ZnMn2O4 Research Articles

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.

Improving H2 gas sensing with ZnMn2O4/Polypyrrole Nanocomposite

Here we report the operation of p-p heterojunction for improving the H2 gas sensing performance of ZnMn2O4/Polypyrrole nanocomposite (PZ) at room temperature. ZnMn2O4 (ZM) with a unique cubic morphology and porous architecture was synthesized via a one-step hydrothermal method. Polypyrrole (PPy) fibers and PZs were prepared through chemical oxidative polymerization of pyrrole monomers in the absence and presence of different weight percentages (wt%) of ZM, respectively. Our findings show that the PZs consisted of microcubic ZMs with dimensions of approximately 8 μm, covered with wire-like PPy fibers. The partial protonated PPy and different wt% of microcubic ZM have a significant effect on H2 gas sensing. The response of our hand-made sensor increased with increasing wt% of ZM and gas level. The PZ samples exhibited the highest response of 1.23 (the lowest tres value of 21.6 s) at a concentration of 15000 (2500) ppm H2 gas. Furthermore, the PZ sample contains 10 wt% of ZM demonstrated excellent long-term stability in response after six months, which indicates the accuracy and reliability of the sensor. H2 gas mechanism of the PZ sensor was studied in details. The advantage of p-p heterojunction could provide a new perspective for H2 gas sensing applications.

Zinc manganite as an efficient battery-grade material for supercapattery devices

In the current context, supercapatteries emerge as highly desirable candidates capable of merging both energy and power density within a single device. Battery-type metal oxide materials, combined with capacitive-based materials, stand out as promising candidates for high-performance supercapatteries. This investigation centers on the synthesis of nanocrystalline ZnMn2O4 (ZMO) and CoMn2O4 (CMO) through a straightforward hydrothermal method, followed by their physico-electrochemical characterization. Electrochemical analysis reveals that ZMO exhibits notably enhanced charge storage capability compared to CMO. This superiority can be attributed to favourable electro-structural properties, and stable redox chemistry of ZMO. The real-time performance of ZnMn2O4 was further assessed by fabricating a hybrid asymmetric supercapattery device (ZnMn2O4||NrGO), which achieves a specific capacity of 232 C g−1 at a current density of 1 A g−1. The hybrid asymmetric device underwent rigorous stability testing for 4000 cycles at a current density of 2 A g−1, showcasing remarkable performance with a 92 % retention of its initial capacity. The device demonstrated a power density of 980 W kg−1 and an energy density of 63 Wh kg−1, highlighting its considerable promise in the field.

Surface oxygen vacancies induced by cu-doping in hexagonal ZnMn2O4 nanoplates for high efficiency photothermocatalytic oxidation of toluene

The exploitation of efficient and stable photothermal catalyst for the deep mineralization of volatile organic compounds (VOCs) is crucial and challenging. Herein, a photothermal catalyst with abundant oxygen defects was prepared for the first time via Cu-doped ZnMn2O4 hexagonal nanoplate. Experimental characterization results reveal that Cu doping enhances not only the ZnMn2O4 defect contents but also the light absorption and thermal conversion ability of ZnMn2O4. Compared to the undoped ZnMn2O4 (ZMO), the ZnMn2O4 with optimal Cu doping amount (ZMO-4Cu) exhibits excellent photothermal catalytic performance (94% toluene conversion and 87% toluene mineralization) and good resistance to low concentration SO2 under full-spectrum light irradiation. Experimental characterizations and theoretical calculations jointly demonstrated that the oxygen vacancies of ZMO-4Cu surface are more conducive to the adsorption of O2, effectively reduce the oxygen dissociation energy of ZMO-4Cu, thus generating abundant active oxygen species and improving the photothermal catalytic activity for toluene oxidation. In situ IR experiments disclosed that photothermal catalysis is more conducive to the toluene deep oxidation than thermal catalysis. This work provides new insights for the design of high efficiency photothermal catalysis for the deep oxidation of VOCs.

Photocatalytic performance and mechanism insights of an S-scheme ZnMn2O4/ZIF-67 heterostructure in photocatalytic CO2 reduction under visible light irradiation

Improved separation among photoelectrons and holes (e−, h+) and regulated electron transport routes are essential to improve photocatalytic performance. This work adopts a convenient but more efficient method to prepare an S-scheme composite photocatalyst integrating narrow band gap semiconductor ZnMn2O4 (ZMO) and zeolitic imidazole framework ZIF-67(Z67) for improved photocatalytic CO2 reduction. The designed photocatalyst ZMO(X)/Z67 showed more visible light harvesting capacity compared to individual ZMO and Z67. The ZMO/Z67 nanocomposite containing 3 % ZMO nanosphere produced 1.91 times higher methanol (48.64 μmolg−1) compared to pure Z67 (25.36 μmolg−1) and 1.42 times higher ethanol (30.32 μmolg−1) compared to pure Z67 (21.28 μmolg−1) after 8 h visible light illumination. The composites' increased photocatalytic performance might be attributed primarily to excellent photogenerated charge separation and transfer via the linked S-scheme heterojunction between ZMO nanospheres and Z67. Various characterization methods are used to explore the structural, morphological, optical, and electrochemical features of produced photocatalysts, and a thorough photocatalytic mechanism is provided. After four recycling, the composite photocatalyst demonstrated good stability and recyclability. This study attributed to a viable method for constructing a direct S-scheme heterojunction for photocatalytic CO2 reduction.

Microstructure Strain of ZnMn2O4 Spinel by Regulation of Tetrahedral Sites for High‐Performance Aqueous Zinc‐Ion Battery

AbstractManganese oxides are widely used as cathode materials in aqueous zinc‐ion batteries (AZIBs) due to their low cost, multiple oxidation states, and high theoretical specific capacity. However, the further development of Mn‐based oxides is severely hindered by poor structural reversibility and sluggish reaction kinetics. Herein, a microstructure strain strategy is proposed to regulate the microstructure of MnO6 in ZnMn2O4 (ZMO) through partial atomic substitution on tetrahedral sites. The Ni substitution of ZMO (ZNxMO) with enlarged crystal plane spacing, increased Mn─O bond binding energy, and enhanced oxygen vacancy defects exhibits superior structural stability and faster ion transport kinetics. Correspondingly, the ZN0.5MO/NCNTs cathode delivers a favorable high specific capacity of 239.2 mAh g−1 at 0.1 A g−1 with excellent rate performance as well as longer‐term cycle life (over 3000 cycles at 1.0 A g−1). The outstanding performance of ZNxMO is deeply rooted in its Zn2+‐transport friendly in asymmetric MnO6 channel and the structure reversibility during the Zn2+‐intercalation/deintercalation process. This study provides an excellent example of using a microstructure strain strategy to design stable and high‐specific capacity manganese‐based cathode materials for Zn storage.

Charging behavior of ZnMn2O4 and LiMn2O4 in a zinc- and lithium-ion battery: an ab initio study

In the field of sustainable energy storage systems, zinc-ion batteries (ZIB) employing aqueous electrolytes have emerged as viable successors to the widely used lithium-ion batteries, attributed to their cost-effectiveness, environmental friendliness, and intrinsic safety features. Despite these advantages, the performance of ZIBs is significantly hindered by the scarcity of suitable cathode materials, positioning manganese zinc oxide (ZnMn2O4) as a potential solution. In this study, we describe the ZnMn2O4 (ZMO) compound focusing on its properties variations during Zn extraction and potential battery applications. For the sake of comparison, we also analyze the same properties of the LiMn2O4 in its tetragonal phase (TLMO), for the first time, motivated by a recent discovery that the substitution of Zn ions by Li in ZMO forms isostructural TLMO compound at room temperature. The study was conducted within the density functional theory (DFT) framework, where the structural, electronic, magnetic, electrochemical, and spectroscopic properties of ZMO and TLMO are investigated under various conditions. Although both systems crystallize in tetragonal structures, they demonstrate distinct electronic and magnetic properties due to different oxidation states of the Mn. Computationally optimized lattice parameters align closely with experimental values. The TLMO exhibits a narrower band gap compared to ZMO, indicating enhanced electrical conductivity. In addition, TLMO presented a lower diffusion energy barrier than ZMO, indicating better ionic conductivity. To evaluate the potential application of these materials in battery technologies, we further explored their volume changes during charging/discharging cycles, simulating Zn or Li ions extraction. TLMO underwent a significant volume contraction of 5.8% upon complete Li removal, while ZMO experienced a more pronounced contraction of 12.5% with full Zn removal. By adjusting ion extraction levels, it is possible to reduce these contractions, thereby approaching more viable battery applications. Voltage profiles, constructed from DFT-based simulation results, unveiled an average voltage of 4.05 V for TLMO, closely matching experimental values. Furthermore, spectroscopy results provide insights into the electronic transitions and validate the computational findings, consolidating our understanding of the intrinsic properties of ZMO and TLMO.

Spinel ZnMn2O4 nanosphere for the efficient Sulfamethazine degradation under visible light irradiation and photoelectrochemical study

This study assessed the efficacy of ZnMn2O4 (ZMO) spinel structure, synthesized via the solvothermal method, as a photocatalyst for the efficient photocatalytic degradation of Sulfamethazine (SMT) under visible light conditions. Comprehensive analyses involving FESEM, TEM, EDX, XRD, Raman, FTIR, XPS, and BET have been conducted, and the results strongly supported the successful preparation of ZMO. The optical characteristics of the as-synthesised sample was assessed using UV–VIS DRS, which indicated a band gap that was conducive to the effective absorption of visible light. Mott-Schottky (M-S) plot, Electrochemical Impedance Spectroscopy (EIS) analysis and photocurrent study have been utilised for knowing the type of semiconductor, kinetic charge transfer and charge separation and transfer within the on and off areas respectively. Degradation of SMT has been done in a suitable photochemical reactor and reaction rate constant has been evaluated. The study employed RSM modelling with Box-Behnken design to optimise various operational parameters in a photocatalytic reaction. These parameters included solution pH, dosage of ZMO, and initial concentration of SMT. Following a duration of 60 minutes under ideal circumstances, the residual concentration of SMZ declined to a level that is no longer detectable. The utilisation of tandem mass spectrometry has been employed to discover the transition products and their existence has been subsequently utilised to propose a degradation pathway.

Influence of Al Doping on the Structural, Optical, and Electrical Characteristics of ZnMn2O4

Doped zinc manganite samples were synthesized using the sol-gel method, incorporating varying amounts of aluminum (ZnMn2-xAlxO4, x = 0, 0.03, 0.05, 0.07, 0.1). High quality X-ray diffraction data enabled detection and accurate quantification of the predominant phase ZnMn2O4 (ZMO) and minor phase ZnO. The structure and microstructure of developed phases were investigated applying the Rietveld refinement method. The nanoscale nature of the samples was examined by High-resolution transmission electron microscopy (HRTEM); the incorporation of Al into the ZMO matrix and the oxidation states of various cations were studied through X-ray photoelectron spectroscopy (XPS). The introduction of Al has resulted in a modification of the light-absorption characteristics of the ZMO sample. Specifically, the direct optical band gap energy of ZMO decreased from 2.45 to 2.25 eV with an increase in the amount of Al doping to 0.1. Moreover, an investigation was conducted into the impact of Al doping amount, frequency, and temperature on the dielectric constant, dielectric tangent loss, ac conductivity, complex impedance, and complex electric modulus. It was observed that all samples, except for the sample with x = 0.05, exhibited ferroelectric features. The activation energies for the samples with x = 0, 0.03, 0.05, 0.07, and 0.1 were determined to be 0.274, 0.456, 0.099, 0.103, and 0.152 eV, respectively. The conduction mechanism type in the different samples was identified. The obtained changes of dielectric properties indicated the capability of improving the ZMO characteristics for various applications via controlling the doping content of Al.

Degradation of 2, 4-dichlorophenol by peroxymonosulfate catalyzed by ZnO/ZnMn2 O4.

In this study, a highly efficient peroxymonosulfate (PMS) activator, ZnO/ZnMn2 O4 , was synthesized using a simple one-step hydrothermal method. The resulting bimetallic oxide catalyst demonstrated a homogenous and high-purity composition, showcasing synergistic catalytic activity in activating PMS for degrading 2, 4-dichlorophenol (2, 4-DCP) in aqueous solution. This catalytic performance surpassed that of individual ZnO, Mn2 O3 , and ZnMn2 O4 metal materials. Under the optimized conditions, the removal efficiency of 2, 4-DCP reached approximately 86% within 60 min, and the catalytic ability remained almost constant even after four cycles of recycling. The developed degradation system proved effective in degrading other azo-dye pollutants. Certain inorganic anions such as HPO4 - , HCO3 - , and NO3 - significantly inhibited the degradation of 2, 4-DCP, while Cl- and SO4 2- did not exhibit such interference. Results from electrochemical experiments indicated that the electron transfer ability of ZnO/ZnMn2 O4 surpassed that of individual metals, and electron transfer occurred between ZnO/ZnMn2 O4 and the oxidant. The primary active radicals responsible for degrading 2, 4-DCP were identified as SO4 •- , OH• and O2 •- , generated through the oxidation and reduction of PMS catalyzed by Zn (II) and Mn (III). Furthermore, X-ray photoelectron spectroscopy (XPS) analysis of the fresh and used catalysts revealed that the exceptional electron transfer ability of ZnO facilitated the valence transfer of Mn (III) and the transfer of electrons to the catalyst's oxygen surface, thus enhancing the catalytic efficiency. The analysis of radicals and intermediates indicates that the two main pathways for degrading 2, 4-DCP involve hydroxylation and radical attack on its aromatic ring. PRACTITIONER POINTS: A bimetallic ZnO/ZnMn2 O4 catalyst was synthesized and characterized. ZnO/ZnMn2 O4 can synergistically activate PMS to degrade 2, 4-DCP compared with single metal oxide. Three primary active radicals, O2 •- , • OH, and SO4 •- , were generated to promote the degradation. ZnO promoted electron transfer among the three species of Mn to facilitate oxidizing pollutants. Hydroxylation and radical attack on the aromatic ring of 2, 4-DCP are the two degradation pathways.

The Promotion of Research Progress of Zinc Manganate Cathode Materials for Zinc-Ion Batteries by Characterization and Analysis Technology.

Zinc-ion batteries (ZIBs) have recently attracted great interest and are regarded as a promising energy storage device due to their low cost, environmental friendliness, and superior safety. However, the development of suitable Zn-ion intercalation cathode materials remains a great challenge, resulting in unsatisfactory ZIBs that cannot meet commercial demands. Considering that spinel-type LiMn2O4 has been shown to be a successful Li intercalation host, spinel-like ZnMn2O4 (ZMO) is expected to be a good candidate for ZIBs cathodes. This paper first introduces the zinc storage mechanism of ZMO and then reviews the promotion of research progress in improving the interlayer spacing, structural stability, and diffusivity of ZMO, including the introduction of different intercalated ions, introduction of defects, and design of different morphologies and in combination with other materials. The development status and future research directions of ZMO-based ZIBs characterization and analysis techniques are summarized.

Nanostructured ZnxMn3‒xO4 thin films by pulsed laser deposition: A spectroscopic and electrochemical study towards the application in aqueous Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) represent a safe and sustainable technology amongst the post-lithium systems, though the poor understanding of the material behaviour at the cathode prevents the full development of efficient AZIBs. ZnMn2O4 (ZMO) has been considered one of the cathode candidates owing to its analogy to the well-established LiMn2O4 cathode for lithium-ion batteries, however its electrochemical mechanism in the presence of Zn ions in aqueous environment is unclear and still debated. In this work, we synthesised nanostructured ZMO thin films by Pulsed Laser Deposition (PLD) and we evaluated, through extensive characterization by microscopic, spectroscopic, and diffraction techniques, how the deposition and annealing conditions affect the film properties. The self-supported nature and the high degree of control down to the nanoscale make a thin film an ideal model system to study the electrochemistry of the material in aqueous solution and to emphasize the impact of the film properties on its electrochemical response. We highlighted the crucial role of the oxygen pressure in the modulation of the film porosity and the combined effect of deposition pressure and annealing temperature to produce a film with tailored properties in terms of morphology, crystallinity, and Zn stoichiometry. A complex redox mechanism involving multiple concurrent reactions and the formation of zinc hydroxide sulphate hydrate (ZHS) was reported, as well as the influence of the film porosity on the voltammetric behaviour of the film at higher scan rate. Our results confirm the intricate electrochemical mechanism of the ZMO material, which does not merely involve the Zn2+ insertion/extraction but also the crucial participation of Mn2+ from the electrolyte, and pave the way for the nanoscale design of engineered ZMO-based electrodes.

Regulating the Electronic Configuration of Spinel Zinc Manganate Derived from Metal-Organic Frameworks: Controlled Synthesis and Application in Anode Materials for Lithium-Ion Batteries.

In recent years, transition metal oxides have been considered as the most promising anode materials due to their high theoretical capacity, low price, and abundant natural reserves. Among them, zinc manganate is used as an electrode material for anodes, whose application is mostly hindered due to its poor ionic/electronic conductivity. In this work, a series of ZnMn2O4 (ZMO) are synthesized by a hydrothermal technique coordinated with a metal-organic framework-based high-temperature calcination process for their application as an anode in lithium-ion batteries (LIBs). Meanwhile, this study systematically explores the influence of carbon doping and the types of organic ligands and oxygen vacancies on the electrochemical properties of the synthesized ZMO. Density functional theory (DFT) calculations and experimental investigations reveal that the introduction of carbon and oxygen vacancies can enhance electronic conductivity, more active sites and faster Li+ adsorption, resulting in better electrochemical performances. As expected, all ZMOs with carbon doping (PMA-ZMO, MI-ZMO, and BDC-ZMO) derived from 1,2,4,5-benzenetetracarboxylic acid, 2-methylimidazole, and 1,4-dicarboxybenzene achieve outstanding electrochemical performance. Meanwhile, the introduction of oxygen vacancies can enhance the electronic conductivity and can significantly reduce the activation energy of Li+ transport, thereby accelerating the Li+ diffusion kinetics in the lithiation/delithiation process. Furthermore, an optimal ZMO anode material synthesized by 2-methylimidazole delivers a high reversible capacity of 1174.7 mA h g-1 after 300 cycles at 0.1 A g-1 and 600 mA h g-1 at 0.5 A g-1 after 300 cycles. After high-rate charge and discharge cycles, the specific capacity rapidly recovers to a value greater than the initial value, which proves the unusual activation and thereby an excellent rate property of the electrode. Hence, we conclude that ZMO provides potential application prospects as an anode electrode material for LIBs.

Rational design of ZnMn2O4 nanoparticles on carbon nanotubes for high-rate and durable aqueous zinc-ion batteries

ZnMn2O4 (ZMO) is a promising cathode material for aqueous zinc-ion batteries (ZIBs) due toits high capacity, high output voltage and rich abundance. However, the commercial application of ZMO is severely restricted by the rapid capacity decay at high rate resulting from low electrical conductivity and structural degradation. Herein, a commonplace one-step hydrothermal method is applied to rationally synthesize ZMO nanoparticles (∼20 nm) on carbon nanotubes (ZMO/CNTs) heterostructure for stable high-rate Zn2+ storage. The high electrical conductive CNTs and such small ZMO benefit from electrons’ fast transport, endowing ZMO/CNTs composite with high electrical conductivity. Furthermore, the flexible CNTs network and the strong interface interaction (Mn-O-C bond) between ZMO and CNTs can effectively suppress irreversible structural degradation. As a result, the ZMO/CNTs composite delivers a promising initial capacity of 220.3 mAh g−1 at 100 mA g−1 and a high capacity retention of 97.01% after 2000 cycles at 3000 mA g−1, indicating excellent high-rate long-term cycling stability. Furthermore, the flexible ZIBs are assembled and show stable electrochemical properties at different bending states, demonstrating their potential practical applications.

A Valence-Engineered Self-Cascading Antioxidant Nanozyme for the Therapy of Inflammatory Bowel Disease.

Antioxidant treatment strategy by scavenging reactive oxygen species (ROS) is a highly effective disease treatment option. Nanozymes with multiple antioxidant activities can cope with the diverse ROS environment. However, lack of design strategies and limitation of negative correlation for nanozymes with multiple antioxidant activities hindered their development. To overcome these difficulties, here we used ZnMn2 O4 as a model to explore the role of Mn valency at the octahedral site via a valence-engineered strategy, and found that its multiple antioxidant activities are positively correlated with the content of Mn4+ . Therefore, through this strategy, a self-cascading antioxidant nanozyme LiMn2 O4 was constructed, and its efficacy was verified at the cellular level and in an inflammatory bowel disease model. This work not only provides guidance for the design of multiple antioxidant nanozymes, but also broadens the biomedical application potential of multiple antioxidant nanozymes.

Coprecipitation mechanisms of Zn by birnessite formation and its mineralogy under neutral pH conditions

Birnessite (δ-Mn(IV)O2) is a great manganese (Mn) adsorbent for dissolved divalent metals. In this study, we investigated the coprecipitation mechanism of δ-MnO2 in the presence of Zn(II) and an oxidizing agent (sodium hypochlorite) under two neutral pH values (6.0 and 7.5). The mineralogical characteristics and Zn–Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis. Batch coprecipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0, which was similar to the result of adsorption experiments at pH 6.0 and 7.5. X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism on δ-MnO2 under these experimental conditions. A coprecipitation experiment at pH 6.0 produced some hetaerolite (ZnMn(III)2O4) and manganite (γ-Mn(III)OOH), but only at low Zn/Mn molar ratios (< 1). These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable. Woodruffite (ZnMn(IV)3O7•2H2O) was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5. This resulted in a Brunauer–Emmett–Teller (BET)-type sorption isotherm, in which formation was explained by transformation of the crystalline structure of δ-MnO2 to a tunnel structure. Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn–Mn compound formation on the δ-MnO2 surface, and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.

Rational Design of ZnMn2O4 Quantum Dots in a Carbon Framework for Durable Aqueous Zinc‐Ion Batteries

Manganese oxides are promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high energy density and low cost. However, in their discharging processes, the Jahn-Teller effect and Mn3+ disproportionation often lead to irreversible structural transformation and Mn2+ dissolution, deteriorating the cycling stability of ZIBs. Herein, ZnMn2 O4 quantum dots (ZMO QDs) were introduced into a porous carbon framework by in-situ electrochemically inducing Mn-MIL-100-derived Mn3 O4 quantum dots and the carbon composite. In such ZMO QDs and carbon composite, the quantum dot structure endows ZnMn2 O4 with a shorter ion diffusion route and more active sites for Zn2+ . The conductive carbon framework is beneficial to the fast transport of electrons. Furthermore, at the interface between the ZMO QDs and the carbon matrix, the Mn-O-C bonds are formed. They can effectively suppress the Jahn-Teller effect and manganese dissolution of discharge products. Therefore, Zn/ZMO QD@C batteries display remarkably enhanced electrochemical performance.

Rationally Designed Mn2 O3 -ZnMn2 O4 Hollow Heterostructures from Metal-Organic Frameworks for Stable Zn-Ion Storage.

Mn-based oxides have sparked extensive scientific interest for aqueous Zn-ion batteries due to the rich abundance, plentiful oxidation states, and high output voltage. However, the further development of Mn-based oxides is severely hindered by the rapid capacity decay during cycling. Herein, a two-step metal-organic framework (MOF)-engaged templating strategy has been developed to rationally synthesize heterostructured Mn2 O3 -ZnMn2 O4 hollow octahedrons (MO-ZMO HOs) for stable zinc ion storage. The distinctive composition and hollow heterostructure endow MO-ZMO HOs with abundant active sites, enhanced electric conductivity, and superior structural stability. By virtue of these advantages, the MO-ZMO HOs electrode shows high reversible capacity, impressive rate performance, and outstanding electrochemical stability. Furthermore, ex situ characterizations reveal that the charge storage of MO-ZMO HOs mainly originates from the highly reversible Zn2+ insertion/extraction reactions.

Changes in optical properties and structural phases grown upon forming ZnMn2O4/ZnFe2O4 heterostructure nanocomposite

The heterostructure nanocomposites (1-x)ZnMn2O4/xZnFe2O4 (x = 0, 0.2, 0.5, 0.8, 1) are formed using the co-precipitation technique. X-ray diffraction and Fourier-transform infrared spectroscopy data disclosed the dissolving of some ions of one phase into the matrix of the other phase. Composite samples with x = 0.5 and 0.8 have an extra ZnO phase and its percentage increased with increased ZnFe2O4 (ZFO) amount in the matrix. The elements constituting the samples and the cations valence state are determined by X-ray photoelectron spectroscopy technique (XPS). The effect of composition parameter (x) on the absorbance spectra, extinction coefficient, refractive index, dielectric constant (real and imaginary), dielectric loss and optical conductivity is investigated by UV diffused reflectance technique. The optical band gap (Eg) of (1-x)ZMO/xZFO (x = 0.2, 0.5) nanocomposite samples was decreased to 2.4, 2.38 while the Eg of nanocomposite sample with x = 0.8 was increased to 2.54 eV. All nanocomposite samples have a normal dispersion similar to ZnMn2O4 (ZMO) sample. ZFO sample exhibited both normal and anomalous dispersion depended on the wavelength range. The 0.2ZMO/0.8ZFO nanocomposite sample exhibited a good nonlinear optical behavior at low frequency. The photoluminescence (PL) intensities of nanocomposite samples are quenched as ZMO alloyed with ZFO. Different emitted colors are observed as the ratio of ZMO and ZFO altered in the matrix.

Spinel oxide incorporated photoanode for better power conversion efficiency in dye-sensitized solar cells

In this study, ZnMn2O4 (ZMO) nanoparticles were synthesized and mixed with the commercial TiO2 to prepare composite photoanode. Dye sensitized solar cells (DSSC) device was fabricated and highest power conversion efficiency of 5.09% was obtained for the cell with 0.1 wt% of ZMO in the photoanode, while in similar condition the device with pure TiO2 photoanode showed power conversion efficiency of 4.124%. This improvement in the power conversion efficiency of the composite photoanode based cell was attributed to the presence of critical amount of ZMO which synergistically improve the light absorption, charge transport properties prevented charge recombination, eventually it improved open-circuit voltage (Voc) and short-circuit current (Isc).