Electrochemical deposition and dissolution of Fe species for N-doped carbon to understand the degradation mechanism of Pt-free oxygen reduction catalysts

The enhancement in oxygen reduction reaction (ORR) activity is achieved by the introduction of Fe species via the Fe electrochemical deposition-dissolution treatment into a metal-free nitrogen-doped carbon (P-PI) catalyst, which is prepared by the pyrolysis of polyimide fine particles. The thus-obtained Fe-containing P-PI catalyst suffers activity decay during the durability test, evidenced by the negative shift of half-wave potential, the decrease in limiting current density, the number of electrons transferred, and the ratio of the rate constant for 4-electron ORR to that for 2-electron process, and the increase in H2O2 production percentage. The decayed ORR activity can be recovered by another Fe electrochemical deposition-dissolution treatment, demonstrating the predominant role of Fe leaching in activity degradation as well as the effectiveness of the electrochemical treatment in activity restoration.