fig4

Figure 4. (A) CV curves of commercial TKK-Pt/C, MPPNs and PPNWs, recorded at 25 °C in an N₂-purged 0.1 M HClO₄ solution at 50 mV s^-1. (B) ORR polarization curves. (C) Mass activity (MA) Tafel slope and (D) histogram of mass activities at 0.9 V vs. RHE for Pt/C, MPPNs and PPNWs; (E) The ORR polarization curves of MPPNs after the durability test. (F) The mass activities of MPPNs at 0.9 Vvs. RHE.