Advances in Carbon-Incorporated Non-Noble Transition Metal Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cells

Considerable efforts have been exerted in the development of non-noble metal catalysts (NNMCs) for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). The effects of the preparation strategy, including carbon support, metal and nitrogen precursors, as well as heat-treatment conditions, on the ORR activity for such NNMCs have also been extensively explored. In this review, we mainly focused on the recent advances in carbon-incorporated NNMCs, specifically carbon-incorporated iron nitride (FeCN)-based catalysts. Influences of pyrolysis temperature on the crystalline and local structures, chemical environment, morphology, and ORR activity of FeCN-based catalysts were discussed, and the ORR mechanism was also proposed.