Non-precious metal catalysts as the electrocatalysts for oxygen reduction reaction (ORR) attract great attention due to their activity and stability close to Pt/C. Herein, the iron-based catalysts for ORR are synthesized through the heat treatment of o,m,p-phenylenediamine/iron/carbon precursors. Variation of polymerization, heat-treatment temperature, quantity and source of iron precursors during the synthesis of the catalyst leads to the difference in ORR activity. A relationship between the structure and performance is established through the systematic investigation of synthesis-structure-performance in these catalysts by using advanced characterization methods. It is confirmed that iron, nitrogen, and carbon play different roles in ORR activity, respectively. The formation and amount of Fe-N complex, which are often proposed to be active sites for ORR, are consistent with species and environment of nitrogen and iron. (C) 2015 Elsevier B.V. All rights reserved.