Preparation of Fe–N–C catalysts with FeNx (x = 1, 3, 4) active sites and comparison of their activities for the oxygen reduction reaction and performances in proton exchange membrane fuel cells

The active sites of Fe–N–C catalysts are nitrogen coordinated iron atoms, FeNx(x = 1–5), that have five possible coordination numbers, corresponding to different ORR activities and PEMFC performances.