Coexisting Single‐Atomic Fe and Ni Sites on Hierarchically Ordered Porous Carbon as a Highly Efficient ORR Electrocatalyst

Abstract

Among them, the nitrogen-coordinated transition-metal (TM) single-atoms (SAs) supported on carbon substrates have emerged as a new class of ORR electrocatalysts with enormous potentials. [3-5] These SA electrocatalysts (SAECs) anchor TM-SAs to the carbon substrates via TMnitrogen (TMN x) coordination bonds that also act as the ORR active sites. It has been commonly accepted that the ORR activity of such TMN x-coordinated SA sites can be promoted by optimizing the binding strengths of ORR intermediates (e.g., *O 2 , *OOH, *OH, *O) to the active site via the altering of their electronic structures. [6] Various approaches have been reported to alter the electronic structures of TMN x-coordinated SA sites by modulating N types and coordinating numbers, [7] partially replacing N with other nonmetal elements (e.g., O, S, and P), [8] or the chemical compositions of carbon substrates. [9] Recently, the hetero-SAs (h-SAs) involving two different TMs (e.g., Co/Zn, Fe/Co, Fe/ Zn) have been successfully anchored to the carbon substrates as ORR SAECs. [10] Such an approach takes the advantage of the coexistence of two different TM-SA sites, through the pairing The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials is critically important for sustainable large-scale applications of fuel cells and metal-air batteries. Herein, a hetero-single-atom (h-SA) ORR electrocatalyst is presented, which has atomically dispersed Fe and Ni coanchored to a microsized nitrogen-doped graphitic carbon support with unique trimodal-porous structure configured by highly ordered macropores interconnected through mesopores. Extended X-ray absorption fine structure spectra confirm that Fe-and Ni-SAs are affixed to the carbon support via FeN 4 and NiN 4 coordination bonds. The resultant Fe/Ni h-SA electrocatalyst exhibits an outstanding ORR activity, outperforming SA electrocatalysts with only Fe-or Ni-SAs, and the benchmark Pt/C. The obtained experimental results indicate that the achieved outstanding ORR performance results from the synergetic enhancement induced by the coexisting FeN 4 and NiN 4 sites, and the superior mass-transfer capability promoted by the trimodal-porous-structured carbon support. The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials to replace the scarce platinum-group-metal-based ones is critically important for sustainable large-scale commercial applications of fuel cells and metal-air batteries. [1] The extensive research efforts over the recent years have led to a variety of The ORCID identification number(s) for the author(s) of this article can be found under

Sulfate Ions Induced Concave Porous S‐N Co‐Doped Carbon Confined FeCx Nanoclusters with Fe‐N4 Sites for Efficient Oxygen Reduction in Alkaline and Acid Media

“…[20,21] Polystyrene spheres and silica are commonly used as templates for making pores. [22][23][24] For example, Shui et al coated ZIF-8 with mesoporous SiO 2 , not only obtained more mesopores, but also successfully prepared a concave Fe-N-C catalyst with high density active sites. [25] However, the inconvenient point is that both polystyrene spheres and silica require additional removal steps.…”

Operando XAS/SAXS: Guiding Design of Single‐Atom and Subnanocluster Catalysts

“…The charge transfer from Ni atom to Fe atom through the conjugated π bond of graphene is thermodynamically beneficial to the 4e − ORR. [ 82 ] The formation of an atom dimer between two single metal sites demonstrates another way to adjust the SACs active center's coordination environment. Lu et al.…”

One‐dimensional nanomaterial supported metal single‐atom electrocatalysts: Synthesis, characterization, and applications

“…Appropriate electronic modulation is another effective way to enhance the intrinsic catalytic activity by optimizing the adsorption energy of the metal atoms to the reactants and intermediates. [62] One common approach to alter the electronic structure of single-atom active centers is to introduce proper foreign atoms (e.g., B, N, O, S, and P) to tune their coordination environments via near-range coordination with nitrogen and long-range interaction with other heteroatoms. [63] In addition, hybrid catalysts have also been successfully fabricated to optimize their electronic structures by combining MSAs with low-cost transition metal nanoparticles or their carbides, showing superior catalytic activity comparable to commercial Pt-based materials.…”