Synergistically enhanced electrocatalytic activity of cerium oxide/manganese tungstate composite for oxygen reduction reaction

Journal of Materials Science: Materials in Electronics - Noble metal-free and earth abundant metals were considered as promising candidates for the development of electrocatalysts towards oxygen...     

Synthesis of manganese dioxide/reduced graphene oxide composites with excellent electrocatalytic activity toward reduction of oxygen

MnO₂/reduced graphene oxide(RGO) composites were synthesized by a facile and effective polymer-assisted chemical reduction method. The synthetic MnO₂/RGO composites have a uniform surface distribution and large coverage of MnO₂ nanoparticles onto graphene, which were characterized with scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and cyclic voltammetry. The synthetic MnO₂/RGO composites were studied with respect to its electrocatalytic activity toward the reduction of oxygen in alkaline media and were found to possess a good electrocatalytic activity toward the four-electron reduction of oxygen.     

Edge reconfiguration of N,P-codoped carbon boosts oxygen reduction electrocatalysis

Journal of Materials Science - Conversion of heteroatom-doped sites to carbon defects has been developed recently as an efficient strategy to build advanced metal-free carbon electrocatalysts for...     

Synergy in hybrid polymer/nanocarbon composites. A review

The aim of this review article is to report the most recent developments in the understanding of and beliefs about the properties of polymer hybrid composites that are reinforced with various combinations of nanometer-sized carbon and mineral fillers. The discussions are primarily focused on an analysis and comparison of the electrical, thermal, and mechanical properties. It is shown that the introduction of a mixed (hybrid) system of filler nanoparticles into polymer matrices enhances the macro- and microproperties of the composites as a result of the synergistic interactions between the fillers and the simultaneous creation of a unique filler network in the polymer. The synergy of various types of carbon nanofillers and combinations of nanocarbon materials with inorganic fillers manifests itself as modifications of most of the properties of hybrid polymer composites relative to the properties of a polymer system containing a single filler. The reinforcing effect is related to the structure and particle geometry of the hybrid fillers, the interactions between the fillers, the concentrations and the processing methods.The existence of synergy between different types of carbon nanofillers, as well as with mineral fillers, shows great potential and could significantly increase applications of carbon-based nanomaterials.     

Construction of hierarchical Ti3C2Tx@TiO2/MoS2 covered manganese oxides for advanced oxygen evolution electrocatalysis

Nano-level manganese oxide particles deposited on the surface of nickel foam (NF/MnO_x) have a great potential in the field of electrochemical water splitting. In addition, these hierarchical Ti₃C₂T_x@TiO₂/MoS₂ powders consist of non-cubic TiO₂ derived from defect sites of Ti₃C₂T_x and MoS₂ sheets preventing inner Ti₃C₂T_x@TiO₂ from corrosion of electrolyte covered these layered Ti₃C₂T_x particles accompanied with heterojunction interface and plentiful exposed active sites. In this work, the electrochemical performance of multicomponent mixed manganese oxides prepared by rapid electrodeposition is restricted by the poor electrical conductivity, but the addition of Ti₃C₂T_x@TiO₂/MoS₂ can improve the surface area to electrolyte, enhance the Faradaic reaction and reduce ion diffusion length. Thus, the NF/MnO_x-Ti₃C₂T_x@TiO₂/MoS₂ sample can incorporate these electrochemical advantages of NF/MnO_x and Ti₃C₂T_x@TiO₂/MoS₂. By characterization of as-prepared samples, it finds that these samples are combined amorphous phases with crystalline, so they can commonly improve the electrochemical performance by synergistic reaction. As the result of electrochemical test shown, the NF/MnO_x-Ti₃C₂T_x@TiO₂/MoS₂ sample performs excellent oxygen evolution performance and possesses a low overpotential of 270 mV with the current density of 10 mA/cm². The stability of the NF/MnO_x-Ti₃C₂T_x@TiO₂/MoS₂ sample is evaluated under 10 mA/cm² for 42 h and the overpotential maintains unchanged during the whole test. Thus, the NF/MnO_x-Ti₃C₂T_x@TiO₂/MoS₂ sample can serve as excellent catalysts for oxygen evolution reaction.

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One-step through-mask electrodeposition of a porous structure composed of manganese oxide nanosheets with electrocatalytic activity for oxygen reduction

Potentiostatic electrolysis of a mixed aqueous solution of Bu₄NBr and MnSO₄ at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br⁻ and Mn²⁺ ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu₄N⁺ and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO_x-modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode.     

含锰磁铁相还原氧化锰矿的浸出工艺

针对含锰磁铁相的还原氧化锰矿浸出效果差的问题,以云南文山示范线还原氧化锰矿、浸出尾渣为主要研究对象,考察起始酸度、浸出时间和浸出温度对锰磁铁相浸出反应的影响;在明确锰磁铁相浸出规律基础上,优化浸出工艺。结果表明,锰磁铁相在较高酸浓度梯度下,能保持较快的浸出速率;先后采用质量浓度为48.02 g/L的起始酸浸出一氧化锰相,76.44 g/L的浸出锰磁铁相的两段逆流浸出工艺,比单段浸出工艺,锰浸出率从82.31%增加到92.17%,酸耗(酸矿质量比)从0.55减少到0.50。     

Tetrapropylammonium-manganese oxide/polypyrrole hybrid nanocomposite thin films as novel electrode materials for supercapacitors

Tetrapropylammonium-manganese oxide/polypyrrole (TPA-MO/Ppy) hybrid nanocomposite with molar ratios of TPA-MO/Ppy 4:1, 2:1 and 1:1 were successfully prepared by a combination of in situ polymerization and the sol–gel process. The microstructure of hybrid nanocomposite thin film samples was observed to be significantly affected by synthesis parameters, most notably the molar ratio of reactants and post-synthesis calcination temperature. Samples with higher pyrrole contents appeared to possess higher specific surface areas, which ranged from 132 to 281 m² g⁻¹. SEM micrographs indicated that all nanocomposite thin films were highly fibrous and porous in nature. Optimum doping of manganese oxide with conducting polypyrrole had led to the formation of novel nanocomposite with nanofibrillar structures which consisted of interconnected manganese oxide and polypyrrole nanoclusters. Optimized nanocomposite films showed higher charge capacities which could be attributed to enhanced material utilization as a result of optimized microstuctural parameters in particular, specific surface areas.     

One-pot synthesis of Pt/carbon nanotubes by self-regulated reduction for electrocatalysis

This paper describes a method for size-controlled synthesis of Pt nanoparticles and their attachment to the sidewalls of multiwall carbon nanotubes (CNTs) by self-regulated reduction of sodium n-dodecyl sulfate (SDS), without surface pretreatment. The size of the Pt nanoparticles is controlled by adjusting the concentration of SDS. When Pt/CNTs are heated to 500 degrees C in N2 atmosphere, Pt nanochains are formed on the CNTs; some of these nanochains contain small islands. Electrochemical measurements confirm that the electroactivities of the Pt/CNT nanocatalysts increase with a decrease in the size of the Pt nanoparticles. Additionally, comparing with the heated Pt/CNT nanocatalysts containing smooth Pt nanochains, the heated Pt/CNT nanocatalysts containing Pt nanochains with small Pt islands show higher electrocatalysis activities and stability.     

Materials for high-temperature oxygen reduction in solid oxide fuel cells

Solid state ionic devices such as fuel cells and oxygen separation membranes require the adsorption of oxygen molecules, their dissociation into oxygen atoms, oxidation by charge exchange and entry of the resultant ion into the solid phase. The cathodes capable of sustaining these processes must themselves be stable in the high temperature environment of air with a significant water vapour content, and compatible chemically and mechanically with the contacting solid phase, normally an electrolyte. As charge transfer materials obviously a high electronic conductivity is imperative, and some degree of ionic conductivity can serve to delocalise the oxidation process, thus reducing polarisation. In the present review the evolution of these cathode materials and their present status will be presented.     

Interface engineering of Co3O4---SmMn2O5 nanosheets for efficient oxygen reduction electrocatalysis

Interface engineering is an efficient strategy to modify electronic structure and further improve electrocatalytic activity. Herein, crystalline/amorphous heterostructured Co₃O₄–SmMn₂O₅ nanosheets (Co₃O₄–SMO NSs) have been synthesized by coupling of SMO (electron acceptor) with higher Fermi-level Co₃O₄ (electron donor), via a one-step hydrothermal method followed by calcination. The resulting Co₃O₄–SMO NSs display higher half-wave potential and specific activity than those of pure SMO or Co₃O₄. In addition, Co₃O₄–SMO NSs exhibit superior stability and methanol tolerance. The crystalline/amorphous heterostructure and the electron interaction between SMO and Co₃O₄ result in interfacial charge transfer. This leads to more active valence states and more oxygen vacancies, optimizing the adsorption energy of O species and expediting electron migration, thus boosting oxygen reduction reaction (ORR) catalytic performance. This study provides a promising strategy to design efficient ORR electrocatalysts by interfacial engineering.     

Supramolecular confinement of single Cu atoms in hydrogel frameworks for oxygen reduction electrocatalysis with high atom utilization

Single-atom catalysis has emerged as a cutting-edge field in heterogeneous catalysis. Considerable efforts have been devoted to developing versatile methodologies for synthesizing single-atom catalysts, however, the main thrust in this field is to fundamentally understand the intricacies of a catalyst and their performance on a specific reaction by complimenting different techniques. Here we demonstrate a supramolecular hydrogel strategy to effectively isolate copper atoms on interconnected carbon fibers as efficient electrocatalysts for the alkaline oxygen reduction reaction (ORR). The Cu–N2 coordination state and the atomic dispersion were confirmed by X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. Additionally, the atom utilization (η_atom), which is the ratio between Cu(I) sites participating in the catalysis and the total Cu(I) sites available, has been investigated via surface-interrogation scanning electrochemical microscopy (SI-SECM) technique. The over 90% atom utilization of the synthesized Cu SACs is very close to the theoretical value (100%) for SACs, implying the proposed supramolecular approach can enable the ultrahigh exposure of Cu sites. The in situ time-resolved titration of SI-SECM and first-principal calculations further support the remarkable ORR activity on isolated Cu–N2 sites.     

Large-scale production of holey carbon nanosheets implanted with atomically dispersed Fe sites for boosting oxygen reduction electrocatalysis

Atomically dispersed metals stabilized by nitrogen elements in carbon skeleton hold great promise as alternatives for Pt-based catalysts towards oxygen reductio...     

Biochar supported manganese based catalyst for low-temperature selective catalytic reduction of nitric oxide

Clean Technologies and Environmental Policy - This research work aims to study the performance of biochar-supported manganese-based catalysts for conversion of NOx in the selective catalytic...     

Hierarchical manganese oxide/carbon nanocomposites for supercapacitor electrodes

MnO₂/carbon nanocomposites with hierarchical pore structure and controllable MnO₂ loading have been synthesized using a self-limiting growth method. This was achieved by the redox reactions of KMnO₄ with sacrificed carbon substrates that contain hierarchical pores. The unique pore structure allows the synthesis of nanocomposites with tunable MnO₂ loading up to 83 wt.%. The specific capacitance of the nanocomposites increased with the MnO₂ loading; the conductivity measured by electrochemical impedance spectroscopy, on the other hand, decreased with increasing MnO₂ loading. Optimization of the MnO₂ loading resulted in nanocomposites with high specific capacitance and excellent rate capability. This work provides important fundamental understanding which will facilitate the design and fabrication of high-performance supercapacitor materials for a large variety of applications.     

Synthesis and electrical properties of graphene–manganese oxide hybrid nanostructures

Journal of Materials Science: Materials in Electronics - In the present contribution, grapheme–manganese oxide hybrid nanostructures (G/MnO2) were synthesized via rapid and facile microwave...     

Manganese–Schiff base complex immobilized silica materials for electrocatalytic oxygen reduction

Curtailment of platinum catalysts loading in fuel cell is a recent central issue. As substitutes, these days several organic metal chelate compounds having featured moieties of M–N₄ or M–N₂O₂ (M = transition metal ion) are being used as cathode catalysts in fuel cells. Here, in this study, we report in detail the electrocatalytic activity of manganese–Schiff base complexes for oxygen reduction reaction in 0·05 M HClO₄ at room temperature. Actually, [Mn(salen)]⁺: [N,N′-bis(salicylaldehyde) ethylenediimino manganese(III)]⁺ and [Mn(salophen)]⁺: [N,N′-bis(salicylaldehyde)-1,2-phenylenediimino manganese(III)]⁺ were introduced into/onto the MCM-41 type silica spheres and used for the electrocatalytic reduction of oxygen. Synthesized materials were characterized by UV–Vis, FT–IR and electrochemical techniques. Significant low overpotential for oxygen reduction in 0·05 M HClO₄ on [Mn(salen)]⁺- and [Mn(salophen)]⁺-incorporated silica-modified glassy carbon electrodes was observed.     

Hierarchical,seamless, edge-rich nanocarbon hybrid foams for highly efficient electromagnetic-interference shielding

Lightweight,flexible,ultrahigh-performance electromagnetic-interference (EMI) shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1D carbon nanotubes (CNT) and carbon nanofibers (CNF) with 2D edge-rich graphene (ERG) are used to form a lightweight,flexible CNT-ERG-CNF hybrid foam.This foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3D hybridized carbon nanostructure.Multistage conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interracial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness (SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness (SE) exceeding 55.4 dB in the X-band while the specific SE (SSE,SE divided by mass density) achieves 9200 dB cm3 g-1,which surpasses that of nearly all other carbon-based composite materials.Furthermore,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic bending.Remarkably,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.     

流态化低温还原氧化锰矿工艺的特点

对中国科学院过程工程研究所设计开发的流态化低温还原氧化锰矿的工艺进行介绍,并与传统高温还原工艺进行对比,分析其优势。结果表明:流态化低温还原氧化锰矿工艺中单位煤耗仅约为传统高温工艺的60%;单台设备的处理能力可达600t/d;适用于总铁质量分数T_(Fe)≤15%、结晶水质量分数低于18%的氧化锰矿;还原过程温度低,副反应少,杂质浸出率低;尾气通过工艺过程的自身反应,无须脱硫、脱硝,可达到国家排放标准。