Electrocatalytic performance in oxygen reduction reaction. (a) LSV curves of (dashed curves) Pt-NC, (solid curves) PtCo-NC, and (black curve) commercial Pt/C in 0.1 M HClO4, and the corresponding (b) charge transfer number and (c) Tafel plots. In (c), the star marks the DOE 2020 target. (d) Mass activity of the samples and 20% Pt/C at +0.85 V vs. RHE. The blue and yellow columns represent the Pt-NC and PtCo-NC samples, respectively.