Metal Manganese Oxides Research Articles

Green synthesis of [formula omitted]2[formula omitted]4[formula omitted] nanoparticles as effective electrode materials for electrochemical hydrogen and energy storage: A comparative study

Molecular hydrogen is a promising energy carrier and the best potential alternative for environment-damaging fossil fuels. Hydrogen as a secondary clean energy can lead to the development of fuel cell technology. Hydrogen transportation is highly costly due to its low volumetric energy density at ambient temperature and pressure. However, reactive hydrogen can be electrochemically generated in the solid state and occurs either as a surface-adsorbed or lattice-settled species. Herein, the mesoporous structures of LiMn2O4 and NiMn2O4 were prepared by using Aleo Vera extract as a complexing agent. The samples were characterized by various techniques to determine their crystal structures, surface morphology, and porosity. Electrochemical hydrogen storage abilities and the specific capacitance values of as-prepared mixed metal manganese oxides were measured in the 2 M KOH electrolyte solution. The results showed that LiMn2O4 and NiMn2O4 nanoparticles have an excellent specific capacitance of 783 and 552 Fg-1, respectively. The maximum discharge capacities of LiMn2O4 and NiMn2O4 nanoparticles were obtained to be 3605 and 1501 mAh/g after 11 cycles, respectively. The higher and excellent discharge capacity of LiMn2O4 can partially be ascribed to its higher porosity.

Construction of transition metal/metal oxide synergistic with carbon nanomaterials trinity composites to promote electrocatalytic oxygen evolution

Novel non-precious metal electrocatalysts replace precious metal catalysts for water separation and are highly anticipated in commercial applications. The coexistence of crystalline and amorphous phases is thought to facilitate efficient electrocatalytic activity. In this work, a facile strategy is proposed to induce crystalline-amorphous core-shell nanocomposites via direct-current (DC) arc plasma technology. Heterogeneous crystalline amorphous nanocomposites (Fe/MnO@C) formed by coupling transition metal manganese oxide and magnetic iron into a carbon matrix exhibit excellent water oxidation properties. Spin-pinning effect is formed at the ferromagnetic metal/antiferromagnetic manganese oxide interface by controlled surface reconstruction. The established spin pinning effect can reduce the kinetic barriers in the OER (oxygen evolution reaction). The optimized Fe/MnO@C nanocomposite can be applied for OER in pH-universal electrolytes with low overpotential and small Tafel slope. The synergistic effects in an advantageous crystalline-amorphous core-shell nanocomposite significantly boost the reaction dynamics for water splitting. This research may shed light on the construction of high performance and low cost non-precious metal electrocatalysts for water oxidation.

Nanozyme Rich in Oxygen Vacancies Derived from Mn-Based Metal-Organic Gel for the Determination of Alkaline Phosphatase.

Vacancy engineering as an effective strategy has been widely employed to regulate the enzyme-mimic activity of nanomaterials by adjusting the surface, electronic structure, and creating more active sites. Herein, we purposed a facile and simple method to acquire transition metal manganese oxide rich in oxygen vacancies (OVs-Mn2O3-400) by pyrolyzing the precursor of the Mn(II)-based metal-organic gel directly. The as-prepared OVs-Mn2O3-400 exhibited superior oxidase-like activity as oxygen vacancies participated in the generation of O2•-. Besides, steady state kinetic constant (Km) and catalytic kinetic constant (Ea) suggested that OVs-Mn2O3-400 had a stronger affinity toward 3,3',5,5'-tetramethylbenzidine and possessed prominent catalytic performance. By taking 2-phospho-l-ascorbic acid as the substrate, which can be converted into reducing substance ascorbic acid in the presence of alkaline phosphatase (ALP), OVs-Mn2O3-400 can be applied as an efficient nanozyme for ALP colorimetric analysis without the help of destructive H2O2. The colorimetric sensor established by OVs-Mn2O3-400 for ALP detection showed a good linearity from 0.1 to 12 U/L and a lower limit of detection of 0.054 U/L. Our work paves the way for designing enhanced enzyme-like activity nanozymes, which is of significance in biosensing.

Mixed transition metal-manganese oxides as catalysts in MFCs for bioenergy generation from industrial wastewater

Microbial fuel cell (MFC) technology has attracted growing interest in the past decade for simultaneous bioenergy production and wastewater treatment. These devices require cost-effective cathode catalysts for the oxygen reduction reaction towards their practical implementation. The application of MFC technology for the specific treatment of industrial wastewater, which usually presents persistent pollutants, is also gaining growing attention. This work is aimed at studying the use of mixed manganese oxides with copper and nickel synthesized by co-precipitation in MFC devices fed with industrial wastewater. The new catalysts were assessed in terms of power performance and chemical oxygen removal. Active phases and constructed cathodes were characterized by XRD, EDX and elemental mapping. Among the materials analyzed, the oxide with formula NiMn2O4 offered good power performance, achieving 80% (439 mW/m3) out of the power density obtained with Pt (549 mW/m3). Significant COD removal from industrial wastewater after 168 h of operation was achieved with no previous pretreatment applied.

Farklı Metal (Bakır, Çinko, Kurşun, Kalsiyum ve Mangan) Oksitlerin Sıcak Baca Gazı Kükürt Tutma Aktiviteleri

Bu çalışma, düşük sıcaklıklarda kükürt tutma aktivitesi bilinen beş metal oksitin (CuO, ZnO, PbO, CaO ve MnO) yüksek sıcaklıkta gösterecekleri kükürt giderme performanslarını test etmeyi amaçlamaktadır. Özellikle yüksek kükürt içeren linyitlerin enerji üretimi amacıyla kullanıldığı ülkemizde yüksek kükürt içeriğinin neden olduğu çevresel sorunlar linyit kullanımı için önemli bir sınırlayıcı engeldir. Bu engeli aşmak için önerilen çözümler ise genellikle açığa çıkan sıcak baca gazlarının soğutulması sonrasında kükürtün metal oksit temelli bir adsorbent yardımıyla tutulmasına dayanmaktadır. Yanma prosesine alternatif olan ve temiz kömür teknolojisi olarak bilinen gazlaştırma prosesleri ise sentez gazı (CO ve H2) üzerinden petrol üretimine imkan vermektedir. Kömürün gazlaştırılmasıyla enerji üreten sistemlerde sıcak baca gazlarının soğutulmasının neden olduğu enerji kayıplarını önlemek için, kükürtü sıcak baca gazlarından uzaklaştırmak gerekir. Bu sebeple kükürtün giderimi için kullanılan metal oksitlerin yüksek sıcaklıkta gösterdikleri kükürt giderim aktiviteleri hem çevresel bir sorunu gidermek hem de enerji verimini artırmak adına son derece önemlidir.

Effective hydrogen productions from propane steam reforming over spinel-structured metal-manganese oxide redox couple catalysts

Effective hydrogen productions from propane steam reforming over spinel-structured metal-manganese oxide redox couple catalysts

Porously Assembled 2D Nanosheets of Alkali Metal Manganese Oxides with Highly Reversible Pseudocapacitance Behaviors

Porously assembled 2D nanosheets of alkali metal manganese oxides were synthesized via the flocculation of exfoliated MnO2 nanosheets with alkali metal cations. According to X-ray diffraction and electron microscopic analyses, the MnO2 nanosheets were porously restacked with alkali metal cations, resulting in the mesoporous assembly of lamellar crystallites with surface expansion (∼50−70 m2 g−1). Mn K-edge X-ray absorption spectroscopy clearly demonstrated that manganese ions in the reassembled materials were stabilized in octahedral symmetry with the mixed oxidation state of Mn3+/Mn4+. The present reassembled manganates showed large capacitances of ∼140−160 F g−1 and excellent cyclability of ∼93−99% up to the 1000th cycle. The electrochemical cycling did not induce notable frustration in the crystal structure of manganate nanosheets, underscoring the high structural stability of the reassembled manganates. This study provided strong evidence for the effectiveness of the exfoliation−reassembling method in...

Structure of Nanocrystalline Alkali Metal Manganese Oxides by the Atomic Pair Distribution Function Technique

The atomic scale structures of two nanocrystalline K−Li−Mn−O−I materials obtained through Chimie Douce route in aqueous and acetone solutions have been determined using X-ray diffraction and atomic Pair Distribution Function technique. Both samples have been found to possess a layered-type structure, where the layers are made of edge-shared MnO6 octahedra. With the sample prepared in aqueous solution, the layers are well separated and the interlayer space is occupied by both Li and K atoms. With the sample prepared in acetone solution the Mn−O layers are not so well separated and encapsulate mostly Li atoms. This material exhibits some Li/Mn substitutional disorder as well. The new structural information has been used to explain the electrochemical behavior of the two nanocrystalline materials. Some methodological aspects of the atomic pair distribution function technique and its applicability to study the structure of crystalline and nanocrystalline materials have been discussed as well.

Electron correlation and Jahn-Teller interaction in manganese oxides

The interplay between the electron repulsion $U$ and the Jahn-Teller electron-phonon interation $E_{LR}$ is studied with a large $d$ model for the ferromagnetic state of the manganese oxides. These two interactions collaborate to induce the local isospin (orbital) moments and reduce the bandwidth $B$. Especially the retardation effect of the Jahn-Teller phonon with the frequency $\Omega$ is effective to reduce $B$, but the strong $\Omega$-dependence occurs even when the Coulombic interaction is dominating ($ U >> E_{LR}$) as long as $E_{LR} > \Omega$. The phonon spectrum consists of two components, i.e., the temperature independent sharp peak at $\omega = {\tilde \Omega} = \Omega [(U +4 E_{LR})/U]^{1/2}$ and that corresponding to the Kondo peak. These results compared with the experiments suggest that $\Omega <E_{LR} <U$ in the metallic manganese oxides.

Lattice effects in magnetoresistive manganese perovskites

The discovery of spectacularly large magnetoresistive responses in a class of metallic manganese oxides has raised hopes that these compounds might be of practical utility. But regardless of whether this promise is realized, these materials provide an ideal system in which to elucidate the properties of metals in which electron–lattice interactions play a key role.

Composite polarons in ferromagnetic narrow-band metallic manganese oxides

Moving electrons accompanied by Jahn - Teller phonon and spin-wave clouds may form composite polarons in ferromagnetic narrow-band manganites. The ground-state and finite-temperature properties of such composite polarons are studied in the present paper. By using a variational method, it is shown that the energy of the system at zero temperature decreases with the formation of the composite polaron and the composite polaron behaves as a Jahn - Teller phononic polaron; the energy spectrum of the composite polaron at finite temperatures is found to be strongly renormalized by the temperature and the magnetic field. It is suggested that the composite polaron contributes significantly to the transport and the thermodynamic properties in ferromagnetic narrow-band metallic manganese oxides.

Intrinsic giant magnetoresistance of mixed valence La-A-Mn oxide (A=Ca,Sr,Ba) (invited)

A large intrinsic magnetoresistance has been found near the ferromagnetic transition of metallic manganese oxides with perovskite-type crystal structure. The magnetic and transport properties were measured on bulk and thin-film La1−xAxMnO3+δ with A=Ca,Sr,Ba. Assuming the double-exchange model proposed by Zener [Phys. Rev. 81, 440 (1951); 82, 403 (1951)], the strong dependence of the transport properties on the magnetic field and also on the chemical composition is attributed to the mixed Mn3+/Mn4+ valence.