N-doped carbon prepared by pyrolysis of dicyandiamide with various MeCl2·xH2O (Me = Co, Fe, and Ni) composites: Effect of type and amount of metal seed on oxygen reduction reactions

N-doped carbon was prepared from dicyandiamide as the source for both carbon and nitrogen. Dicyandiamide was pyrolyzed at 900 °C on various metal chlorides (MeCl2·xH2O, Me = Co, Fe, and Ni) to clarify the effects of metal type on the properties of the N-doped carbon. The results showed that electrochemical and physical characteristics of the N-doped carbon were altered by the type of metal seed. The N-doped carbon from Co showed the best performance in oxygen reduction reactions (ORRs) and the order of ORR activity was N-doped carbon from Co > Fe > Ni. Raman and XPS studies revealed that the metal type during pyrolysis step determined degree of sp2-carbon network, and ORR activity of N-doped carbon was improved as the degree of sp2-carbon network increased. The effects of the amount of metal precursor on activity of ORRs and rate of H2O2 formation were faint but the carbonization yield of dicyandiamide increased as the amount of metal precursor increased. The catalysts optimized by altering the type and amount of metal seed showed a 0.60 V (vs. Ag/AgCl) onset potential and a 42% oxygen reduction reactivity at 0.40 V (vs. Ag/AgCl) compared to that of a commercial Pt/C catalyst.

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► N-doped carbon was prepared as a catalyst towards oxygen reduction reaction.
► Co, Fe, and Ni chlorides were used as seeds for carbonization of dicyandiamide.
► The type of seed metal alters the degree of sp2-bonding of carbon.
► Increasing degree of sp2-bonding of carbon improves catalytic activity.
► Amount of seed precursor does not significantly affect the ORR activity.