One-step preparation of N-doped graphitic layer-encased cobalt/iron carbide nanoparticles derived from cross-linked polyphthalocyanines as highly active electrocatalysts towards the oxygen reduction reaction
The development of low-cost and structure-controlled precursors has become one of the crucial issues in the improvement of pyrolyzed carbonaceous materials for the oxygen reduction reaction. In this work, a facile and interchangeable cross-linking process has been developed to synthesize polyphthalocyanines with different cross-linking degrees. After the pyrolysis treatment, the cross-linked polyphthalocyanine generated N-doped carbon-encased metal nanoparticle materials. During the pyrolysis treatment, the cross-linked structure of polyphthalocyanine can effectively restrain the aggregation of the metal core and significantly increase the amount of active N species in the pyrolyzed carbon shell. Different from the pyrolyzed pure phthalocyanine, the pyrolyzed cross-linked polyphthalocyanine electrocatalyst shows excellent electroactivity via a 4-electron pathway along with remarkable stability and good methanol tolerance. In addition, the unraveling of the cross-linking degree effect also provides guidance for future design of more efficient non-precious metal catalysts for oxygen reduction and other electrochemical applications.