Atomic Structure Modification of Fe‒N‒C Catalysts via Morphology Engineering of Graphene for Enhanced Conversion Kinetics of Lithium–Sulfur Batteries

Abstract

Single-atom M-N-C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen-coordinated mononuclear metal moieties (MN x moities) are bio-inspired active sites that are analogous to various metal-porphyrin cofactors. Given that the functions of metal-porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MN x active sites in heterogeneous M-N-C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN 4 moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN 4 moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with firstprinciples calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li 2 S redox step, is attributed to the local structure modified FeN 4 active sites, while increased specific surface area also contributes to improved performance at low C-rates. Owing to the synergistic combination of atomic-level modified FeN 4 active sites and morphological advantage of graphene support, Fe-N-C catalysts with wrinkled graphene morphology show superior lithium-sulfur battery performance at both low and high C-rates (particularly 915.9 mAh g −1 at 5 C) with promising cycling stability.

High spin Fe3+-related bonding strength and electron transfer for sensitive and stable SERS detection

“…The pre-edge peak at of MIL-101 is assigned to the 1s to 3d quadrupole transition of the octahedral geometric Fe atom 43 .The absorption edges of MIL-101(Fe), bimetallic MIL-101(FeNi) and trimetallic MIL-101(FeNiTi) are closer to that of Fe 2 O 3 reference and far away from Fe foil, suggesting the Fe species of these samples exist as cationic state (Figure 4a). Moreover, the k 3 -weighted Fourier-transformed extended X- EXAFS spectra show that Fe-O bond in bimetallic MIL-101(FeNi) and trimetallic MIL-101(FeNiTi) is longer than that in MIL-101(Fe) (Figure 4b), suggesting the octahedral geometry of Fe sites is distorted after the introduction of Ni and Ti elements 44 , which is also consistent with the XRD result. Besides, as presented in Ni K-edge the XANES spectra of Ni K-edge exhibits a slight shift towards higher energy (Figure 4c), suggesting Ni species with a higher valence state is formed from the introduction of Ti atoms 45 .…”

Oxygen-Plasma-Treated Fe–N–C Catalysts with Dual Binding Sites for Enhanced Electrocatalytic Polysulfide Conversion in Lithium–Sulfur Batteries

“…M–N–C single-atom catalysts (SACs) with nitrogen-coordinated metal atoms (MN x moiety) stabilized on a carbon matrix are a promising class of heterogeneous catalysts, designed to mimic the structure of metallo­enzymes in living organisms. − In analogy with nature’s elaborate methods to fine-control the catalytic properties, atomic-level tuning of heterogeneous M–N–C catalysts by regulating the local environment of MN x active sites has recently attracted attention. For example, changing the coordination environment or introducing heteroatoms near the MN x sites was proposed recently to enhance the catalytic activity of these materials for various demanding reactions. − However, fine modification of the environment surrounding the MN x site is still limited due to the unsophisticated carbonization process during the catalyst preparation. In addition, active-site tuning methods that might cause changes in porous structure or morphology of the catalyst could result in misguided understanding of the effect of modifying the local environment.…”

NbN nanodot decorated N-doped graphene as a multifunctional interlayer for high-performance lithium–sulfur batteries

“…The discharging procedure involves the conversion of soluble Li 2 S 4 , Li 2 S 6 and Li 2 S 8 to insoluble Li 2 S/Li 2 S 2 , making it difficult for the reaction to proceed quickly and sustainably. 66,67 In view of this, the Li 2 S nucleation experiments were performed to further understand the catalytic mechanism and validate the catalytic activity during the electrochemical reaction process. From the potentiostatic discharge profiles in Fig.…”