The heterogeneous rate constant for the anodic oxidation of Mn(II) at PbO2-based mixed oxide electrodes in 1.0M HC104 was determined as a function of high doping levels by the oxides of Group IIIA and VA metals. Electrodes were prepared by electrodeposition from solutions containing Pb -~+ and the doping metal ions in 1.0M HC104. Doping with the Group IIIA metal oxides results in a slight decrease in the rate constant for Mn 2+ oxidation; however, doping with the Group VA metal oxides results in significant electrocatalysis of the anodic oxygen transfer reaction, as compared to a pure ~-PbO2 electrode. The rate constant at the mixed oxide deposited from a solution of 1.0 mM Bi~+/1.0 mM Pb 2+ was at least 25 times greater than for pure ~-PbO2, becoming virtually mass-transfer limited at the mixed oxide electrode to rotation rates of 3600 rev min-'. (mA -I ) 1.5 D m J J ~J f

X‐ray structural data, O2 evolution overpotentials false(ηO2↑false) , and rate constants false(kfalse) are compared for anodic oxidation of Mn(II) false(n=5 eq mol−1false) and 2‐thiophene carboxylic acid (2‐TCA) at Bi‐doped PbO2 in 1.0M HClO4 . It is concluded that the rutile structure of pure β‐PbO2 deposited anodically from 1.0M HClO4 containing Pb(II) is retained even as the Bi(III) content is increased to normalBi/normalPb≥normalca.0.7 , i.e., mole fraction normalBi=0.4 . There is no evidence of a new oxide phase being formed. Crystallites of the normalBi‐PbO2 are deposited with an increasing preferential orientation of the 020‐plane parallel to the Au substrate surface as the ratio Bi/Pb is increased. Increasing values of k and decreasing values of ηO2↑ appear to be correlated with the increased preferential orientation. However, change in preferential orientation is concluded not to be the primary determining factor in the electrocatalytic phenomena. The kinetic results are discussed also on the basis of the so‐called “volcano plot” of ηO2↑ as a function of the enthalpy of transition false(normalΔHnormalt0false) between the two highest oxide phases for metal oxide electrodes.

The formation and stripping of palladium oxides on a palladium electrode in a 0.1M normalLiOH solution was studied by cyclic voltammetry. Cyclic polarization methods were used to form palladium oxides on the surface of the palladium electrode. Three different types of palladium oxides were found to be formed in alkaline solutions. A higher oxidation state of palladium oxide false(PdO3false) can be formed (induced) on the surface of the electrode even at low anodic potential limit, 0.6 V (vs. SCE). Strong evidence that PdO3 can only be formed in a specific potential range is presented. From the voltammograms obtained after a long cyclic polarization time, the peak in the range of −0.47 to −0.60 V could be attributed to the reduction of dehydrated normalPdO .