A STUDY OF BISMUTH RUTHENATE AS AN ELECTROCATALYST FOR BIFUNCTIONAL AIR ELECTRODES

The electrode kinetics of oxygen reduction and evolution on Ru, Ru/Bi( ad) and Bi2Ru2O7 electrodes were studied in 0.1M KOH. The transport an d current shielding properties of the rotating ring-disk electrode tec hnique were used to obtain the kinetic variables as well as to determi ne the stability of these electrodes. Relatively high catalytic activi ty for O2 reduction was observed on an Ru electrode. The catalytic act ivity of Ru was considerably reduced on the surface modified by ''irre versibly adsorbed'' Bi. The inhibition of O2 reduction was accompanied by a change in the reaction mechanism from a predominately direct ''f our-electron pathway,'' characteristic for O2 reduction on pure Ru, to a significant branching of the reaction to the ''preoxide pathway'' o n the Ru/Bi(ads) electrode. Bi2Ru2O7 exhibited low catalytic activity for O2 reduction and relatively high activity for peroxide decompositi on and/or reduction. Although less active for oxygen evolution than ei ther Ru or Ru/Bi(ad) electrodes, the Bi2Ru2O7 electrode is more stable during O2 evolution than either of these electrodes, with no dissolut ion products detected at the ring electrode.