Mn Valence Research Articles

High-Entropy Layered Oxide Cathode Materials with Moderated Interlayer Spacing and Enhanced Kinetics for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) with low cost and environmentally friendly features have recently attracted significant attention for renewable energy storage. Sodium layer oxides stand out as a type of promising cathode material for SIBs owing to their high capacity, good rate performance, and high compatibility for manufacturing. However, the poor cycling stability of layer oxide cathodes due to structure distortion greatly impacts their practical applications. Herein, a high entropy doped Cu, Fe, and Mn-based layered oxide (HE-CFMO), Na0.95Li0.05Mg0.05Cu0.20Fe0.22Mn0.35Ti0.13O2 for high-performance SIBs, is designed. The HE-CFMO cathode possesses high-entropy transition metal (TM) layers with a homogeneous stress distribution, providing a moderated interlayer spacing to maintain the structure stability and enhance Na+ ion diffusion. In addition, Li doping in TM layers increases the Mn valence state, which effectively suppresses John-Teller effect, thus stabilizing the layered structure during cycling. Furthermore, the use of nontoxic and low-cost raw materials benefits future commercialization and reduces the risk of environmental pollution. As a result, the HE-CFMO cathode exhibits a super cycling performance with a 95% capacity retention after 300 cycles. This work provides a promising strategy to improve the structure stability and reaction kinetics of cathode materials for SIBs.

Smaller rare-earth cation and mixed valent Mn incorporation as a dual strategy to enhance ferrimagnetic ordering temperatures in A-site ordered quadruple perovskites, LnCu3Mn1+xTi3-xO12 (Ln = La, Nd; x = 0, 0.3).

High-TC ferro-/ferrimagnetic quadruple perovskites constitute an important class of oxides that has garnered a lot of research attention in recent times, but their synthesis is commonly achieved under high-pressure conditions. Thus, the development of high-TC quadruple perovskites that can be synthesized under ambient pressure can be a key to the above problem. Herein, we report ambient pressure synthesis of a series of new A-site ordered quadruple perovskites, LnCu3Mn1+xTi3-xO12 (Ln = La, Nd; x = 0, 0.3), by coupled aliovalent-cation manipulation in CaCu3Ti4O12. The effect of smaller lanthanide Nd incorporation in place of La has been investigated. Furthermore, 30% mixed valency of Mn per Mn3+ has been introduced in place of Ti4+ following similar strategies adopted to achieve giant magnetoresistive manganites La0.7A0.3MnO3 (A = Ca, Sr, Ba) from LaMnO3. Mn is present in the 3+ state for x = 0 and in a mixed valent state (3+ and 4+) for x = 0.3, whereas Cu exists in the 2+ state in all the compounds. While LaCu3MnTi3O12 and LaCu3Mn1.3Ti2.7O12 show the onset of ferrimagnetic order at ∼60 and 110 K, respectively, the corresponding Nd analogs, NdCu3MnTi3O12 and NdCu3Mn1.3Ti2.7O12, exhibit enhanced TC's of ∼80 and 140 K, respectively. This work reveals an effective strategy of mixed-valent Mn incorporation in the B-sublattice and smaller rare-earth cation incorporation to achieve higher ferrimagnetic ordering temperatures in quadruple perovskites.

Selection of high rate capability and cycling stability MnO anode material for lithium-ion capacitors: Effect of the carbon source

The N-doped carbon modified MnO composites were successfully prepared using K2MnO4 as the manganese source, CH4N2O as the nitrogen source, and glucose, sucrose, or reduced graphene oxide as the carbon sources. Among them, the composite (MPN) prepared using glucose as the carbon source exhibited excellent electrochemical performance, attributed to its relatively small particle size (6.4 nm), high specific surface area of 199.4 m2·g−1, and a high ID/IG ratio of 0.86. The MnO in MPN contained a significant amount of Mn3+, ∼16.8 %, which is ascribed to the incomplete reduction of high valence Mn during the process of synthesis. With the formation of Mn3+, a large number of cationic vacancies were generated, which increased the diffusion coefficient of Li+ from 2.12 × 10−14 cm2 s −1 to 5.94 × 10−13 cm2 s−1. The carbon layer with appropriate thickness, doped N and mesoporous structure suitable for electrolyte transport provide a fast ion/electron transport channels for MnO, and ensure a stable interface structure in the electrochemical reactions. Consequently, the MPN anode material exhibited remarkable high current discharge capacity (769.5 mAh·g−1 at a high current density of 2 A·g−1) and excellent cycling performance (882.2 mAh·g−1 after 200 cycles at 1 A·g−1), indicating its exceptional rate performance and cycle stability. Furthermore, the lithium ion capacitor constructed with MPN as anode and activated carbon as cathode demonstrated a high specific energy of 190 Wh·kg−1, a high specific power of 205.3 W·kg−1, and an impressive cycling lifespan of up to 3000 cycles without obvious degradation.

A stable ZnMn2O4 cathode for aqueous Zn-ion batteries via Ni doping to suppress Mn dissolution

ZnMn2O4 (ZMO) emerges as a promising cathode for aqueous Zn-ion batteries due to its high theoretical capacity of 224 mAh g−1 and operating voltage of ∼1.9 V (vs. Zn2+/Zn). However, it suffers from capacity degradation over cycling, attributed to the dissolution of redox-active Mn through Mn3+ disproportionation. In this study, we propose a strategy to stabilize ZMO cathodes by transforming Mn3+ into Mn4+ via Ni doping, aiming for charge balance. The ZnMn2−xNixO4 (x = 0, 0.5, 1.0, and 1.5) with different Ni amounts was prepared by straightforward precipitation and calcination. The mitigation of redox-active Mn dissolution enhanced the specific capacity of all Ni-doped ZMO compared to 201 mAh g−1 of ZMO. ZnMn1.5Ni0.5O4 and ZnMnNiO4 exhibit 277 and 278 mAh g−1, respectively, surpassing ZMO’s theoretical capacity (224 mAh g−1) of ZMO. This additional capacity was attributed to MnOx deposition on the cathode and the charge storage reaction with Zn-ion within the MnOx deposit. Furthermore, Ni doping induces a structural transition of the tetragonal into a cubic spinel, expanding the unit cell volume. This structural modification combined with suppressed Mn dissolution contributes to improved cycling stability. ZnMnNiO4 exhibits 80 % retention of initial capacity after 1000 cycles, outperforming ZMO (57 % retention). The expanded unit cell reduces repulsion between inserted Zn ions, enabling a higher rate performance than pure ZMO. The change in Mn valence states induced by Ni doping enhanced the lifespan and rate capability of ZMO cathodes, underscoring their potential as cathodes for Zn-ion batteries.

Regulating the Manganese Valence State Improves the Kinetic Properties of Manganese‐Based Cathodes

AbstractManganese (Mn)‐based lithium (Li)‐ion batteries with high energy density and low cost have recently attracted considerable attention. One drawback of Mn‐based batteries is the severe capacity attenuation caused by the Jahn‐Teller effect, which distorts the crystal structure and reduces the kinetics of Li‐ion insertion/extraction in the cathodes. In this study, the Mn valence state is regulated on the surface of Mn‐based oxide particles and oxygen vacancies are introduced to facilitate rapid Li‐ion transport and charge storage by adding succinonitrile (SN) to Mn‐based cathodes. Because of the reaction between SN and Mn‐based cathode particles, the contents of Mn3+ ions and oxygen vacancies increase, leading to an improvement in the Li‐ion kinetic properties of the cathodes as well as a reduction in the dissolution of Mn from the cathodes. By regulating the Mn valence state, Li‐ion and Li metal batteries with LiMn2O4 or Li‐rich Mn‐based layered oxide cathodes show significantly enhanced discharge capacity and improved cyclic performance. This study demonstrates that regulating the valence state of Mn ions is an effective strategy for enhancing the electrochemical performance of Mn‐based Li batteries and that adding SN to the cathodes is a cost‐effective method for mass production.

Effect of Cu(II) and Conserved Copper Binding Sites onthe Multicopper Oxidase CopA and Characterization ofBioMnOx.

The microbial manganese removal process is believed to consist of the catalytic oxidation of Mn(II) by manganese oxidase. In this study, the multicopper oxidase CopA was purified and exhibited high manganese oxidation activity in vitro, and it was found that Cu(II) can significantly enhance its manganese oxidation activity. Gene site-directed mutagenesis was used to mutate four conserved copper binding sites of CopA to obtain four mutant strains. The manganese removal efficiencies of the four strains were determined, and it was found that H120 is the catalytically active site of CopA. The loss of Cu(II) and the mutation of the conserved copper binding site H120 resulted in the loss of ethoxyformyl and quinone modifications, a reduction in the number of modifications, and a change in the position of modifications, eventually causing a decrease in protein activity from 85.87% to 70.1%. These results reveal that Cu(II) and H120 play an indispensable role in manganese oxidation by the multicopper oxidase CopA. X-ray photoelectron spectroscopy (XPS) analysis indicates that biogenic manganese oxides produced by strains and by CopA were both composed of MnO2 and Mn3O4 and that the average valence of Mn was 3.2.

Degradation of toxic components in kitchen waste during hydrothermal carbonization process

Hydrothermal carbonization (HTC) is a promising technique for kitchen waste (KW) disposal. However, KW may contain heavy metals (HMs), aflatoxin, nitrites and sulfites, posing risk for hydrochar utilization. In order to clarify the migration of these toxic components during hydrochar formation process, 7 kinds of kitchen wastes were adopted to carry out HTC experiments at 180–240 °C. Concentration detections results showed that Fe, Mn, Cr, Ni, Cu, and Zn contents were relatively high with a range of 30–2500 mg/kg in KW feedstocks. After HTC treatment, Fe, Cr, Cu were mainly (>80 %) enriched in hydrochar, the enrichment factors of Mn, Ni, Zn was almost above 50 %. From the perspective of species and valence distributions, Mn, Fe, Ni, and Zn in hydrochar were below moderate risk level. No aflatoxin was detected in hydrochar, because AFB1 and AFB2 can be completely degraded into organic acids in the HTC environment at 180 °C. Part benzene rings in aflatoxin were reduced and the C-C bonds were further broken, the C-O bonds were oxidized to produce carboxylic acids. Some benzene rings in aflatoxin remained to form organic acids with aromatic structures. NO2− and SO32- ions with strong ecotoxicity were mostly converted into NO3− and SO42- and flowed into the liquid phase. Some NO2− ions were also converted to and ammonia N and pyridine N; some SO32- ions were converted to sulfonic and sulfinic acid organics, which were successively transformed into sulfonyl/sulfinyl and sulfone/sulfoxide organics. The above findings are of great significance for the transformation mechanism of toxic substances in HTC environment and environment-friendly utilization of hydrochar.

Exploring the dynamic evolution of lattice oxygen on exsolved-Mn2O3@SmMn2O5 interfaces for NO Oxidation

Lattice oxygen in metal oxides plays an important role in the reaction of diesel oxidation catalysts, but the atomic-level understanding of structural evolution during the catalytic process remains elusive. Here, we develop a Mn2O3/SmMn2O5 catalyst using a non-stoichiometric exsolution method to explore the roles of lattice oxygen in NO oxidation. The enhanced covalency of Mn–O bond and increased electron density at Mn3+ sites, induced by the interface between exsolved Mn2O3 and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn3+ sites. Near-ambient pressure X-ray photoelectron and absorption spectroscopies show that the activated lattice oxygen enables reversible changes in Mn valence states and Mn-O bond covalency during redox cycles, reducing energy barriers for NO oxidation and promoting NO2 desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn2O3/SmMn2O5 exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al2O3 catalyst.

Synergistic effects of haematite/hausmannite anchored graphene hybrids in high-energy density asymmetric supercapacitors

Addressing the critical demand for advanced energy storage systems (ESSs) amid escalating global energy needs and population growth, this study pioneers the synthesis of graphene-supported haematite and hausmannite (Gr@Mn3O4@Fe2O3/NF) ternary composite cathodes. These cathodes are tailored for high-performance asymmetric supercapacitors (ASCs), leveraging an economically viable process of fabrication. This innovation represents a significant leap forward, employing cost-effective techniques without compromising efficiency. Synchrotron X-ray absorption spectroscopy (XAS) analysis reveals a distinct blend of Fe and Mn valences, confirming the composite's unique structure. Electrochemical assessment underscores the superior capability of the electrodes, registering an unprecedented specific capacitance of ∼854 F/g in aqueous electrolytes, far surpassing traditional electrodes. Additionally, the composite electrodes maintain ∼70 % capacitance retention and about ∼94 % coulombic efficiency under a high current density of 4 A/g. In an ASC configuration, pairing the Gr@Mn3O4@Fe2O3/NF cathode with an anode made of AC, the ASC achieves the highest capacitance of ∼139 F/g, an energy density of ∼156.3 Wh/kg at a power density of ∼1439 W/kg, coupled with outstanding cyclability in a 1.5 V. This research delineates a scalable pathway for fabricating cost-efficient, high-energy density SCs, heralding a new era of portable electronic devices with enhanced energy storage capabilities.

Performance and Mechanism of Co and Mn Loaded on Fe-Metal-Organic Framework Catalysts with Different Morphologies for Simultaneous Degradation of Acetone and NO by Photothermal Coupling.

VOCs can be used instead of ammonia as a reducing agent to remove NO, achieving the effect of removing VOCs and NO simultaneously. Due to the high energy consumption and low photocatalytic efficiency required for conventional thermocatalytic purification, photothermal coupled catalytic purification can integrate the advantages of photocatalysis and thermocatalysis in order to achieve the effect of pollutants being treated efficiently with a low energy consumption. In this study, samples loaded with Co and Mn catalysts were prepared using the hydrothermal method on Fe-MOF with various morphologies. The catalytic performance of each catalyst was analyzed by studying the effects of their physicochemical properties through various characterizations, including XRD, SEM, BET, XPS, H2-TPR, TEM and O2-TPD. The characterization results demonstrated that the specific surface area, pore volume, high valence Co and Mn atoms, surface adsorbed oxygen and the abundance of oxygen lattice defects in the catalysts were the most critical factors affecting the performance of the catalysts. Based on the results of the performance tests, the catalysts prepared with an octahedral-shaped Fe-MOF loaded with Co and Mn showed a better performance than those loaded with Co and Mn on a rod-shaped Fe-MOF. The conversions of acetone and NO reached 50% and 64%, respectively, at 240 °C. The results showed that the catalysts were capable of removing acetone and NO at the same time. Compared with the pure Fe-MOF without Co and Mn, the loaded catalysts showed a significantly higher ability to remove acetone and NO simultaneously under the combination of various factors. The key reaction steps for the catalytic conversion of acetone and NO on the catalyst surface were investigated according to the Mars-van Krevelen (MvK) mechanism, and a possible mechanism was proposed. This study presents a new idea for the simultaneous removal of acetone and NOx by photothermal coupling.

Analysis of mercury removal and sulfur resistance of CrOx-MnOx-SnOx-TiO2 catalysts

To investigate the ability of CrOx-MnOx-SnOx-TiO2 composite catalysts to adsorb and remove substances, particularly in the presence or absence of SO2, Sn was included in CrMnTi catalysts throughout the production procedure. The incorporation of Sn was found to boost the specific surface area, optimize the pore structure, and augment the number of active sites, as determined using characterization methods such as XRD, XPS, and BET. When Sn metal oxides were included in MnTi catalysts individually, the resulting MnSnTi catalysts showed a limited capacity to remove Hg0. However, adding Sn metal oxides allowed for widening the temperature range in which the catalysts found successful application. This will increase the range of application temperature and is of very successful importance for large-scale commercial applications. They demonstrate that, by incorporating chromium metal oxides, the oxygen Oβ reactivity within the MnSnTi catalyst increases, resulting in a greatly improved capacity for Hg0 removal and its resistance to sulfur. This study details the combined effect of Cr, Mn, and Sn ternary composite oxides on sulfur resistance and mercury removal. The result shows that Sn promotes the strengthening of both the physical properties of the catalyst and the adsorption of mercury while also assisting in the dispersion of the catalyst. Cr enhances the ability of the catalyst to transfer electrons while in oxidation and, at the same time, favours the remaining high valence of Mn. Mn supports the catalyst for oxidizing mercury by changing its multivalent state. The CrMnSnTi catalysts have exceptional efficacy in removing mercury and possess excellent resistance to sulfur, making them an ideal catalytic option for industrial demercury removal. The catalysts exhibited excellent efficacy in removing mercury and showed strong sulfur resistance.

Synergistic effect to unlock the activity and stability for oxygen evolution reaction in spinel LiMn2O4 via d-block metal substitution

An effective strategy using d-block metal hybridization was proposed to induce electronic interaction and promote the synergistic effect, aiming to enhance the OER performance of cost-effective spinel LiMn2O4. Indeed, we deployed a series of LiNixMn2-xO4 catalysts substituted with Ni, yielding the increase of Mn valence states from Mn3.5+ to Mn4+. The LiNi0.5Mn1.5O4 catalyst achieved an excellent OER performance in alkaline media, with an overpotential reduction more than 320 mV at 10 mA cm−2 compared to the unsubstituted LiMn2O4, as well as the electrochemical stability. It was shown to be superior to the most reported Mn-based oxides OER electrocatalysts. Theoretical calculations demonstrated that Ni doped holes in the Mn site, leading to an increase in Mn4+, and that the shared covalent network of Ni 3d-O 2p-Mn 3d optimized an easier desorption of intermediates. These results pave a new example for modulating the chemisorption strength, thus enabling activating the activity and stability of OER process for cost-effective electrocatalysts based on spinel Mn oxides.

Multienzyme-Like Polyoxometalate-Based Single-Atom Enzymes for Cancer-Specific Therapy Through Acid-Triggered Nontoxicity-to-Toxicity Transition.

Single-atom enzymes (SAzymes) exhibit great potential for chemodynamic therapy (CDT); while, general application is still challenged by their instability and unavoidable side effects during delivery. Herein, a manganese-based polyoxometalate single-atom enzyme (Mn-POM SAE) is first introduced into tumor-specific CDT, which exhibits tumor microenvironment (TME)-activated transition of nontoxicity-to-toxicity. Different from traditional POM materials, the aggregates of low-toxic Mn-POM SAE nanospheres are obtained at neutral conditions, facilitating efficient delivery and avoiding toxicity problems in normal tissues. Under acid TME conditions, these nanospheres are degraded into smaller units of toxic Mn(II)-PW11; thus, initiating cancer cell-specific therapy. The released active units of Mn(II)-PW11 exhibit excellent multienzyme-like activities (including peroxidase (POD)-like, oxidase (OXD)-like, catalase (CAT)-like, and glutathione peroxidase (Gpx)-like activities) for the synergistic cancer therapy due to the stabilized high valence Mn species (MnIII/MnIV). As demonstrated by both intracellular evaluations and in vivo experiments, ROS is generated to cause damage to lysosome membranes, further facilitating acidification and impaired autophagy to enhance cancer therapy. This study provides a detailed investigation on the acid-triggered releasing of active units and the electron transfer in multienzyme-mimic-like therapy, further enlarging the application of POMs from catalytical engineering into cancer therapy.

Degradation of enrofloxacin with natural manganese oxides and enhancement by manganese oxidizing bacteria

Natural manganese oxides (n-MnOx) widely exist in the nature and may contribute to the elimination of organic contaminants. The present study investigated the degradation of frequently detected fluoroquinolone antibiotic enrofloxacin (EFX) and the degradation kinetics were analyzed. During the reaction, the valence of Mn in n-MnOx changed with the release of Mn ions. It was also found that combing manganese oxidizing bacteria with n-MnOx can enhance the degradation of EFX and alter the degradation pathway as well. The transformation products of EFX were analyzed with UPLC-MS/MS, which revealed seven products. Based on them, it is proposed that the degradation may start with the dehydrogenation from the piperazine moiety that was further broken down. Respirometry tests demonstrated that the degradation with n-MnOx significantly reduced the toxicity of EFX. This study proved the oxidation with n-MnOx as a simple and effective technology to remediate the contamination of enrofloxacin and other fluoroquinolones and the potential of combing the special capacity of microorganisms.

Comparative study of Mn oxide catalysts on toluene oxidation: The effect of Mn valence electronic structures

Understanding the structure-activity relationship of Mn-based oxide catalysts is of great importance for the rational development of highly performance catalysts for VOCs catalytic oxidation. However, the knowledge of the electronic structure-catalytic oxidation activity relationship over Mn-based oxide catalysts is still limited. Herein, we investigated the typical MnxOy (Mn3O4, MnO2, and Mn2O3) with different valence electronic structures by using various characterizations and DFT calculations. The MnO2 exhibits superior intrinsic activities (RS, 1.14×10−9 mol·m−2·s−1) when compared with Mn3O4 (0.54×10−9 mol·m−2·s−1) and Mn2O3 (0.45×10−9 mol·m−2·s−1) for toluene catalytic oxidation. The solid experimental and DFT calculation results show that the d-band center of Mn determines the intrinsic activity. The superior catalytic oxidation activity of MnO2 can be attributed to its higher d-band center (-1.03 eV) in comparison with that of Mn3O4 (-1.25 eV) and Mn2O3 (-1.59 eV). The higher d-band center can weaken the surface Mn-O bonds strength (k = 290.9 N/m) and strengthen the gaseous O2 adsorption simultaneously, then enhancing the mobility of surface lattice oxygen and the amount of adsorbed oxygen species. This work firstly reveals the intrinsic relationship between catalytic oxidation activity and d electronic structure over Mn-based oxide catalysts and provides knowledge that will advance the design of high-performance catalysts for catalytic oxidation.

Superoxide radical-induced rapid valence cycling of Mn(II/III/IV) for efficient degradation of organic pollutants

Transition metal oxides are one of the commonly used catalysts for ozone oxidation, and the slow redox cycling of different valence metal components inside the catalysts currently becomes a key bottleneck limiting their catalytic activity. In this work, the superoxide radicals generated at the N/C sites were used to reduce the neighboring high-valence metal components to low-valence states to construct a new mechanism for the rapid cyclic transition of Mn (II/III/IV) valence states. What's more, N/C sites enhanced the ozone adsorption and conversion ability, synergized with the adjacent MnO2 sites to generate interfacial hydroxyl radicals and superoxide radicals, and effectively inhibited the quenching effect of inorganic salt ions (e.g., Cl-, SO42-) on the free radicals. For the actual printing and dyeing wastewater, the COD (chemical oxygen demand) removal rate was as high as 70 % in 60 min and remained stable in 10 cycles with almost no manganese ions leaching. In addition, characterization such as EPR combined with DFT calculations showed that the dual-site structure significantly increased the oxygen vacancy content and Lewis acidity, and the synergistic interaction between graphite N and MnO2 was the most favorable for ozone conversion with the lowest reaction energy barriers.

Tuning the metal-insulator transition temperature by the controlled generation of oxygen vacancies on La0.7Ca0.3MnO3-x epitaxial thin films

This report presents a study on the effect of the controlled generation of oxygen vacancies on the electronic transport properties of La0.7Ca0.3MnO3-x epitaxial thin films. Oxygen defects cause significant changes in the crystalline structure of mixed-valence manganites and lower the Mn valence, resulting in a shift of the metal-insulator transition to lower temperatures due to modifications in the angles and lengths of Mn-O bonds. Experiments using Polarized Extended X-Ray Absorption Fine Structure Spectroscopy have provided strong evidence that oxygen vacancies are mainly formed in the basal plane of the MnO6 octahedra. The accurate control of oxygen vacancies generation opens possibilities for managing and enhancing the magneto-electronic properties of epitaxial manganite thin films with potential in industrial applications.

Site-substitution in GdCrO3: Effects of Mn valence states on structural, magnetic and electric properties

GdCr1-xMnxO3 (0 ≤ x ≤ 0.3) was prepared by sol-gel method, the effect of Mn doping on the microstructure, magnetic and electric properties of GdCrO3 were studied. The results indicate that all samples have a good orthogonal perovskite structure. The main diffraction peak and lattice parameter varied non-monotonically with the increase of Mn ions in XRD. This is related to the change in valence state of Mn ions, which has been confirmed by X-ray photoelectron spectroscopy (XPS). The positron annihilation lifetime spectrum indicates that vacancy defects and local electron density are related to the valence states of Mn ions. It can be noted from UV-Vis spectroscopic measurements that the doping of Mn ions leads to a decrease in the optical band gap (Eg) from 3.11 eV to 2.13 eV for GdCrO3. The temperature dependence curve of the magnetization intensity curves show that TN(Cr) decreases with Mn ions. The nonmonotonic variations of magnetic moment and remanent magnetization strength are associated with the valence state of Mn ions and the magnetic interactions after doping, respectively. In addition, the samples have low dielectric constants at low doping and the reverse at high doping, which is also related to the valence state variation of Mn ions.

Efficient and Stable Dual-Active-Site of Core-Shell NiFe-Layered Double Hydroxide Anchored on FeMnON-N-Doped Carbon Nanotubes as Bifunctional Oxygen Electrocatalysts for Zn-Air Batteries

The bifunctional air electrodes with numerous dual-active sites and low cost are desirable to modify the performance of Zn-air batteries (ZABs). Metal–oxygen-nitrogen–carbon substrate (M = Mn, Fe, Ni, etc.) and NiFe-layered double hydroxide (NiFe-LDH) nanosheets are excellent catalysts in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, respectively. Hereby, we investigate a bifunctional electrocatalytic substrate with a 3D core–shell hierarchical architecture by anchoring high OER-active NiFe-LDH on ORR-active FeMnZIF-8@gC3N4-derived FeMnON-N doped carbon nanotubes bamboo like (NiFe-LDH@FeMnON-NC). This nanocomposite has unique features such as robust synergistic effects, high conductivity, balance, and optimization of surface chemical valences of Fe, Mn, and Ni atoms to boost the bifunctional ORR and OER properties and stability in ZABs. The NiFe-LDH@FeMnON-NC nanocomposite not only exhibited superior OER electroactivity with a low onset overpotential of 235 mV (10 mA cm−2) but also had excellent ORR activity with a current density of −5.48 mA cm−2 and onset potential of 1.04 V, which is better than or comparable to those of commercial Pt/C and RuO2. Rechargeable ZABs constructed by bifunctional NiFe-LDH@FeMnON-NC have a peak power density (235.41 mW cm−2), open-circuit potential (OCV) (1.53 V), small discharge/charge band gap of 0.74 V and excellent discharge stability.

Enhanced ferromagnetic properties achieved by F-doping in BaFe1-xMnxO3-δ.

Tailoring the crystal structure, spin, and charge state of perovskite oxides through fluorine ion doping is an attractive and effective strategy, which could significantly modify the physical and chemical properties of base oxides. Here, BaFe1-xMnxO3-δ (x = 0, 0.1, 0.2, 0.3) and BaFe1-xMnxO2.9-δF0.1 (x = 0.1, 0.2, 0.3), belonging to 6H-type BaFeO3-δ, are prepared and investigated to evaluate the impact of F- doping. The distortion of crystal structure and the reduced average valence of Mn and Fe confirm the preference for F- substitution in the hexagonal layer, which are found as the key factors for the improved magnetic properties, including ferromagnetic ordering temperature, coercive force, and remanent magnetization. Moreover, the valence reduction of B-site ions and the increased resistance distinctly indicate the expense of electron hole via fluorine doping. This work describes the adjustment of crystal structure, electronic configuration, and ferromagnetic performance by simple F- doping, which provides a prospect for practical magnetic materials.