Pt-alloy electrocatalysts -The electrocatalysts were placed in the electrolyte without any potential control (at the OCP) in an oxygen saturated solution and ORR polarization curves were measured immediately after measurement of ohmic resistance and its compensation (under same conditions as in the case of Pt/C benchmark electrocatalyst). The protocol for COelectrooxidation following the ORR measurement was the same as described above. At the end of CO-electrooxidation, 50 cycles of PCA (0.05-1.2 VRHE, 300 mV s -1 , 600 rpm) were performed under the same parameters as in the case of Pt/C benchmark electrocatalyst.