Coordination Sphere Research Articles

Oxygen Doping Cooperated with Co-N-Fe Dual-Catalytic Sites: Synergistic Mechanism for Catalytic Water Purification within Nanoconfined Membrane.

Atom-site catalysts, especially for graphitic carbon nitride-based catalysts, represents one of the most promising candidates in catalysis membrane for water decontamination. However, unravelling the intricate relationships between synthesis-structure-properties remains a great challenge. This study addressed the impacts of coordination environment and structure units of metal central sites based on Mantel test, correlation analysis and evolution of metal central sites. An optimized unconventional oxygen doping cooperated with Co-N-Fe dual-sites (OCN Co/Fe) exhibited synergistic mechanism for efficient peroxymonosulfate activation, which benefited from a significant increase in charge density at the active sites and the regulation in the natural population of orbitals, leading to selective generation of SO4 •-. Building upon these findings, the OCN-Co/Fe/PVDF composite membrane demonstrated a 33 min-1 ciprofloxacin (CIP) rejection efficiency and maintained over 96% CIP removal efficiency (over 24h) with an average permeance of 130.95 L m-2 h-1. Our work offers a fundamental guide for elucidating the definitive origin of catalytic performance in advance oxidation process (AOPs) to facilitate the rational design of separation catalysis membrane with improved performance and enhanced stability. This article is protected by copyright. All rights reserved.

Contemporary Assessment of Energy Degeneracy in Orbital Mixing with Tetravalent f-Block Compounds.

The f block is a comparatively understudied group of elements that find applications in many areas. Continued development of technologies involving the lanthanides (Ln) and actinides (An) requires a better fundamental understanding of their chemistry. Specifically, characterizing the electronic structure of the f elements presents a significant challenge due to the spatially core-like but energetically valence-like nature of the f orbitals. This duality led f-block scientists to hypothesize for decades that f-block chemistry is dominated by ionic metal-ligand interactions with little covalency because canonical covalent interactions require both spatial orbital overlap and orbital energy degeneracy. Recent studies on An compounds have suggested that An ions can engage in appreciable orbital mixing between An 5f and ligand orbitals, which was attributed to "energy-degeneracy-driven covalency". This model of bonding has since been a topic of debate because different computational methods have yielded results that support and refute the energy-degeneracy-driven covalency model. In this Viewpoint, literatures concerning the metal- and ligand-edge X-ray absorption near-edge structure (XANES) of five tetravalent f-block systems─MO2 (M = Ln, An), LnF4, MCl62-, and [Ln(NP(pip)3)4]─are compiled and discussed to explore metal-ligand bonding in f-block compounds through experimental metrics. Based on spectral assignments from a variety of theoretical models, covalency is seen to decrease from CeO2 and PrO2 to TbO2 through weaker ligand-to-metal charge-transfer (LMCT) interactions, while these LMCT interactions are not observed in the trivalent Ln sesquixodes until Yb. In comparison, while XANES characterization of AnO2 compounds is scarce, computational modeling of available X-ray absorption spectra suggests that covalency among AnO2 reaches a maximum between Am and Cm. Moreover, a decrease in covalency is observed upon changing ligands while maintaining an isostructural coordination environment from CeO2 to CeF4. These results could allude to the importance of orbital energy degeneracy in f-block bonding, but there are a variety of data gaps and conflicting results from different modeling techniques that need to be addressed before broad conclusions can be drawn.

Decoding Active Sites for Highly Efficient Semihydrogenation of Acetylene in Palladium-Copper Nanoalloys.

Accurately decoding the three-dimensional atomic structure of surface active sites is essential yet challenging for a rational catalyst design. Here, we used comprehensive techniques combining the pair distribution function and reverse Monte Carlo simulation to reveal the surficial distribution of Pd active sites and adjacent coordination environment in palladium-copper nanoalloys. After the fine-tuning of the atomic arrangement, excellent catalytic performance with 98% ethylene selectivity at complete acetylene conversion was obtained in the Pd34Cu66 nanocatalysts, outperforming most of the reported advanced catalysts. The quantitative deciphering shows a large number of active sites with a Pd-Pd coordination number of 3 distributed on the surface of Pd34Cu66 nanoalloys, which play a decisive role in highly efficient semihydrogenation. This finding not only opens the way for guiding the precise design of bimetal nanocatalysts from atomic-level insight but also provides a method to resolve the spatial structure of active sites.

Role of atomic substitution in first coordination shell of Fe–N–C single atom catalyst towards oxygen reduction reaction: A theoretical study

Due to structural complexity and limited understanding, precise chemical modification in atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts requires theoretical calculations to optimize electronic, geometric, and catalytic performance and experimental implementation of learned lessons to improve their catalytic performance towards oxygen reduction reaction (ORR). Herein, we conducted a density functional theory (DFT) investigation to understand the effect of the replacement of O-atoms in Fe–O4–C by N-atoms in the first coordination shell of Fe-site (constructing five models: Fe–O4–C, Fe–O3N–C, Fe–N2O2–C, Fe–ON3–C and Fe–N4–C) towards ORR. The geometric and electronic calculations of these models suggested that replacing all the O-atoms with N-atoms around the Fe-site would make it more conducive to the adsorption of ORR intermediates. Moreover, the Gibbs free energy calculations demonstrated that the Fe-site becomes the active centre for 2e− ORR, leading to the dominant generation of H2O2 when Fe is coordinated with four O-atoms (Fe–O4–C). Whereas in compounds like Fe–N2O2–C, Fe–O3N–C, and Fe–N4–C, where the Fe-site displays 4e− ORR, form water is a preferred product if the O-atoms are replaced by N-atoms, as in Fe–N2O2–C, Fe–O3N–C, and Fe–N4–C. This study would provide a fundamental understanding of how atomically dispersed M-N-C catalysts' electrocatalytic activity is affected by changes in the coordination environment of metal sites.

Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe3: Experiment and Calculation

This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe3. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe3 was solved in the space group Cmcm (a = 4.3086(3) Å, b = 14.3093(9) Å, and c = 11.1957(7) Å) with the KZrCuS3 structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe6]9−) form two-dimensional layers (Er(Te1)2/2e(Te2)4/2k−∞2), while distorted tetrahedra ([CuTe4]7−) form one-dimensionally connected substructures (Cu(Te1)2/2e(Te2)2/1t5−∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers (CuErTe32−∞2) between which Eu2+ ions are located in a trigonal-prismatic coordination environment (EuTe610−). The trigonal prisms are connected by faces, forming chains (Eu(Te1)2/2(Te2)4/22−∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh3 (Ch = S, Se, and Te)) and tellurides (EuLnCuTe3 (Ln = Gd, Er, and Lu)). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe3 were performed. The types and wavenumbers of fundamental modes were determined, and the involvement of ions in the IR and Raman modes was assessed. The experimental Raman spectra were interpreted. The telluride EuErCuTe3 at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh3 (Ch = S and Se)). Its experimental magnetic characteristics were close to the calculated ones. The decrease in the magnetic phase transition temperature in the series of the erbium chalcogenides was discovered.

Dimerization of Fe(III) Ion in an Aqueous Medium: Mechanistic Modelling and Effects of Ligands.

Aqueous iron solutions generally undergo spontaneous hydrolysis followed by aggregation resulting in the precipitation of nanocrystalline oxyhydroxide minerals. The mechanism of nucleation of such multinuclear oxyhydroxide clusters are unclear due to limited experimental evidence. Here, we investigate the mechanistic pathway of dimerization of Fe(III) ions using density functional theory (DFT) in aqueous medium considering effects of other ligands. Two hydrolyzed monomeric Fe(III) ions in aqueous medium may react to form two closely related binuclear products, the m-oxo and the dihydroxo Fe2 dimer. Our studies indicate that the water molecules in the second coordination sphere and those co-ordinated to the Fe(III) ion, both participate in the dimerization process. The proposed mechanism effectively explains the formation of dihydroxo and μ-oxo Fe2 dimers with interconversion possibilities, for the first time. Results show, with only water molecules present in the second co-ordination sphere, dihydroxo Fe2 dimer is the thermodynamically and kinetically favored product with a low activation free energy. We calculated the step-wise reaction free energies of dimerization in the presence of nitrate ions in the first and second coordination sphere of Fe(III) ion separately, which shows that with nitrate ions in the second co-ordination sphere, the μ-oxo Fe2 dimer formation iskinetically favored.

Carbene-Stabilized Phosphagermylenylidene: A Heavier Analog of Isonitrile.

Phosphagermylenylidenes (R-P═Ge), as heavier analogs of isonitriles, whether in their free state or as complexes with a Lewis base, have not been previously identified as isolable entities. In this study, we report the synthesis of a stable monomeric phosphagermylenylidene within the coordination sphere of a Lewis base under ambient conditions. This species was synthesized by Lewis base-induced dedimerization of a cyclic phosphagermylenylidene dimer or via Me3SiCl elimination from a phosphinochlorogermylene framework. The deliberate integration of a bulky, electropositive N-heterocyclic boryl group at the phosphorus site, combined with coordination stabilization by a cyclic (alkyl)(amino)carbene at the low-valent germanium site, effectively mitigated its natural tendency toward oligomerization. Structural analyses and theoretical calculations have demonstrated that this unprecedented species features a P═Ge double bond, characterized by conventional electron-sharing π and σ bonds, complemented by lone pairs at both the phosphorus and germanium atoms. Preliminary reactivity studies show that this base-stabilized phosphagermylenylidene demonstrates facile release of ligands at the Ge atom, coordination to silver through the lone pair on P, and versatile reactivity including both (cyclo)addition and cleavage of the P═Ge double bond.

Polymerized Network-Based Artificial Peroxisome Reprogramming Macrophages for Photoacoustic Imaging-Guided Treatment of Rheumatoid Arthritis.

Artificial peroxisomes (AP) with enzyme-mimetic catalytic activity and recruitment ability have drawn a great deal of attention in fabricating protocell systems for scavenging reactive oxygen species (ROS), modulating the inflammatory microenvironment, and reprogramming macrophages, which is of great potential in treating inflammatory diseases such as rheumatoid arthritis (RA). Herein, a macrophage membrane-cloaked Cu-coordinated polyphthalocyanine-based AP (CuAP) is prepared with a macrocyclic conjugated polymerized network and embedded Cu-single atomic active center, which mimics the catalytic activity and coordination environment of natural superoxide dismutase and catalase, possesses the inflammatory recruitment ability of macrophages, and performs photoacoustic imaging (PAI)-guided treatment. The results of both in vitro cellular and in vivo animal experiments demonstrated that the CuAP under ultrasound and microbubbles could efficiently scavenge excess ROS in cells and tissues, modulate microenvironmental inflammatory cytokines such as interleukin-1β, tumor necrosis factor-α, and arginase-1, and reprogram macrophages by polarization of M1 (proinflammatory phenotype) to M2 (anti-inflammatory phenotype). We believe this study offers a proof of concept for engineering multifaceted AP and a promising approach for a PAI-guided treatment platform for RA.

Recent Advances in Carbon-Based Single-Atom Catalysts for Electrochemical Oxygen Reduction to Hydrogen Peroxide in Acidic Media

Electrochemical oxygen reduction reaction (ORR) via the 2e− pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e−-ORR. Firstly, the reaction mechanism of 2e−-ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e−-ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e−-ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e−-ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process.

Schiff‐Base Aluminum Complexes as Bifunctional Catalysts for the Selective Ring‐Opening Co‐Polymerization of Cyclohexene Oxide and Succinic Anhydride

The ring‐opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is emerging as a powerful method for the synthesis of polyesters with innovative structures and properties. In this work, a series of dialkyl‐aluminum complexes stabilized by Schiff‐base ligands with different functional side arms (pyridine, amine, or phosphine) and different substituents on the phenoxy moieties have been synthetized and tested as catalysts in the ROCOP of cyclohexene oxide (CHO) and succinic anhydride (SA). The selectivity of the catalysts in the ROCOP was significatively depending on the nature of the pendant arm and/ or of the substituents of the ligand framework. The complexes designed to have a dynamic coordination sphere in which the side arms simulate the role of a neutral cocatalyst favored the desired selectivity, giving poly(CHO‐alt‐SA) with narrow dispersity and negligible ether linkage. NMR investigations and DFT calculations rationalized the observed behavior.

Role of N-Rich Coordination Environment in Metal–Organic Frameworks for Enhanced Photocatalytic Dye Degradation

Role of N-Rich Coordination Environment in Metal–Organic Frameworks for Enhanced Photocatalytic Dye Degradation

Highly efficient electrocatalysis of oxygen to hydroxyl radical by FeN2O2 single-atom catalyst for refractory organic pollutant removal

The heterogeneous electro-Fenton (Hetero-EF) provides an effective and environmentally friendly method for refractory pollutants removal by strongly oxidative •OH. However, the •OH generation shows an insufficient activity in activating H2O2 to •OH due to the too strong H2O2 binding on the catalytic site. Here, an iron single-atom FeN2O2 catalyst anchored on hollow spherical porous carbon (FeN2O2-HPC) was designed to enhance •OH production by modulating the H2O2 binding. The FeN2O2-HPC Hetero-EF system showed a •OH production rate of 25.0 μmol h−1 and kinetic rate constant of 2.06 h−1 for phenol removal, which exceeded the FeN4 catalyst (the most reported iron single-atom). Density function theory calculations revealed that FeN2O2 could lower the H2O2 adsorption energy and energy barrier of H2O2 activation to •OH compared with FeN4, thus enhancing •OH production. This work gives a new insight into the •OH generation enhancement of Hetero-EF by modulating single-atom coordination environment for refractory pollutants removal.

Cycloheptatrienyl-Bridged Triple-Decker Complexes.

The first structurally characterized organometallic multidecker sandwich complexes featuring a cycloheptatrienyl ring (Cht, C7H73-) in the coordination sphere are presented. The synthesis of inverse sandwich complexes of the rare earth elements YIII and ErIII with a bridging cycloheptatrienyl ligand of the type [(thf)(BH4)2LnIII(μ-η7:η7-Cht)LnIII(BH4)(thf)2] is described first. The subsequent introduction of the CotTIPS ligand (CotTIPS = 1,4-(iPr3Si)2C8H62-) into the coordination sphere of the rare earth cations resulted in the isolation of unprecedented triple-decker compounds with the formula [(thf)3K{(η8-CotTIPS)LnIII}2(μ-η7:η7-Cht)], bearing a seven-membered aromatic carbon ring as a middle deck. These compounds are also the first examples of rare earth triple-decker complexes not bridged by a Cot derivative, based on purely carbon-based ligands. The magnetic properties of the respective ErIII congeners were investigated in detail, leading to the observation of antiferromagnetic coupling of the ErIII cations and a blocking temperature of 13.5 K. The conversion of the YIII compound [(thf)3K{(η8-CotTIPS)YIII}2(μ-η7:η7-Cht)] with [YIII(Cot)I(thf)2] resulted in ligand rearrangement and the selective formation of the first triple-decker complex ([(η8-CotTIPSYIII)2(μ-η8:η8-Cot)]) featuring two Cot ligands with different substituents in its coordination sphere.

Surface-Grafted Single-Atomic Pt-Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor-Inducing Interfacial Electron Transfer.

Based on the electron-withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post-modification amide reaction was firstly used to graft it onto the surface of NH2-MIL-125, which formed a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precise control over the first coordination sphere of Pt single atoms was achieved using further post-modification with additional bipyridine to investigate the effect of Pt-Nx coordination numbers on reaction activity. The as-synthesized NML-PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g-1 h-1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2-MIL-125 and NML-PtN4, respectively. In addition, the superior apparent quantum yield of 4.01% (390 nm) and turnover frequency of 190.3 h-1 (0.78 wt% Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF-Molecule catalysts with efficient charge carrier separation and precise regulation of single-atom coordination sphere.

Surface‐Grafted Single‐Atomic Pt‐Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor‐Inducing Interfacial Electron Transfer

Based on the electron‐withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post‐modification amide reaction was firstly used to graft it onto the surface of NH2‐MIL‐125, which formed a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precise control over the first coordination sphere of Pt single atoms was achieved using further post‐modification with additional bipyridine to investigate the effect of Pt‐Nx coordination numbers on reaction activity. The as‐synthesized NML‐PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g−1 h−1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2‐MIL‐125 and NML‐PtN4, respectively. In addition, the superior apparent quantum yield of 4.01% (390 nm) and turnover frequency of 190.3 h−1 (0.78 wt% Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF‐Molecule catalysts with efficient charge carrier separation and precise regulation of single‐atom coordination sphere.

DFT Study on Effect of Metal Type and Coordination Environment on CO2 ECR to C1 Products over M-N-C Catalysts.

Electrocatalytic reduction (ECR) of CO2 to chemical products is an important carbon emission reduction method. This work uses DFT to study the stability of N-doped graphene-supported four metal single-atom catalysts (M-N-C) and the effects of the coordination environment and metal centers on the selectivity of CO2 ECR to C1 products. The results show that Fe, Co, Ni, and Cu have good stability. The coordination environment has a significant modulating effect on product selectivity, and the change of the number of ligand nitrogen atoms will affect the size of the potential-limiting step of each product. When the number of nitrogen ligands is the same, the different metal centers of the M-N-C catalyst have a significant effect on the selectivity of different products. In addition, the introduction of nitrogen atom ligands can adjust the electronic structure of the graphene-supported metal center, increase the d-band center of most metals, and improve the reaction activity.

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Innovative green intense tetra-eutectic solvent (ITES) for recovery via occlusion co-precipitation at room temperature

Lithium iron phosphate (LiFePO4) is the widely used cathode material for safe and high-power lithium-ion batteries (LIBs) for electric vehicles (EVs). Therefore, numerous challenges to re-manufacturing, re-use, and recovery from spent LiFePO4/C are tolerated if evaluated early in the innovation process. Herein, innovative green intense tetra-eutectic solvent (ITES) has been used to recover a new Li-metal co-intercalation compound from spent LiFePO4/C cathode material, which is simple and cost-effective. The ITES leaching concerning organic solution with active hydrogen donor-acceptor salts creates a coordination environment through occlusion co-precipitate new co-intercalation compound at room temperature. Innovative green ITES-10 solution has successfully recovered a new Li-metal co-intercalation regarding the active hydrogen donor-acceptor bonding coordination environment of ITES adequate leaching solution and proposed recovery mechanism. The ICP-MS value of recovery metal (7Li) efficiency (%) of ITES-10 leaching for spent LiFePO₄/C cathode materials reaches approximately 0.452% at room temperature for recovery of new co-intercalation compound, besides the fresh LiFePO₄/C cathode materials (as reference), approximately 0.805%, respectively. Therefore, innovative ITES is considered to recover spent Li-based cathode materials in our future works concerning high leaching recovery rates below 100 °C in experimental conditions.

Precise Modulation of the Coordination Environment of Single Cu Site Catalysts to Regulate the Peroxymonosulfate Activation Pathway for Water Remediation.

Single atom site catalysts (SACs) with atomically dispersed active sites can be expected to be potential ideal catalysts for accurately modulating the persulfate activation pathway during the water remediation process because of their well-defined structure and the maximum metallic atom utilization. In this paper, a series of Cu SACs with different coordination environments were synthesized to elaborately regulate the peroxymonosulfate activation pathway in AOPs to clarify active species generation and transformation in water remediation. The degradation rate constants (kobs) of Cu-N2, Cu-N3, and Cu-N4 were 0.028, 0.021, and 0.015 min-1, respectively. Cu-N2 SACs exhibited a noticeable enhanced performance for bisphenol A (BPA) removal from water compared to that of the Cu-Nx SACs (x = 3, 4), accompanied by peroxymonosulfate (PMS) activation pathway variation. As shown by experimental and theoretical results, the PMS activation pathway was transformed from ROS to electron transfer with nitrogen coordination numbers decreasing from 4 to 2, which can be ascribed to the uneven charge distribution of Cu sites as well as upshifts in the d-band center, and thereby optimized electron transfer for PMS activation. Furthermore, the increasing nitrogen vacancies of single Cu site catalysts can also result in more unoccupied 3d orbitals of Cu atoms in SACs, thereby improving the intermediates' (PMS and BPA) adsorption-desorption process and BPA removal performance. These findings provided a beneficial approach for the coordination number regulation of SACs in water remediation.

Single-atom Fe catalysts with pyrrolic-type FeN4 sites for efficient oxygen reduction reaction: Identifying the roles of different N species

Developing electrocatalysts with efficient cathode oxygen reduction reaction (ORR), for example, iron-based single-atom catalysts (Fe-SACs), has been deemed necessary to accelerate the commercialisation process of zinc (Zn)–air batteries. Nevertheless, determining how various nitrogen species and active metal centres coordinate on an atomic scale remains unclear and inadequately explained. Herein, we demonstrate a soft-template-aided technique using Fe-containing molecules (e.g. iron phthalocyanine [FePc], Fe-1,10-phenanthroline [Fe-Phen] and Fe-glucose) to enhance the performance of Fe-SACs in terms of ORR. In this technique, FePc molecules can be converted into atomically dispersed pyrrolic-type iron–nitrogen (FeN4) sites during a pyrolytic process. The resultant catalyst exhibits excellent ORR activity (half-wave potential = 0.90 V) in alkaline medium and standing battery performance when used in Zn–air batteries (peak power density = 197.3 mW cm−2 and specific capacity = 796.2 mAh g−1). As per the findings from control experiments and characterisation studies, electron transfer between the support and the active Fe centre amplifies the ORR performance. Theoretical calculations substantiate that Fe sites coordinated with pyrrolic N atoms govern the electronic configuration of the catalysis, reducing the free energy absorption of reaction intermediates and thus increasing its intrinsic ORR capability. Herein, we aim to offer a fresh perspective on the relation between coordination environments and catalytic activity in ORR catalysts.