High loading of single atomic iron sites in Fe–NC oxygen reduction catalysts for proton exchange membrane fuel cells

Abstract

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Molecular Catalyst Synthesis Strategies to Prepare Atomically Dispersed Fe-N-C Heterogeneous Catalysts

“…These putative ZnNx sites 21 prevent access to Nx sites by FeCl2 and formation of additional FeNx sites under the low-temperature metalation conditions. Previous reports have demonstrated replacement of Fe by Zn during high-temperature heat treatment (750-1000 °C) [21][22][23] The molecular precedents noted in Figure 1B-ii raised the possibility of an alternative transmetalation strategy, in which acid-promoted removal of the Zn ions could be followed by low-temperature metalation.…”

“…Taken together, the data indicate that the lowtemperature, solution-phase metalation conditions directly generate FeNx sites, without requiring a subsequent hightemperature pyrolysis step. 22,23 Some portion of the Zn originating from the MOF precursor remains in this material (1.2 wt% Zn, Table S2, Supporting Information) and represents a fraction of the atomically dispersed species observed by AC-STEM (Figure 2D). These putative ZnNx sites 21 prevent access to Nx sites by FeCl2 and formation of additional FeNx sites under the low-temperature metalation conditions.…”

“…20 Recent efforts have identified new multi-step routes to Fe-N-C materials with improved Fe dispersion and site density. [21][22][23][24] These advances are complemented by studies implicating FeN4 or related mononuclear FeNx sites as the source of catalytic reactivity. 25 -27 The long-recognized analogy between these FeNx sites and the tetragonal N4 metal binding site in Feporphyrins and related Fe-macrocycles, 25,28,29 prompted us to consider whether metalation strategies commonly used for the preparation of macrocyclic metal complexes could be adapted to prepare Fe-N-C materials.…”

Synthetic carbon nanomaterials for electrochemical energy conversion

“…In order to replace the Pt catalyst for commercial applications in proton-exchange membrane (PEM) fuel cells, the ORR activity of an electrocatalyst under acidic conditions is the most important criterion. 141,142 In 2017, an atomic Fe-doped carbon (Fe-NC) was fabricated through the pyrolysis of ZnFebased MOFs with a controlled particle size from 20 nm to 1 µm. 143 The isolated Fe atoms were clearly observed in the carbon matrix in HAADF-STEM images.…”

Atomically dispersed Co in a cross-channel hierarchical carbon-based electrocatalyst for high-performance oxygen reduction in Zn–air batteries

“…[9][10][11][12][13] Among them, the atomic Co-N 4 site has been reported to be one of the most effective catalytic active sites for the ORR. Therefore, maximizing the density of atomic sites [14][15][16] and optimizing the hierarchical pore channels of the carrier [17][18][19] are crucial to improve the catalytic efficiency. Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials formed by metal atoms and organic ligands through coordination interactions, and have become one of the most outstanding precursors for M-N-C based ORR SACs due to their unique structural and compositional characteristics.…”