Non-noble iron-nitrogen-carbon (Fe-N-C) catalysts have been explored as one type of the most promising alternatives of precious platinum (Pt) in catalyzing the oxygen reduction reaction (ORR). However, their catalytic ORR activity and stability still cannot meet the requirement of practical applications. Active sites in such catalysts are the key factors determining the catalytic performance. This review gives a critical overview on identification and understanding of active sties of non-pyrolytic and pyrolytic Fe-N-C catalysts in terms of design strategies, synthesis, characterization, functional mechanisms and performance validation. The diversity and complexity of active sites that greatly dominate the progress of Fe-N-C catalysts include Fe-containing sites (Fe-based nanoparticles and single-atom Fe-species) and metalfree sites (heteroatoms doping and defects). Meanwhile, synergistic effects are also discussed in this review with emphasis on the interaction among multiple active sites. Although substantial endeavors have been devoted to develop the efficient Fe-N-C catalysts, some challenges still remain. To facilitate further research on Fe-N-C catalysts toward practical applications, some research perspectives are prospected in the aspects of innovative synthesis methods, active-sites modulation strategies, high-resolution ex situ/in situ/ operando characterization techniques, theoretical calculations, and so on. This review may provide a guideline for identifying and understanding activesites for developing high-performance Fe-N-C catalysts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.