Porous MnO2 Research Articles

Nitrogen-doped porous biochar spheres/Mn3O4 heterostructure as an efficient sulfur host for high performance lithium-sulfur batteries

Improving the conductivity of sulfur and enhancing the anchoring of lithium polysulfides (LiPSs) are the two key points to obtain high performance and good cyclic stability of lithium sulfur batteries (LSBs). So, a composite material with heterostructure of nitrogen-doping porous carbon spheres and Mn3O4 is designed. Nitrogen and Mn3O4 can relieve the dissolution and shuttling of polysulfides through chemisorption and reduce the loss of active substances. The induced electric field of the heterostructure can further strengthen the adsorption and transformation of lithium ions, thus accelerating the reaction process. The synergetic merits make NPCS/Mn3O4@S nanocomposites exhibit significantly better electrochemical performances than NPCS. At 1.0 C, its initial specific capacity can reach 744 mA h g−1, and can stabilize 600 cycles. When the current density is 2.0 C, the initial specific discharge capacity is 674 mA h g−1, and the reversible capacity is still 478 mA h g−1 after 200 cycles.

Immobilization of polypyrrole on waste face masks using a novel in-situ-surface polymerization method: removal of Cr(VI) from electroplating wastewater

ABSTRACT In this work, polypyrrole (PPy) was synthesized on the surface of waste surgical face masks (SFM) with a novel environmentally-friendly in-situ-surface polymerization approach and used as an adsorbent for removing hexavalent chromium (Cr(VI)). In this method, the SFM surface was activated using KMnO4, resulting in the immobilization of porous MnO2, on which pyrrole can be polymerized efficiently. The novelty of this method is the presence of the oxidant on the surface before the polymerization step, which results in a better surface modification with polypyrrole. This method provides adsorbents with higher adsorption capacity compared to the conventional polymerization method with ammonium persulfate (APS). The adsorbent prepared at the mass ratios of 1.0 and 2.0; respectively, for KMnO4/SFM and pyrrole/SFM showed the highest performance. The adsorbent characterization revealed the successful polymerization of pyrrole on the surface of SFM. Reusability of the KMnO4 and pyrrole solutions were successful with remarkable results, showing the advantage of this technique compared to the conventional polymerization method with APS. The effect of different factors on the adsorption process was investigated. The removal rate was around 98% under the optimum conditions (pH, 2; adsorbent dosage, 3 g L−1; contact time, 60 min). The equilibrium data were well fitted by Langmuir isotherm (R2 = 0.9999). Kinetic investigations revealed that the adsorption process fitted well with the pseudo-second-order model. The adsorbent was regenerated for up to five cycles. One of the most important advantages of the proposed method compared to other methods is the reduction of wastewater during the synthesis process.

High Areal Capacity, Long Cycle Life Li-Air Batteries Enabled by Nano/Micro Hierarchical Porous Cathode.

The limited cycle life of Li-air batteries (LABs) with high areal capacity remains the chief challenge that hinders their practical applications. Here, the study proposes a hierarchical porous electrode (HPE) design strategy, in which porous MnO nanoflowers are built into mesopore/macropore electrodes through a combination of chemical dealloying and physical de-templating procedures. The MnO nanoflowers with 10-30nm pore provides active sites to catalyze the O2 reduction and decomposition of discharged products. The 5-10µm macroscopic pores in the cathode serve as channels of O2 transportation and facilitate the electrolyte permeation. The proposed HPE exhibits a full discharge capacity of 17.49mAhcm-2 and stable cycle life >2000h with a limited capacity of 6mAhcm-2 . These results suggest that the HPE design strategy for LABs can simultaneously provide large capacity and robust cycle life, which is promising for advanced metal-air batteries.

MnO2 nanoflowers-decorated MXene nanosheets with enhanced supercapacitor performance

As typical energy storage devices, the extensive application of the supercapacitors is largely restricted by their relatively low energy storage efficiency, which motivates the development of various advanced electrode materials with sophisticated architectural design. Herein, we put forward a robust and controllable approach to construct a series of hybrid nanoarchitectures consisting of nanoflower-shaped MnO2 nanocrystals grown on super-thin Ti3C2Tx MXene nanosheets (MNF/Ti3C2Tx) via a convenient co-precipitation process. Such a delicate configuration enables the nanoarchitectures to provide prominent structural merits, such as 2D thin-sheet structure with large surface area, porous MnO2 nanoflower frameworks, activated electronic structure, and high electron conductivity. As a consequence, the optimized MNF/Ti3C2Tx electrode manifests superior electrochemical capacitive properties with a maximum specific capacitance of 348.5 F g−1 at 0.5 A g−1, excellent rate property, and reliable cycling stability with 91.9% retention of initial capacitance after 5000 cycles, all of which are more competitive than those of conventional MnO2 and Ti3C2Tx electrodes.

Fabrication of MnO<sub>2</sub> - based electrochemical electrodes for the determination of copper (II) ion in water

Porous MnO2 with a hexagonal crystalline structure was facilely prepared at a low hydrothermal temperature of 90°C, without using any template or capping agent. The as-prepared MnO2 only presented an exceptional electrocatalytic ability by the typical amperometric detection of copper (II) in the presence of super P carbon black as conducting agent, and Nafion as binder. In the present work, to evaluate the detection ability of copper (II) of the MnO2, the graphite plate electrodes (GPE) were modified with MnO2 microflowers and super P carbon and used as electrochemical electrodes for the determanation of copper (II) present in water sources. From the measured results, the fabricated electrodes with excellent copper detection and rapid response demonstrated has high application potential for electrochemical sensors in detection of copper in water resources.

Fabrication of Screen-Printed Electrodes Modified by Hydrothermal MnO2 Microflowers and Carbon for Electrochemical Sensors in Copper Ions Detection

Porous MnO2 microflowers with a hexagonal crystalline structure were facilely prepared at a low hydrothermal temperature of 90°C, without using any template or capping agent. The as-prepared MnO2 only presented an excellent detection ability for copper (II) by a square wave anodic stripping voltammetry in the presence of super P carbon black as conducting agent, and Nafion as binder. In the present work, to evaluate the detection ability of copper (II) in the MnO2 microflowers, chips of screen-printed electrodes (SPEs) having a polyurethane substrate, a silver working electrode, a carbon counter electrode, and a silver pseudoelectrode, were designed. Then, the SPEs chips were modified with MnO2 microflowers and/or super P carbon and used as electrochemical sensors for the detection of copper (II) present in water sources. From the measured results, the fabricated sensors with excellent copper detection in a linear range from 0.625 nM to 15 nM (R2 = 0.9737), and a low detection limit (0.5 nM), high sensitivity (214.05 μA/cm2 nM), and rapid response (180 s) demonstrated high application potential for electrochemical sensors in the detection of copper in water resources.

Ultrathin porous MnO2@C nanosheets for high-performance lithium-ion battery anodes

Engineering ultrathin porous two-dimensional (2D) MnO2/C composites is regarded as an efficient way to achieve high performance of MnO2 anode for lithium-ion batteries (LIBs) because of existence of many features such as shortened ion diffusion pathways and larger surface-controlled capacitance contribution, but they are difficult to prepare because of complex structures. Herein, we contribute a facile strategy for preparing ultrathin porous MnO2/C nanosheets and confirm that the introduced tetraethyl orthosilicate (TEOS) raw material plays a key role in formation of thus MnO2/C nanosheets. The as-prepared MnO2/C composite consists of ultrathin porous conformal carbon coated MnO2 nanosheets whereby integrates the advantages of 2D nanostructure, porous structure and superficial conformal carbon coating so as to improve lithium storage. As a result, this composite exhibits impressive performance, showing high capacity, long cycle life and improved rate capability, with 747.6 mA h g−1 after 400 cycles at 200 mA g−1 and 542.6 mA h g−1 after 420 cycles even at 1000 mA g−1. Based on systematic material and electrochemical characterizations we confirm that the outstanding performance of the as-prepared MnO2/C composite benefits from its well-designed nanostructure. Besides, we believe that this work can enlighten researchers to synthesize other 2D metal oxide/carbon composites for energy storage or other applications.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Preparation of Porous and Durable Metakaolin-Based Alkali-Activated Materials with Active Metal as Composites for Catalytic Wet Air Oxidation

Novel porous and durable metakaolin-based alkali-activated materials (MK-AAMs) with active metal as composites were produced to degrade bisphenol A (BPA) in catalytic wet air oxidation (CWAO). Two composite producing processes were employed. The first process consisted of mixing metakaolin (MK), a foaming agent and active metal oxide (CuO, MnO2) in a strongly alkaline solution of K2SiO3 and KOH. Paste was cured under microwave radiation to produce porous CuO and MnO2 composites. A porous blank MK-AAM was produced as described above but without active metal and was used as a reference as well. Cu(OH)2 composite was produced by refluxing a blank MK-AAM in 0.5 M CuSO4 solution for 24 h. The specific surface area (SSA) of the reference, CuO, MnO2, and Cu(OH)2 composites were 36, 53, 61, 89 m2/g, respectively. Mechanical durability was determined in terms of compressive strength and 2.8, 3.4, 3.2, 3.6 MPa were received, respectively. The activity of the reference and the composites were tested in CWAO at 1 MPa and 150 °C for 5 h by using an aqueous model solution of BPA. Under the optimal conditions for CWAO (pressure: 1 MPa; temperature: 150 °C; initial pH 5–6; c[catalyst]: 4.0 g/L) with Cu(OH)2 composite, the BPA and total organic carbon (TOC) conversions of 100% and 53% were reached. During 5 h oxidation, the composites degraded due to the combined effect of erosion (1.5 wt%) and active metal (Cu, Mn) leaching (1.1 wt%, 3.6 wt%). It was proposed that BPA can be degraded energy-efficiently via CWAO into less harmful compounds under mild reaction conditions without losing the desired properties of the composites.

Electric-field oriented self-assembly of Mn3O4 nanostructures driven by liquid plasma discharge for super capacitor

Fabrication of low-cost, uniform size, and binder-free nanomaterials via contact glow discharge electrolysis (CGDE) for high performance supercapacitors is still a great challenge. In this work, by utilizing the CGDE method as a template, the rapid synthesis of two different morphologies of Mn3O4 nanostructures through a one-step liquid plasma discharge deposition (LPDD) method is proposed and demonstrated. The two uniform nano-octahedron and nano-sheet Mn3O4 structures are grown upon the different electric field orientations under a low DC voltage. The transportation of ions is dependent on the electrical field direction leading to the formation of different nanostructures. Upon the horizontal electric field to the grown substrate, the Ostwald ripening effect is dominant in the growth process of single-crystalline Mn3O4 nano-octahedra, which exhibits high crystallinity and geometric symmetry with a side length of 40 nm. In contrast, the hydrothermal effect assists in the formation of Mn3O4 nano-sheet when the electrical field is perpendicular to the substrate. The continuous transportation of ions promotes the fast growth of ultra-thin and porous Mn3O4 polycrystalline nano-sheets. The binder-free nano-sheet Mn3O4/carbon composite electrode delivers a higher specific capacitive (488 F g−1) and remarkable cycle life (10,000 cycles; 99.1% capacity retention). This work addresses a facial, cost-effective, and scalable path of the production of nanostructures with different morphologies simply by the operation of an electric field.

Growth of Flower-like MnO2 on Porous ZIF-67 for Achieving Enhanced Supercapacitive Properties

Zeolitic imidazolate framework (ZIF)-supported flower-like porous MnO2 (ST@ZIF-67/MnO2) was fabricated through SiO2-guided preparation of the ZIF precursor and subsequent in situ synthesis and deposition of MnO2. The specific porous structure can effectively shorten the ion transport channels, expose more active sites, and improve the tolerance toward volume expansion during the cyclic process, thus resulting in enhanced supercapacitive properties. Typically, the ST@ZIF-67/MnO2-based electrode delivered a high specific capacitance of 278.6 F g–1 at 0.5 A g–1, which is almost 10 times that of pristine ZIF-67 and 1.5 times that of the composite without using the SiO2 template (ZIF-67/MnO2). Additionally, the electrode showed good electrochemical cycling stability with 80.3% retention after 10, 000 cycles at 10 A g–1. Our strategy of growing porous transition metal oxides on ZIFs provides a viable pathway for developing efficient electrode materials for energy storage devices.

Synthesis of porous Mn2O3 architecture for supercapacitor electrode application

Transition metal oxides (TMOs) are a potential candidate for supercapacitor due to its outstanding characteristics such as cheap, abundant and non-toxic. But poor electron conductivity and large volume expansion at charge/discharge process limit their practical application as electrode materials. It is a feasible strategy to design porous TMOs which could provide high surface area and more electroactive sites to improve electrochemical performance. Herein, a porous Mn2O3 was synthesized by hard-template method using MCM-41 as template. It exhibits superior pore property of high specific surface area of 382 m2 g−1. And applied it as electrode material for supercapacitor, the porous Mn2O3 shows higher specific capacitance of 102 F g−1 compared to 4.88 F g−1 and 2.28 F g−1 of two types of block Mn2O3 with surface area 7.27 m2 g−1 and 2.67 m2 g−1 at discharging current density of 0.2 A g−1. Furthermore, it exhibits excellent long cycle stability in that specific capacitance remains stable after 5000 cycles (137% of the initial value). This research demonstrates that the porous Mn2O3 has broad potential as promising electrode materials for supercapacitors.

A novel hierarchical porous carbon-supported MnO2 nanofibers composite with three-dimensional interpenetrating network structure as a high-performance supercapacitor

For improving the conductivity of porous carbon and the utilizations of its pore structures, a hierarchical porous carbon (HPC) had been developed with highly fluffy three-dimensional (3D) continuous network structure. Using the HPC as a support, a novel MnO2@HPC composite with 3D interpenetrating network structure was prepared as electrode material of supercapacitor via simple hydrothermal method. When the hydrothermal reaction temperature was 100°C, the MnO2 nanofibers (∼5 nm) were uniformly grown on and within the fluffy 3D porous network of the HPC, forming a composite with interpenetrating network structure. The as-prepared composite (MnO2@HPC-100) exhibited the characteristics of both electric double-layer capacitance and pseudo-capacitance, which had a high specific capacity of 368 F g−1 at a current density of 0.5 A g−1 and 186 F g−1 at 10 A g−1 (50.5% retention). In addition, the asymmetric supercapacitor device was assembled with a relatively high energy density of 88.2 Wh Kg−1 at a power density of 162 W Kg−1. The device had a high capacity retention rate of 95% after 10000 cycles, and the coulomb efficiency was stable at 99.7%, showing the excellent stability of the composite. Therefore, the MnO2@HPC-100 composite has great application prospects in energy storage.

Modifying acidic oxygen production properties of PbO2 by porous Mn2O3 microspheres for boosting stability

Designing active and durable cost-effective electrocatalysts for catalyzing the oxygen evolution reaction (OER) under a strongly acidic environment is a highly promising approach for OER-associated sustainable energy supplies. Herein, a Pb-Sn-Ca/α-PbO2/β-PbO2-Mn2O3 (PSC/PbO2-Mn2O3) composite electrode is fabricated via a simple two-step process. First, porous Mn2O3 microspheres are synthesized by the solvothermal method. Then, a PSC/PbO2-Mn2O3 composite electrode with a special embedded structure is prepared through the introduction of Mn2O3 by composite electrodeposition. The low OER overpotential (621 mV) of the PSC/PbO2-Mn2O3 (12 g L−1) composite electrode is reduced by 445 mV compared with that of the industrial Pb-(0.76 wt%) Ag electrode at a current density of 50 mA cm−2. In addition, it shows a service life of up to 91 h at a high operation current density of 1.5 A cm−2 in acidic media (3.06 g L−1H+), which indicates its excellent stability. Therefore, this work not only demonstrates a design for a durable and high-efficiency electrocatalyst for acidic water oxidation but also provides strategies for the synthesis of advanced electrocatalytic electrodes.

In-situ construction of Mn–Fe mixed oxides nanoparticles on reduced graphene oxide with superior lithium storage property

In this paper, porous Mn3O4–Fe3O4 nanoparticles with highly uniform composition are in-situ anchored on reduced graphene oxide (rGO) nanosheets by a simple cyanometallic framework template method. Thanks to the synergistic effects between the porous Mn3O4–Fe3O4 nanoparticles and the well-conductive rGO nanosheets, the Mn3O4–Fe3O4/rGO composites present superior electrochemical lithium storage performances with a great reversible capacity of 1013 mAh g−1 after 100 cycles at 0.1 A g−1, satisfactory rate capability of 510 mAh g−1 at 3.0 A g−1, and eminent long-term cycle stability of 804 mAh g−1 after 500 cycles at 0.5 A g−1. It is demonstrated that the rGO can not only act as a conducting matrix, but also buffer the volume expansion and avoid the aggregation of the Mn3O4–Fe3O4 nanoparticles during charging-discharging. The work provides a simple strategy for designing and fabricating advanced multi-component metal oxide-based anodes for high-performance lithium-ion battery.

Mullite-bonded porous SiC-based Mn3O4–Ni system: control of electrical resistivity, flexural strength, and extrusion

Mullite-bonded porous SiC-based Mn3O4–Ni system: control of electrical resistivity, flexural strength, and extrusion

Amphiphilic-molecular templated porous β-MnO2 for high-performance rechargeable aqueous Zn-MnO2 batteries

Compared with Li-ion batteries, rechargeable aqueous Zn-ion batteries (RAZIBs) offer energy storage with low cost and good safety. Nevertheless, the irreversible structural transformations and retarded reaction kinetics that always accompany manganese-based materials, which directly lead to low capacity and poor cycling stability, substantially hinder their practical application in large-scale energy storage. Herein, the introduction of mesopores in β-MnO 2 cathode is demonstrated to be effective in solving the above problems, by employing poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) template (P123) as pore-forming agent. The assembled porous β-MnO 2 /Zn full battery delivered a highly reversible capacity of 333 mAh g −1 under 0.1 A g −1 , superior capacity retention of 88% after 1000 cycles under 1.0 A g −1 and great rate capability (87 mAh g −1 at 2 A g −1 and 56 mAh g −1 at 3 A g −1 ). In addition, the structural evolution of porous MnO 2 during cycling, as well as the impact of template concentration on the pore structures, is further studied. A novel strategy for optimizing the electrochemical performance of RAZIBs is provided by this structural modulation strategy.

MOF-derived MnO@C with high activity for electric field-assisted catalytic oxidation of aqueous pollutants

The activation of oxygen (O2) under room condition is important for the utilization of air to perform oxidation. Here, we report a porous carbon-encapsulated MnO (MnO@C) derived from Mn metal-organic framework (MOF)grown in-situ on a graphite felt (GF) support. The MnO@C exhibits superior catalytic activity in an electric field-assisted catalytic oxidation system for the degradation of organic pollutants under room condition. The catalytic oxidation reaction applies a surface reaction pathway in which the surface-bound chemisorbed oxygen species are electro-oxidized and then involved in the oxidation of co-adsorbed organic pollutants. The abundant oxygen vacancies and oxygenated functional groups in MnO@C provide active sites for the chemisorption of O2, and its conductive mesoporous structure allows facile electrons and mass transfer. As a result, the MnO@C/GF catalyst displays quite high turnover frequency (TOF) value as 0.038 mg-TOC mg-MnO−1 min−1, which is 6.66 times higher than that of the MnO/GF catalyst prepared by impregnation method as a comparison. With the aid of + 1.0 V of positive electric field, the catalytic oxidation system exhibits extensive effectiveness in mineralizing a variety of dyes, pharmaceuticals, personal care products, and phenolic compounds under room condition with significantly enhanced biodegradability.

Carbon nanosheets/MnO2/NiCo2O4 ternary composite for supercapacitor electrodes

Potassium citrate has been reported to fabricate carbon nanosheets (CNS) through high-temperature calcinations. To integrate electrical double-layer capacitive CNS with high-pseudocapacitive metal oxides, a novel CNS/MnO2/NiCo2O4 ternary composite is developed by growing NiCo2O4 nanoneedles on porous CNS/MnO2 nanosheets arrays, in which, the CNS/MnO2 template was prepared by the redox reaction between CNS and KMnO4. Through optimizing the dosage of CNS/MnO2 template, the CNS/MnO2/NiCo2O4–0.1 composite prepared with 0.1 g CNS/MnO2 presents the highest capacitance of 1254 F g−1, and the capacitance retains 81.9% after cycled for 5000 cycles. The asymmetric supercapacitor device consisted of CNS/MnO2/NiCo2O4–0.1 positive electrode and CNS/CNTs negative electrode delivers a capacitance of 161 F g−1 at 0.5 A g−1. The energy density reaches the maximum value of 22.2 Wh kg−1 at 727.9 W kg−1. The superior performance of the proposed ternary composite can be ascribed to the high conductivity of CNS and the improved ion/charge transfer by porous MnO2 nanosheets arrays. Furthermore, the combination of NiCo2O4 nanoneedles with MnO2 nanosheets contributes to much more pseudocapacitance by playing a synergistic effect.

Biomass-derived porous carbon-incorporated MnO2 composites thin films for asymmetric supercapacitor: synthesis and electrochemical performance

Biomass-derived porous carbon-incorporated MnO2 composites thin films for asymmetric supercapacitor: synthesis and electrochemical performance