Contracted Fe–N₅–C₁₁ Sites in Single-Atom Catalysts Boosting Catalytic Performance for Oxygen Reduction Reaction

Abstract

Promoting the catalyst performance for oxygen reduction reaction (ORR) in energy conversion devices through controlled manipulation of the structure of catalytic active sites has been a major challenge. In this work, we prepared Fe−N−C single-atom catalysts (SACs) with Fe−N 5 active sites and found that the catalytic activity of the catalyst with shrinkable Fe−N 5 −C 11 sites for ORR was significantly improved compared with the catalyst bearing normal Fe−N 5 −C 12 sites. The catalyst C@PVI-(TPC)Fe-800, prepared by pyrolyzing an axial-imidazole-coordinated iron corrole precursor, exhibited positive shifted half-wave potential (E 1/2 = 0.89 V vs RHE) and higher peak power density (P max = 129 mW/cm 2 ) than the iron porphyrin-derived counterpart C@PVI-(TPP)Fe-800 (E 1/2 = 0.81 V, P max = 110 mW/cm 2 ) in 0.1 M KOH electrolyte and Zn−air batteries, respectively. X-ray absorption spectroscopy (XAS) analysis of C@PVI-(TPC)Fe-800 revealed a contracted Fe−N 5 −C 11 structure with iron in a higher oxidation state than the porphyrin-derived Fe−N 5 −C 12 counterpart. Density functional theory (DFT) calculations demonstrated that C@PVI-(TPC)Fe-800 possesses a higher HOMO energy level than C@PVI-(TPP)Fe-800, which can increase its electron-donating ability and thus help achieve enhanced O 2 adsorption as well as O−O bond activation. This work provides a new approach to tune the active site structure of SACs with unique contracted Fe−N 5 −C 11 sites that remarkably promote the catalyst performance, suggesting significant implications for catalyst design in energy conversion devices.

Non-noble metal single-atoms for oxygen electrocatalysis in rechargeable zinc–air batteries: recent developments and future perspectives

“…3a–d). 97 Li and co-workers also proved that the Fe–N 5 active sites with the asymmetric electron depletion zone over the metal center can improve the activation of intermediates and decreased the energy barrier of the rate-determining step (Fig. 3e–g), which thus accelerated the intrinsic ORR and OER processes, leading to a superb battery performance.…”

PGM-free single atom catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells

“…Local coordination manipulation, which involves altering the type and number of ligand atoms, modulates the electronic structure of the metal center, including electron density and d-orbital occupancy. 63–70 Such regulation can influence the adsorption capacity of the metal center for reactants and the activation energy, creating active sites with specific geometric configurations that may be more favorable for the transition states of particular reactions, thereby reducing the reaction energy barrier and improving reaction kinetics and catalytic activity. Zhang et al demonstrated that modulating the spatial distance between phosphorus doping atoms and single-atom iron sites can enhance ORR activity, thereby revealing the inductive effect between single-atom sites.…”

Efficient Bifunctional NiFe-LDH@Co9S8 Nanoflower Electrocatalysts Anchored with Pt Nanocrystal for Flexible Quasi-solid Rechargeable Zinc Air Battery

“…Layered double hydroxides (LDHs), known as a benchmark for OER activity, have attracted great focus for water splitting and metal-air batteries. − Nevertheless, during the synthesis procedure, agglomeration and lower conductivity plague pristine LDHs and, hence, their electrochemical active surface area (ECSA) will decrease. , Meanwhile, the lack of ORR catalysis indicates that a single LDH fails to satisfy the requirement of a catalyst for RZABs. Therefore, constructing hierarchical structures that combine LDHs with conductive ORR active material is considered an effective solution .…”