Identification and Understanding of Active Sites of Non‐Noble Iron‐Nitrogen‐Carbon Catalysts for Oxygen Reduction Electrocatalysis

Abstract

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.

FeN4 Environments upon Reduction: A Computational Analysis of Spin States, Spectroscopic Properties, and Active Species

“…It thus appears that both types of sites might be present in FeNC catalysts, but they may have different catalytic roles. Notably, different preparations yield FeNC catalyst materials with different impurities, side phases, and activities. ,− The preparation conditions might thus play a role in determining which active site motif is dominant, in terms of quantity and catalytic capability.…”

Recent advances in Fe‐N‐C single‐atom site coupled synergistic catalysts for boosting oxygen reduction reaction

“…Of note, recent research directions have revealed how M-N 4 sites' intrinsic activity can be modulated by incorporating heteroatoms, nanoclusters, and nanoparticles into the surrounding environment. [53][54][55] To date, while numerous reviews have summarized the noteworthy advancements in M-N-C SACs in lieu of precious metal-based electrocatalysts, 56,57 the systematic progress and the impact of associated particles on SACs ORR activity have been relatively scantily documented. 31,58 Therefore, this review exclusively focuses on the regulation in Fe-N 4 site surroundings within the Fe-N-C SACs, in view of establishing the structureactivity relationship that can influence the intrinsic activity (Figure 1C).…”

Local Oxidation Induced Amorphization of 1.5‐nm‐Thick Pt–Ru Nanowires Enables Superactive and CO‐Tolerant Hydrogen Oxidation in Alkaline Media

“…Under alkaline conditions, the cathode oxygen reduction reaction (ORR) are kinetically accelerated on a richer variety of catalysts that can be composed by nonprecious elements, and endowed with improved stabilities compared to the acid scenarios. [7][8][9][10] However, the anode hydrogen oxidation reaction (HOR) is severely repressed in alkaline conditions even by the state-ofthe-art Pt and/or its derived electrocatalysts, presenting ≈2 orders of magnitude lower activities than that in acidic media. [11] More fatally, these catalysts tend to be poisoned by trace CO in H 2 supply and deactivate rapidly.…”