N-doped and N/Fe-codoped porous carbon spheres derived from tetrazine-based polypyrrole as efficient electrocatalysts for the oxygen reduction reaction

N-doped and N/Fe-codoped carbon materials are currently recognized as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) because of their high catalytic activity, excellent stability, and superior tolerance to fuel. In this work, a novel kind of tetrazine-based polypyrrole spheres (PTPys) is prepared by protonic acid catalyzed Friedel-Crafts polymerization of bis(N-pyrrolyl)-1,2,4,5-tetrazine (TPy) with dimethoxymethane in dichloroethane. The resultant PTPys with a diameter of 100-300 nm are directly pyrolyzed at 900 degrees C to give N-doped porous carbon spheres (N/Cs-900 electrocatalyst). The N/Fe-codoped porous carbon spheres (Fe/N-Cs-900 electrocatalyst) are then constructed by mixing PTPys with Fe(OAc) 2 followed by pyrolysis at 900 degrees C. The as-synthesized N/Cs-900 and Fe/N-Cs-900 electrocatalysts both have a well-defined spherical architecture together with a relatively high N content, high surface area and porosity. Owing to the synergistic influences, Fe/N-Cs-900 electrocatalyst exhibits excellent ORR activities in both alkaline and acidic electrolytes together with superior poisons tolerance in acidic media, whereas N/Cs-900 electrocatalyst displays ORR activity primarily in alkaline electrolyte. This approach can synthesize heteroatom-doped porous carbon spheres dispensing with the need for any templates, which is of great explored potentiality and utilized value.