ▶ High surface rhodium content contributes in low methanol dehydrogenation rate.