Methanol oxidation characteristics of rare earth tungsten bronze electrodes doped with platinum

Rare earth tungsten bronzes, Ln/sub 0.1/WO/sub 3/, and those doped with platinum, PtLn/sub 0.1/WO/sub 3/(Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb), were prepared and their electrocatalysis in methanol electro-oxidation was studied in 1.0M CH/sub 3/OH with 0.5M H/sub 2/SO/sub 4/ at 288-323 K. These electrodes revealed generally a redox behavior due to a WO/sub 3//WO/sup 3-/ couple over 0.15-0.45V (RHE) and realized after doped with Pt a higher specific electrocatalytic activity than that of ordinary Pt electrodes. Pt(5 mole percent (m/o))/Ln/sub 0.1/WO/sub 3/ electrodes exhibited a low rest potential of 0.30-0.39V (RHE) in the methanol solution and current density of the oxidation of 20-60 ..mu..Acm/sup -2/ (true) at 0.60V. Also, the heat of activation (10-13 kcal mol/sup -1/) was much lower than that on ordinary Pt electrodes (20 kcal mol/sup -1/). It was found that the electrocatalytic activity depended upon the lattice constants of bronzes, in a similar manner as the redox potential of WO/sub 3//WO/sup 3+/ couple. Further, the electrodes exhibit a much higher activity towards electro-oxidation of CO or of CH/sub 3/OH in the presence of CO as compared with ordinary Pt electrodes. The results suggested a mediatory action of WO/sub 3//WO/sup 3-/ couple, being effective in oxidative removal of impeding reaction intermediates such as adsorbed CO.