Methanol tolerant oxygen reduction catalysts derived from electrochemically pre-treated Bi2Pt2-YIrYO7 pyrochlores

The electrocatalytic activity for oxygen reduction on Bi2Pt2-yIryO7 (y = 0, 0.5, 1, 1.3, 1.4, 1.5, 2) electrodes was examined in 0.5 M H2SO4 in the presence and absence of 0.5 M methanol, using the rotating ring-disk electrode technique. These pyrochlore electrodes exhibited oxygen reduction activity with an onset potential at ca. 0.2 V vs. Hg/ Hg2SO4 only after pre-treatment of potential cycling between -0.6 and 0.6 V vs. Hg/Hg2SO4. This "activation" of the pyrochlores is initiated by a reduction process that produces Bi-0 and Pt-0 at potentials located near the negative limit of the potential cycling range. Depending on the amount of pyrochlore used to fabricate the electrodes and the amount of charge passed during the reductive "activation", a thick layer of a Pt containing material that differs from the pyrochlore structure may be produced. A pre-treatment of potential cycling between -0.3 and 0.8 V vs. Hg/Hg2SO4 did not "activate" the pyrochlores. The oxygen reduction activity and the methanol oxidation activity of the electrochemically treated pyrochlores increased in the order: Bi2Pt0.5Ir1.5O7 < Bi2Pt0.6Ir1.4O7 < Bi2Pt0.7Ir1.3O7 < Bi2PtIrO7 < Bi2Pt1.5Ir0.5O7 < Bi2Pt2O7. Electrochemically treated Bi2Ir2O7 exhibited no catalytic activity.