For the ORR tests, O2 gas was continuously purged to the 0.1 M KOH electrolyte, and the ORR activities of the electrocatalysts were evaluated in an O2-saturated electrolyte via cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements at scan rate of 50 and 5 mV/s, respectively, using a rotation speed of 1600 rpm.