Facile synthesis of Fe3C-dominated Fe/Fe3C/FeN0.0324 multiphase nanocrystals embedded in nitrogen-modified graphitized carbon as efficient pH-universal catalyst for oxygen reduction reaction and zinc-air battery

•A facile strategy is developed to synthesize multiphase Fe-based catalyst.•The Fe/Fe3C/FeN0.0324@N-GC exhibits excellent pH-universal ORR activity.•It possesses better battery performance than Pt/C in alkaline and neutral media.•The activity is attributed to the synergy among Fe-based sites dominated by Fe3C.•The active of Fe-based sites is probed by DFT calculation: Fe3C > Fe > FeN0.0324.