ELECTROCHEMICAL REDUCTION OF MOLECULAR-OXYGEN ON PLATINUM SINGLE-CRYSTALS

The O2 reduction reaction on Pt (111), (100) and (110) planes is found not to be very sensitive to the structure of the surface in 1 M HCIO4 solution, for which the anion adsorption is weak. On the contrary, the results are orientation and structure-sensitive in 1 M H2SO4, 1 M H3PO4 and 0.1 M HCl+1 M H2SO4: the anion adsorption not only decreases the kinetics of this reaction for a given structure, but also seems to be very structure-sensitive. In sulphuric and phosphoric acid solutions the reaction rate is slower on a Pt (111) plane than on a Pt (110) or on an average Pt (100) plane; in sulphuric acid solutions various treatments, which are known to provide a smaller amount of superficial defects on Pt (100) or (111), induce a slower reaction rate. With Cl- anions, the reaction rate decreases in the order (111) > (110) > (100).