Regulation Strategies on Fe-N-C and Co-N-C Catalysts for Oxygen Reduction Reaction: A Review

Proton exchange membrane fuel cells (PEMFCs) and alkaline membrane fuel cells (AEMFCs) have received great attention as the energy device of next generation. Accelerating oxygen reduction reaction (ORR) kinetics is the key to improve PEMFCs and AEMFCs performance. Platinum-based catalysts are the most widely used catalysts for ORR, but their high price and low abundance limit the commercialization of fuel cell. Non-noble metal-nitrogen-carbon (M-N-C) is considered to be the most likely material to replace Pt-based catalysts, among which Fe-N-C and Co-N-C have been widely studied due to their excellent intrinsic ORR performance and have made great progress in the past decades. With the improvement of synthesis technology and deepening understanding of the ORR mechanism, some reported Fe-N-C and Co-N-C catalysts have shown excellent ORR activity close to that of commercial Pt/C catalysts. Inspired by the progress, regulation strategies on Fe-N-C or Co-N-C catalysts are summarized in this review from 5 aspects: (1) coordinated atoms, (2) environmental heteroatoms and defects, (3) dual-metal active sites, (4) metal-based particle promoter and (5) curved carbon layer. Next, we make our own suggestions on some challenges facing Fe-N-C and Co-N-C research.