Manganese Oxide Phases Research Articles

Morphologically tuned MnO2 thin film electrodes prepared by growth kinetic dependent SILAR approach for high-performance extrinsic pseudocapacitors

Rationally designed electrode materials that are morphologically tuned to attain large surface area can significantly possess the extrinsic pseudocapacitive charge-storing ability. Therefore, the current work approach focuses on synthesizing binder-free MnO2 thin film electrodes with tuned morphology by the SILAR method through alteration in growth kinetics. The growth kinetics of SILAR are controlled by altering the precursor concentrations ratio among metal precursor (MnCl2) and oxidizing agent (KMnO4). The structural analysis confirmed the preparation of the δ-MnO2 phase of manganese oxide. Moreover, alteration in growth kinetics resulted in a change in surface morphology with reduced nanowire size of marigold-like δ-MnO2 microflowers. The MO-3 thin film electrode prepared at an optimum KMnO4 and MnCl2 precursor concentration ratio of 2:1 provides the maximum extrinsic pseudocapacitive conduct with the maximum specific capacitance of 774.5 F g−1. Furthermore, the aqueous symmetric supercapacitor device exhibits the highest specific capacitance of 106 F g−1 with a specific energy of 14.8 Wh kg−1 at a high specific power of 1792 W kg−1 and exhibits 83.2 % capacitive retention over 10,000 cycles. Furthermore, the symmetric aqueous device (MO-3//Na2SO4//MO-3) lights 5 red LEDs, demonstrating its commercial viability for energy storage systems. This research facilitated the scalable synthesis of binder-free δ-MnO2 fine film electrodes with a desired morphology by facile SILAR method, ensuring their practical applicability in symmetric extrinsic pseudocapacitor devices.

Unlocking enhanced new type of safe open system lithium-ion battery performance: Mn3O4 nano-cubes and their sulfur mixers cathode material

In the pursuit of advancing lithium-ion (Li-ion) battery technology towards enhanced safety and performance, we present research study on the synthesis and evaluation of manganese oxide-based cathode materials. Different phases of manganese oxides (Mn3O4 and MnO2), alongside their different ratio of two manganese oxides phases and Mn3O4 with sulfur (S) combination, we employed a simple hydrothermal and solid-state grinding techniques. Characterized by field emission transmission electron microscopy (FE-TEM), our synthesized materials revealed distinct phases of MnO2 and Mn3O4 accompanied by nanorods (NRs) and nanocubes (NCs) morphologies, respectively. We conducted a comprehensive assessment of the Li-ion battery performance of these materials, initially without S, within a new type of safe open system framework. Notably, Mn3O4 NCs (MNCs) developed as important, exhibiting a maximum discharge capacity of 346.03 mAh/g at a constant current discharging rate of 0.5 A/g. We introduced 30 % of S into 70 % of the MNCs matrix to form the MNCSs-73 composite, resulting in rather moderate enhancement in capacity performance. The MNCSs-73 displayed an exposed discharge capacity of approximately 394.8 mAh/g under identical testing conditions. Our findings underscore the exceptional potential of MNCs and MNCSs-73 composites cathode materials for highly suitable for open system novel safe Li-ion battery applications and other energy storage research field.

Synthesis and phase transformation study of nanostructured manganese oxide polymorphs

This paper presents the green synthesis of manganese oxide nanoparticles using olive leaf extract (OLE). The extract functions as both a reducing agent, responsible for converting manganese ions into nanoparticles, and a capping agent, aiding in stabilizing the formed nanoparticles. Our focus lies on investigating the thermal stability, phase transformation, and decomposition temperatures of different manganese oxide phases in powder form as a function of the calcination temperature. Since phase transformation depends on temperatures change at the nanoscale both thermogravimetric and differential scanning calorimetry (TGA, DSC) are used to determine the new phase transformation temperatures of the synthesized nanoparticles. Moreover, the phase structure and the exact stoichiometry are studied using ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning/transmission electron microscopy (SEM/TEM). XRD and XPS analyses reveal the formation of amorphous MnOx at room temperature (prior to calcination), transitioning to crystalline phases (Mn2O3 and Mn3O4) post-calcination. High-resolution TEM and SEM depict the formation of nanoparticles around 15 nm in size, exhibiting different shapes. BET technique calculations give a very high specific surface area, rending these nanoparticles excellent candidates for several applications.

Elucidating the Role of Copper-Induced Mixed Phases on the Electrochemical Performance of Mn-Based Thin-Film Electrodes.

Manganese oxide is a fascinating material for use as a thin-film electrode in supercapacitors. Herein, the consequences of copper incorporation on spray pyrolyzed manganese oxide thin films and their electrochemical performance were investigated. The Cu-incorporated manganese oxide thin films were deposited by spray pyrolysis, and their structural and electrochemical properties were thoroughly evaluated. The formation of the spinel Mn3O4 phase with effective Cu incorporation was confirmed by X-ray diffraction investigation. Through Raman studies, it was noticed that mixed phases of manganese oxide tend to form after Cu incorporation, and this result was also reflected in X-ray photoelectron spectroscopic studies. The surface morphology and roughness were also altered by the addition of copper. However, electrochemical measurements implied a reduction in the specific capacitance upon copper inclusion. The cyclic voltammetry test indicated a specific capacitance of 132 F/g for Mn3O4 electrodes, but a substantial drop for copper-incorporated samples due to the mixed manganese phase. The decremental tendency was further supported by galvanostatic charge-discharge studies and electrochemical impedance spectroscopic measurements. These results provide valuable insights into the effects of copper addition in manganese oxide thin-film-based electrodes for energy storage applications.

Lessons Using an Electrochemical Method to Produce Lithium Manganese Oxide Cathodes for Lithium-Ion Batteries

Lithium manganese oxide (LMO) has been a well-studied Li-ion battery cathode material for for many years. It offers high thermal stability for high-temperature battery applications and a prolonged cycle life compared to other materials. LMO also has an acceptably high energy density from a naturally abundant, inexpensive, and environmentally benign material, i.e. manganese (Mn). The cathodes for LIBs are conventionally synthesized via solid-state reaction techniques, which require harsh and complex conditions including high temperature (> 700oC) and high pressure. The resulting powders are incorporated into a slurry that is cast onto a current collector using a binder, additives, and solvent. Though this results in high-performing electrodes, it also usually increases the production cost. Another approach that is gaining traction to make LMOs is electrodeposition. Electrodeposition can allow for the direct synthesis of the active material on the current collector without using any binder or additives. Using electrodeposition not only could eliminate the mass and volume of inactive material but also reduce the cost of electrode fabrication. It also can facilitate recycling by depositing the active material from lower purity, material-digested streams.A few reports in the literature have discussed the electrochemical preparation of LMO cathode from the following steps: electrodeposition of manganese oxide (s) (MnxOy) onto a substrate followed by chemical lithiation and heat treatment of MnxOy [1,2]. Although a few reports showed the active materials with reasonable capacity, it is presently unknown what LiMnxOy phase or phases are active and which MnxOy is responsible. However, without sufficient physicochemical investigation, multiple works have postulated that the LMO is created from crystalline MnO2 or Mn3O4. It is also not known what the typical active phase yield is or what physical structures or conditions are responsible for increased capacity. If electrodeposition-to-LMO is to become a viable commercial pathway, a rational understanding of the solid-state chemistry for the LMO formation is needed.This talk will discuss the deposition and lithiation of multiple manganese oxide phases – linking the chemistry and morphology of the surface features to their charge/discharge properties. It will be shown that traditional crystalline phases are not responsible for the formation of LMOs. It will also be shown that the LMOs do not fully delithiate during charging. Lastly, the precise morphology of the active phase – separated out through new processing approaches – will be identified. The composition, structure, and crystallinity of the Mn oxides and LMOs were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The resulting LMO electrodes were incorporated into coin cells, cycled – achieving a capacity of 261 mAh g-1, and post-characterized.References J. Rana, M. Stan, R. Kloepsch, J. Li, G. Schumacher, E. Welter, I. Zizak, J. Banhart, and M. Winter, Adv. Energy Mater., 4, 1300998 (2014).Z. Quan, S. Ohguchi, M. Kawase, H. Tanimura, and N. Sonoyama, J. Power Sources, 244, 375 (2013).

High photocatalytic activity and stability of MnV2O6 and Mn2V2O7 synthesized by simple low temperature method for bromophenol blue degradation

Developing an efficient catalyst for Bromophenol blue dye is of great importance for the degradation and mineralization of organic pollutants. Herein, in this study, a hydrothermal approach was used to prepare two different phases of manganese and vanadium mixed oxides, MnV2O6 and Mn2V2O7, and they were used as photocatalysts under visible light. To confirm the structural and morphological properties of MnV2O6 and Mn2V2O7 materials, XRD, SEM-EDS, ICP, BET, XPS, and UV–vis (DRS) were used. The linear fit plot for MnV2O6 and Mn2V2O7 indicates a band gap energy of 1.96 eV and 1.82 eV, respectively. The results revealed that Mn2V2O7 has better photocatalytic performance in bromophenol blue (BPB) degradation than MnV2O6: in 120 min, the BPB exhibits a degradation efficiency of 99.88% for Mn2V2O7 and 96.58% for MnV2O6, and COD was reduced from 41.2 mg/L to 1.37 mg/L for Mn2V2O7 and 4.21 mg/L for MnV2O6, confirming the substantial mineralization of BPB. The Mn2V2O7 preparation method improved its absorption in the visible region, which avoided the rapid charge recombination, and enhanced the electron transfer, resulting in the enhancement of its photocatalytic performance. Furthermore, free radical scavenging tests were carried out and showed that superoxide ions and hydroxyl radicals are responsible for the BPB dye conversion. Finally, this research illustrates a novel insight into designing two different phases of manganese and vanadium mixed oxides, with photocatalytic ability for wastewater treatment.

Electrodeposition of Manganese-Based Cathode Materials for Lithium-Ion Batteries

To reduce the cost of electrode fabrication and provide a pathway for facile recycling of battery active materials, electrochemical deposition and lithiation of manganese (Mn) oxide cathodes have been proposed in the literature. However, without sufficient physicochemical characterization, many works have postulated that the active lithium manganese oxide (LMO) phase is created from crystalline MnO2 or Mn3O4. This work shows that neither of those phases nor other well-known stoichiometric crystalline phases (i.e., MnO and Mn2O3), lead to the formation of LMO. This work confirms the specific active surface features obtained by the potentiostatic deposition of Mn oxide, their chemical lithiation, and heat treatment. The resulting LMO electrodes were incorporated into coin cells, cycled—achieving a capacity over 250 mAh g−1—and post-characterized.

Identification of tunnel structures in manganese oxide minerals using micro‐Raman spectroscopy

AbstractManganese oxides have attracted the interest of many researchers due to their broad application field. These oxides possess various electrochemical, adsorption and catalysis properties and are as such applied in the industrial context, for example, steel industry, catalysis and removal of toxins in the ground or in waste water. In the archaeometrical field, manganese oxides have been used as pigments on various artefacts such as pottery and rock art paintings. The diversity of manganese oxide applications highlights the need for a well‐defined Raman spectroscopic database with correct characterization of these compounds. However, identification of manganese oxides by Raman spectroscopy is challenging due to the wide variety of manganese oxides, and manganese oxides are weak Raman scatterers and are susceptible under the laser light. As such, characterization by Raman spectroscopy is not straight forward. In this research, we have focussed on seven natural, mineral (tunnel) samples that were identified by micro‐Raman spectroscopy using two different laser wavelengths (785 and 532 nm). The experimental conditions were controlled to not introduce any modifications (degradation and/or phase transition) of the manganese oxide species. Both lasers have proven to be successful and were able to retrieve well‐characterized Raman spectra for each of the manganese oxide phase, which were compared with published literature.

Complete removal of CO at ambient conditions using copper manganese oxide (CuMnOx) catalysts synthesised via co-precipitation with ultrasonic irradiation

This present work investigates the novel method of synthesising copper manganese oxide (Hopcalite) catalysts with a Cu:Mn ratio of 1:2 by using a facile ultrasound-assisted co-precipitation synthesis technique. The CuMnOx catalysts were synthesised using an ultrasonic bath or an ultrasonic probe with varying ultrasonic powers. The catalysts were further characterised and evaluated for the oxidation of carbon monoxide (CO). Characterisation results revealed that samples prepared using the ultrasonic method exhibited enhanced physical properties, such as highly dispersed particles with a larger surface area and pore size. Besides, the presence of mixed copper and manganese oxide phases was detected, which provided synergistic interactions to facilitate and enhance CO oxidation. The amorphicity and reducibility of the catalysts were also improved, thus indicating the presence of more active sites. Furthermore, the catalyst prepared using the ultrasonic probe at a power of 23.3 W with a 15 min sonication time was found to be the most active, with the capability of oxidising CO to CO2 to completion (100 %) at ambient conditions. It also possessed high catalytic stability, in which catalytic activity was not compromised for as long as 200 min. On the whole, this work has ascertained that by incorporating a simple ultrasonic irradiation step into the synthesis procedure of copper manganese oxide catalysts, the overall performance of the catalyst can be greatly improved compared to those already found in the literature, which demonstrates the potential application of this new method on a wider, commercial scale for carbon monoxide removal.

Structure and properties of ion-plasma deposited films of CoCrFeMiMn high-entropy alloy

High-entropy Co19Cr18Fe22Mn21Ni20 thin films were obtained by the modernized method of three-electrode ion-plasma sputtering of mosaic targets consisting of pure metals. The structure, electrical resistance, and magnetic properties of films were investigated. Single diffuse halo was seen on the XRD patterns of the as-deposited films, which confirms their amorphous structure. Some of the thin films, which were annealed at 900 K in a vacuum, were identified to be oxidized by a small amount of oxygen in the work chamber. After the heat treatment, the Co19Cr18Fe22Mn21Ni20 films were transformed from an amorphous state into a crystallized FCC solid solution with the lattice parameter a=0.3613 nm. Also, the cubic B2 phase of FeCo with a lattice parameter of 0.2857 nm was formed in the annealed films. As a result of oxidation processes, a dispersed phase of manganese oxide also arose after annealing. The temperature dependencies of electrical resistivity of films were measured by the four-point technique upon continuously heating in the high vacuum. Both as-deposited and annealed films clearly revealed a typical ferromagnetic behavior. The as-deposited high-entropy film exhibited the soft magnetic properties while the annealed films could be attributed to hard magnetic materials.

Structure, Seebeck coefficient and DC electrical conductivity of Bi2Mn4O10 prepared by mechanochemical method

Bismuth and manganese oxides were mixed as source-materials using the mechanochemical technique followed by heat treatment to prepare the phase Bi2Mn4O10. The X-Ray Diffraction (XRD) analysis was carried out to obtain the formed phases during the mechanochemical process. Bismuth manganese oxide phase with the chemical formula Bi2Mn4O10 was formed at heat treatment 1073 K and was partially decomposed to γ-Bi12.8O19.2 and α-Mn2O3 after 5 h of milling time. The variation of the crystallite size is obtained at different milling time (1 h, 5 h, 10 h, 15 h, 30 h and 50 h). The temperature dependency of the DC electrical conductivity was observed at different milling times in the temperature range 300–425 K for the samples milled at 5 h, 10 h, 30 h and 50 h. The temperature dependency (300–4 80 K) of the thermoelectric power/Seebeck coefficient (S) and its modulus variation with milling time were observed; the modulus varied in the range (45 µV/K-277 µV/K). The concentration of manganese ions (N), the average distance between manganese ions (R) and the fraction (C) of reduced transition ions were calculated for all samples. The hopping carrier mobility (μ) of the samples was also calculated at a fixed temperature. As a result, the conduction mechanism agreed with the non-adiabatic process of small polaron hopping.

Structure and Performance of NaxMn0.85Al0.1Fe0.05O2 (0.7 ≤ x ≤ 1.0) Composite Materials for Sodium-Ion Batteries.

P2 and O3 structures are two important sodium manganese oxide phases for sodium-ion batteries; however, encounter Na-deficient and poor rate performance, respectively. Herein, a systematic study of NaxMn0.85Al0.1Fe0.05O2 (0.7 ≤ x ≤ 1.0) materials is performed by employing solid-state NMR, X-ray diffraction, and electrochemical analysis, to provide an in-depth understanding on the structure and the correlated performance for the rational design. The interlayer spacing of α-NaMnO2 broadens, and the content of distorted O3 structures (α- and β-NaMnO2) increases with raising Na content. It is exhibited that the NaMn0.85Al0.1Fe0.05O2 composite material presents better rate and cycling performance than P2-type Na0.7Mn0.85Al0.1Fe0.05O2, delivering a capacity of 87 mAh g-1 at 5 C. Significantly, the determinants of performance are further discussed, which reveal that diffusion coefficient is probably not the decisive factor restricts the rate performance of O3 and composite materials. The phase transition relaxation and the interfacial charge transfer resistance should be seriously addressed for further improvement.

Metastable states and physical properties of Co-Cr-Fe-Mn-Ni high-entropy alloy thin films

In this study, Co19Cr18Fe22Mn21Ni20 HEA thin films have been obtained by the modernized method of three-electrode ion-plasma sputtering of mosaic targets consisting of pure metals. The structure, electrical resistance and magnetic properties of films were investigated. Single diffuse halo is observed on the XRD patterns of the as-deposited films, which confirms their amorphous structure. Some of the thin films, which were annealed at 900 K in a vacuum were identified to be oxidized by the small amount of oxygen in the work chamber. After the heat treatment, the Co19Cr18Fe22Mn21Ni20 films are transformed from an amorphous state into a crystallized FCC solid solution with the lattice parameter a = 0.3613 nm. Also, the cubic B2 phase of FeCo with a lattice parameter of 0.2857 nm is formed in the annealed films. As a result of oxidation processes, a dispersed phase of manganese oxide is also arising after annealing. Calculation of the activation energy of the beginning of phase transition was carried out by the generalized Kissinger method. The temperature dependencies of electrical resistivity of films were measured by the four-point technique upon continuously heating in the high vacuum. Both as-deposited and annealed films clearly reveal a typical ferromagnetic behavior. The as-deposited HEA film exhibits the soft magnetic properties while the annealed films can be attributed to hard magnetic materials.

Structure and optical properties of spray deposited Cu–Mn–O thin films for optoelectronic devices

Nanostructured copper manganese oxide (CMO) thin films were prepared by sol-gel method and deposited on glass substrate by spray pyrolysis technique. Different Cu acetate/Mn acetate molar ratios were used to study the effect of Cu acetate on the structure, morphological and optical properties of the deposited films. The prepared films were annealed at 500 °C in air. A polycrystalline structure and mixed oxide phases of copper manganese oxide were confirmed by X-ray diffraction, (XRD). High resolution transmission electron microscopy, (HRTEM), reveals homogenous and very fine grainy structures of the prepared films with a particle size range from 0.5 nm to 2 nm. The optical measurements showed that 93% is maximum optical transmission and the optical band gap of the prepared films was found to be influenced by increasing Cu acetate ratios from 40% to 60% indicating a blue shift. The energy band gap correlated with the allowed direct transition is found to increase from 3.21 eV to 3.58 eV with increasing Cu acetate while the refractive index decreases. The optical investigation by ultraviolet, visible light, and near-infrared, (UV–VIS–NIR), showed a clear absorption peak at 4.28 eV which attributed to the excitonic nature.

Experimental Comparison of Hydrogen Peroxide Catalysts for a Hydrogen -Decane Bipropellant Combustor

This paper presents an experimental comparison of the catalytic activity of different alumina-based catalysts for highly concentrated hydrogen peroxide (85% w.) decomposition. Three pellet-shaped catalysts with manganese oxide or platinum active phases were considered. Their performances were investigated by measuring the temperature increase in the catalytic bed after several injections of of hydrogen peroxide in a constant-volume chamber. This setup evidenced a loss of reactivity after several injections, which was due to water poisoning. Pellets were, then, tested in a small-scale catalytic chamber plugged into a combustor. Hydrogen peroxide was injected at various mass flow rates (from 4.5 to ) through the catalytic chamber. The temperature evolution at the exhaust was recorded via a thin thermocouple (1 mm) and used to compare the activity of the different catalysts. The specific surface area, the active phase amount, and the platinum dispersion were measured after the tests. Catalysts experienced a decrease of those values, evidencing the ageing of the catalytic material. Preliminary combustion tests were performed for all catalysts in a hydrogen bipropellant combustor. Results were compared to evaluate the influence of the efficiency of the catalytic system on combustion performance.

The Effect of Hydrogen Peroxide on Catalytic Activity of Manganosite MnO/Oil Palm Fly Ash Catalyst for Degradation Methylene Blue

Dye pollutions have become a major environmental problem due their mutagenic, carcinogenic nature, toxicity and stability. The effective removal of this recalcitrant material from wastewater requires immediate solution. The Fenton-based advanced oxidation processes have been considered as highly effective and efficient method for the degradation of highly stable organic contaminants. In this work, the composite MnO/oil palm fly ash (OPFA) was first synthesized, characterized and applied as a heterogeneous Fenton catalyst for the degradation of methylene blue (MB). The composite was characterized by X-ray powder diffraction (XRD), and Brunauer–Emmett–Teller (BET). The XRD result indicated that the manganese oxide phase in the composite is the rock-salt manganese oxide of manganosite MnO. The MnO/OPFA has a surface area of 278.541 m2/g, which is much higher than those of pure manganosite or OPFA. The catalytic test indicated that the concentration of hydrogen peroxide (H2O2) seems to play a significant role for the effective degradation of MB. The degradation of MB was 95.31 achieved only within 10 minutes of reaction time with the addition of 5 ml of H2O2, 125 mg catalyst using 100 ml 12.5 ppm MB.

Influencing Parameters for degradation of Methylene Blue using the catalyst bentonite supported manganosite MnO synthesized via facile, one-pot Sol-Gel Route

Textile industries consume considerable amounts of water in dyeing process, thus generating the enormous quantities of wastewater. The wastewater is a highly harmful to environment if discharged untreated or partially treated since it contains wide range of hazardous compounds and is also very difficult to treat. The structure of dye residues in wastewater is mostly complex polymeric structures, which is highly resistant to bio-degradation. The Fenton-based advanced oxidation process (AOP) was widely studied to treat recalcitrant organic contaminant and based on the production of OH following H2O2 activation by a catalyst. Manganese oxides are reported to be an active catalyst for degradation of a dye via Fenton process. Herein, bentonite supported MnO (MnO/bentonite) was synthesized via one-pot sol-gel synthesis and its catalytic activity was evaluated for the degradation of methylene blue (MB) using Fenton process. The X-ray diffraction results revealed the formation of the rock–salt MnO manganosite as crystalline phase of manganese oxide. The MnO/bentonite composite displayed higher performance for the degradation of MB than pure MnO. The maximum degradation of MB by MnO/bentonite composite was achieved by evaluating the process variables and compared to MnO (manganosite) as a control. In the optimum condition, the MnO/bentonite composite was able to degrade 92.97 % MB using 15 ml H2O2, 50 mg of catalyst and 25 ml MB (75 ppm) in 100 mL solution of initial MB concentration. Both catalyst concentration and H2O2 concentration seem to play a significant role for the degradation of MB using the composite MnO/bentonite.

The impact of Yb substitution on enhancing the thermoelectric properties of CuMnO2 nanostructures

In the present work, CuMn1-xYbxO2 nanostructure with various x values (x ​= ​0, 0.05, 0.1, 0.2) were prepared by high energy ball milling. The structural and morphological properties of the prepared samples were studied by XRD and SEM, analyses. XRD analysis confirms that a pure phase of copper manganese oxide (CuMnO2) was formed till x ​= ​0.05 and the secondary phase of Yb2O3 was observed while increasing the Yb concentration (x ​≥ ​0.1). The SEM images show nano rod-like morphology till x ​= ​0.1 and nanorods were agglomerated in the samples with higher values (x ​> ​0.1). The electrical resistivity and Seebeck coefficient of CuMn1-xYbxO2 (0 ≤ x ​≤ ​0.2) samples were measured at various temperatures. The electrical resistivity of the samples decreased till x ​≤ ​0.1 due to the complete dissolution of Yb ions in CuMnO2 lattice and the resistivity increases at higher Yb substitution (x ​> ​0.2) due to the secondary phase of Yb2O3. The Seebeck coefficient value decreased at x ​= ​0.1 and it increases at a higher x value of 0.2. CuMn0.09Yb0.05O2 shows a higher power factor of 0.0013 ​mW. K−2 m−1 at 575 ​K and low thermal conductivity of 3.2 ​W/m K at 668 ​K which are higher than pure samples. The experimental results show that Yb substitution has an enhanced effect on improving the thermoelectric properties of CuMnO2 nanostructure. The result reveals that the 0.05 ​Yb substituted sample shows a higher figure of merit (ZT) of 2.5x10−4 at 668 ​K.

Ag-doped manganese oxide catalyst for gasoline particulate filters: Effect of crystal phase on soot oxidation activity

Manganese oxide catalysts were synthesized by a hydrothermal method, and silver was doped to promote active oxygen generation. As the calcination temperature increased, the crystal phases of manganese oxide were changed into Mn2O3 from cryptomelane (KMn8O16). In the soot oxidation experiments under GPF conditions, Mn2O3 exhibited higher soot oxidation activities than cryptomelane. To identify the reason for soot oxidation activities, general characterization methods related to the redox properties of the catalyst were performed, including XPS, O2-TPD, H2 TPR, and Soot TPR. However, the soot oxidation activities were not correlated with the characterization results because cryptomelane had higher reducibility compared to Mn2O3. Therefore, cycled H2-TPR, which reflects the redox mechanism of the catalyst in the oxidation reaction, was performed. As a result, Mn2O3 readily regenerated active oxygen compared with cryptomelane, which resulted in higher soot oxidation activity under GPF conditions. In this study, the main factor in the soot oxidation activity of manganese oxide was unveiled, and the result is believed to be helpful in further study of soot oxidation using manganese oxide catalysts.

Conductive polymer composites cathodes for rechargeable aqueous Zn-ion batteries: A mini-review

With the supply of lithium resources beginning to dwindle, rechargeable aqueous zinc-ion batteries (AZIBs) have attracted research interests as alternatives to lithium-ion batteries. Developing high-performance and cost-effective cathodes can promote the commercialisation process of AZIBs. Transition metal-based materials, including different phases of vanadium oxides, manganese oxides and Prussian blue analogues are promising candidates due to their reasonable crystal structures to host Zn-ions. However, they are suffering from the low electrical conductivity and structural instability. The modification of these materials by conductive polymers and the formation of composites are demonstrated as promising strategies to solve the problem and improve the cathode performance in AZIBs. In this mini review, we summarize representative advancements of conductive polymer composites as cathodes in AZIBs and provide an insight into their future research directions.