Porous MnO2 Research Articles

First-principles study of carbon capture and storage properties of porous MnO2 octahedral molecular sieve OMS-5

Based on the experimentally determined framework structure of porous MnO2 octahedral molecular sieve (OMS)-5, we used density functional theory-based calculations to evaluate the effect of Na+ cation on pore dimensionality and structural stability, and the interaction between CO2 and OMS-5. We quantified the formation energy of one CO2/unit tunnel and two CO2/unit tunnel, and projected the electronic density of states on the OMS-5 framework, CO2 molecules, and Na+ cations to reveal their individual contributions and bonding nature. Partial charge densities were also calculated to investigate CO2 adsorption behavior in the OMS-5. Our studies predict the initial stage and driving force for the adsorption of CO2 in the OMS-5, guiding the OMS material design for carbon capture and storage applications.

Biotemplate derived three dimensional nitrogen doped graphene@MnO2 as bifunctional material for supercapacitor and oxygen reduction reaction catalyst

Natural diatomite with abundant pores was used as a biotemplate for the massive production of three-dimensional (3D) porous graphene by chemical vapor deposition method. Subsequent template removal and nitrogen doping treatment yield nitrogen doped 3D graphene with preserved shape and complex internal features of the diatomite. After further deposition with MnO2 nanosheets, the N-doped 3D graphene@MnO2 (N-G@MnO2) hybrid exhibited excellent supercapacitor and good oxygen reduction reaction (ORR) performance. Accordingly, the porous N-G@MnO2 electrode exhibited a high specific capacitance (411.5 F g−1) and a good cycling performance (88.3% capacitance retention after 4000 charge/discharge cycling test). When tested in a two-electrode configuration, N-G@MnO2 achieved a wide potential window up to 1.8 V with a high energy density of 46.1 Wh kg−1. Furthermore, the as-prepared N-G@MnO2 showed good performance in oxygen reduction reaction, which is comparable to those of commercially available Pt/C electrode. The enhanced capacitive and electrocatalytic properties and stability is due to the synergistic interactions between the porous 3D graphene and MnO2 nanosheets. The results indicate that the 3D N-G@MnO2 could be useful for supercapacitor and ORR catalyst.

Greatly Enhanced Faradic Capacities of 3D Porous Mn3O4/G Composites as Lithium-Ion Anodes and Supercapacitors by C–O–Mn Bonding

Through C-O-Mn bonding, graphene nanosheets are homogeneously dispersed in porous Mn3O4 to take full advantages of porous Mn3O4 and graphene nanosheets, making the as-formed three-dimensional porous Mn3O4/reduced graphene oxide (rGO) composite exhibit good electrochemical performance. Besides, C-O-Mn bonding is demonstrated to greatly promote the Faradic reactions of the composite, resulting in the enhancement of its real capacity in supercapacitor (SC) electrodes as well as lithium-ion battery (LIB) anodes. By simply fine-tuning the content of graphene (<7 wt %), the composite with 2.8 wt % of rGO delivers a high capacitance of 315 F g-1 at 0.5 A g-1 with a high rate capability of 64.7% at 30 A g-1 and an excellent cycling stability of 105% (5 A g-1, 5000 cycles) as an SC electrode. Also, the one with 6.9 wt % rGO can present a reversible capacity of more than 1500 mAh g-1 at 0.05 A g-1 as the LIB anode, the highest value reported to date, which remains 561 mAh g-1 at 1 A g-1.

A Novel Hydrogen Peroxide Amperometric Sensor Based on Hierarchical 3D Porous MnO2−TiO2 Composites

AbstractA novel nanocomposite electrode based on hierarchical 3D porous MnO2−TiO2 for the application in hydrogen peroxide (H2O2) sensors has been explored. This electrode was fabricated by growing TiO2 cross‐linked nanowires on a commercial fluorine tin oxide (FTO) glass via a hydrothermal process and subsequent deposition of 3D honeycomb‐like MnO2 nanowalls using an electrodeposition method (denoted as 3D MNS‐TNW@FTO). The obtained 3D MNS‐TNW@FTO electrode was characterized by scanning electron microscopy (SEM), Raman spectroscopy, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). Based on such a unique 3D porous framework and the existence of MnO2, the electrode demonstrates a good performance in the detection of H2O2, with two linear ranges from 9.8 to 125 μM and 125 μM–1.0 mM, a good selectivity of 8.02 μA mM−1 cm−2, and a low detection limit of 4.5 μM. In addition, the simplicity of the developed low‐cost fabrication process provides an efficient method for the mass production of electrocatalytical MnO2−TiO2 nanocomposites on commercial FTO glass for H2O2 sensing applications and can be adapted for other electrochemical sensors for various biochemical targets. It thus is beneficial for the practical usage in bioanalysis.

Self-Assembly Synthesis and Electrochemical Performance of Partially Reduced Graphene Oxide Supported Hierarchical MnO2 Nanonocomposite for Supercapacitor

Partially reduced graphene oxide supported hierarchical birnessite-type manganese oxide (MnO2) nanonocomposite (MnO2-pGO) with large surface area (116 m2 g-1) were successfully synthesized by a facile ultrahigh dilute vesicle solution approach, via surfactant Hexadecyltrimethylammonium bromide (CTAB) and sodium dodecylbenzenesulfonate (SDBS), as a structure-directing agent. The resultant structure exhibit hierarchical porous MnO2 nanocluster, which were self-assembled from elongated nanorods and grafted successfully on the surface of the pGO nanosheets. Furthermore, the obtained MnO2-pGO nanocomposite was found to exhibit favorable electrochemical activity showing ultra-high specific capacitance of (282 F/g at 0.5 A/g), the enhanced rate capability of (67.7%) at 10 A/g), the most stable capacitance retention (91.4 %of its initial capacitance was retains after 5000 cycles, with ∼100% Coulombic efficiency). The result suggests that the approach is not only effective to deposit MnO2 over the pGO sheets, but also offered great promise to prepare other pGO- metal oxide composite electrode materials for supercapacitor.

Nanostructured Mn2O3/Pt/CNTs selective electrode for oxygen reduction reaction and methanol tolerance in mixed-reactant membraneless micro-DMFC

Mixed-reactant microfluidic direct methanol fuel cells (MR-μDMFCs) have the feature of achieving higher volumetric energy density in comparison with other DMFCs. The main challenge for the development of MR-μDMFC arises from the need for selective electrocatalysts, especially for the oxygen reduction reaction (ORR). In the present work, we report the two-step synthesis of a binder-free Pt and Mn2O3 based catalyst by pulsed laser deposition. First an ultra-low loading Pt layer is deposited directly on carbon nanotubes and further coated with a porous Mn2O3 layer. The resulting binary material exhibits practically identical electrocatalytic activity to that of Pt towards ORR in alkaline media. Interestingly, it shows no activity for the methanol oxidation reaction (MOR), in contrast with Pt. Furthermore, the Mn2O3/Pt cathode demonstrates to be tolerant to methanol concentration as high as 5 M. The results suggest that the superficial Mn2O3 component discriminates between the molecular size of O2 and MeOH, allowing the former to reach the inner Pt layer and impeding the diffusion of the latter. The RRDE studies reveal that the ORR on both Pt/CNTs and Mn2O3/Pt/CNTs, is carried out through a 3.9 electron transfer. Lastly, the bilayer cathode is tested in a membraneless micro direct methanol fuel cell (ML-μDMFC) under mixed-reactant conditions, producing an OCV of 0.54 V and a maximum power density of 2.16 mW cm−2.

Vertically Standing MnO2 Nanowalls Grown on AgCNT-Modified Carbon Fibers for High-Performance Supercapacitors

Large-scale ultrathin γ-MnO2 nanosheets form a continuous wall-like enclosed network directly grown onto the surface of carbon cloth (CC) fibers. In a simple green electrochemical deposition process, the CCs were pretreated under acid condition and subsequently attached by carbon nanotubes with silver nanoparticles (AgCNTs), forming a three-dimensional (3D) hierarchical heterostructure of MnO2-decorated AgCNT CC fibers (MnO2-AgCNT-CC). The structure, phase purity, and morphology of the samples were characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The MnO2-AgCNT-CC composite had high specific capacitance (up to 325 F/g at 1 A/g) and long cycle-life stability. These outstanding electrochemical characteristics were attributed to the unique 3D porous MnO2 nanowalls and AgCNT composites, increasing ion-accessible surf...

Cable-like double-carbon layers for fast ion and electron transport: An example of CNT@NCT@MnO2 3D nanostructure for high-performance supercapacitors

A unique nanostructure consisting of CNTs as carbon matrix, and were sequentially coated with silicon dioxide, N-doped porous carbon tube (NCT) and MnO2 nanoflowers, the final CNT@NCT@MnO2 composites with large internal voids between CNT and NCT. CNT@NCT@MnO2 combines the nanostructural advantages of internal voids and the N-doped porous carbon, presenting fast diffusion paths for ions and electrons, high conductivity and large surface areas. When used as an anode material in supercapacitors, the CNT@NCT@MnO2 tube-in-tube hierarchical nanostructure exhibite a remarkably excellent electrochemical behavior with a specific capacitance (Csp) of 210 F g−1 at the current density of 0.5 A g−1. Moreover, all-solid-state asymmetrical supercapacitors (ASCs) were fabricated using the CNT@NCT@MnO2 composites as anode and the CNT@NCT as cathode, Na2SO4/PVA gel as the electrolyte and the separator. The all-solid-state ASCs also show the superior performance, such as high energy density of ∼14 Wh kg−1 and a power density of ∼3.6 kW kg−1.

2D and 3D Silica‐Template‐Derived MnO2 Electrocatalysts towards Enhanced Oxygen Evolution and Oxygen Reduction Activity

AbstractIn this work, a hard‐template‐based nano‐replication process is employed to prepare mesoporous MnO2 materials. We adopted four silica materials, namely, SBA‐15, KIT‐6, MCM‐41, and MCM‐48 as templates to prepare MnO2 materials by using a nanocasting route. The structural characteristics of the resultant MnO2 materials were thoroughly investigated by using XRD, BET, FESEM, HR‐TEM, XPS, and Raman techniques. All studies confirmed the replication of porous MnO2 nanostructures from silica supports in β‐crystallographic form. By employing X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS), we identified the existence of Mn and oxygen vacancies in the developed MnO2 material. The hydrodynamic linear sweep voltammetric technique was employed to demonstrate the efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity of the catalyst in 0.1 M KOH solution. The KIT‐6‐derived MnO2 nanostructure displayed equal activity to the benchmark catalyst RuO2. This work lays a foundation to prepare and employ ordered mesoporous MnO2 materials as OER/ORR catalysts, which have potential applications in electrochemical energy conversion and storage devices.

Hydrothermally synthesized porous Mn3O4 nanoparticles with enhanced electrochemical performance for supercapacitors

Porous like nanostructures are significant electrodes for electrochemical capacitors owing to their high surface area and variable pore sizes. In this study, an attempt was made to synthesize porous like Mn3O4 structure using H2O2 at different concentrations via solvent assisted hydrothermal method. The concentration of H2O2 during synthesis played critical role in controlling microstructure, morphology and hence supercapacitive performance. The XRD pattern shows, there is no much change in the diffraction peaks but peak broadening with addition of H2O2 was notified, which indicates decrease in crystallite size. The Raman studies also support the XRD result and the main Raman peak at 658 cm−1 shifted with increase in solvent concentration which is due to grain size effect. The SEM micrographs confirmed that the samples synthesized at 3 M H2O2 concentration are of porous like structure with variable pore sizes which is positive sign for supercapacitor applications. The electrical conductivity of the sample increased with temperature. The electrochemical properties of porous Mn3O4 were studied using CV, CP and EIS. The Mn3O4 exhibited a specific capacitance of 435 F g−1 at a scan rate of 1 mV s−1 with good rate capability and excellent capacitive retention.

Mn2O3@C yolk-shell nanocubes as lithium-storage anode with suppressed surface electrolyte decomposition

In order to improve cyclic stability and rate capability of Mn2O3 as lithium-storage anode for lithium ion batteries, we propose a novel configuration: porous Mn2O3 nanocubes encapsulated in carbon shell (Mn2O3@C). The porous structure provides space to buffer the volume change, while the surface carbon coating shell suppresses the electrolyte decomposition on Mn2O3 and enhances the electronic conductivity of the anode. This unique configuration and its improved electrochemical performances are demonstrated by detailed physical characterizations and electrochemical measurements. It is found that the resulting Mn2O3@C retains a high reversible and stable lithium-storage capacity of 996 mAh g−1 at 0.2C (1C = 1018 mA g−1) after 200 cycles, while only 269 mAh g−1 for the porous Mn2O3 nanocubes without surface carbon shell, and the Mn2O3@C possesses an excellent rate capability (299 mA h g−1 at 10C). This configuration provides not only Mn2O3 but also other metal oxides with great potential application in high energy density batteries.

Electrothermal regeneration by Joule heat effect on carbon cloth based MnO2 catalyst for long-term formaldehyde removal

Carbon-based materials (e.g., activated carbon) have been widely used as contaminant removal media due to their unique adsorption properties. However, some of their other characteristics, such as electrothermal properties, have been greatly ignored in the field of environmental remediation. Herein, a kind of carbon cloth (CC)-supported MnO2 composite (MnO2-CC) was prepared and investigated for catalytic oxidation of gaseous formaldehyde (HCHO) under the assistance of electric power. The MnO2-CC composite exhibited unique Joule heat property and could efficiently convert electrical energy into heat energy. The surface temperature of MnO2-CC composite could be increased to as high as 138 °C within 20 s when 8 V input voltage was imposed. In addition, porous MnO2 nanosheets dispersed uniformly on the surface of CC surface, forming a kind of hierarchical core-shell structure. The close contacted interface could reduce energy loss during heat transfer. As a result, the used MnO2-CC composite could exhibit long-term HCHO removal efficiency by highly effective electrothermal regeneration. This work represents a convenient and fast approach that allows direct utilization of electric power to accelerate the complete mineralization of HCHO. The in-situ fast electric heating process along with the uniform dispersion of porous MnO2 on CC make the MnO2-CC fabric an excellent material for indoor HCHO abatement.

Waste tissue papers templated highly porous Mn3O4 hollow microtubes prepared via biomorphic method for pseudocapacitor applications

The electrode materials with large surface area and high porosity are predominant to enable the energy storage properties of electrochemical supercapacitors. Herein, lab-waste tissue paper templated trimanganese tetroxide hollow microtubes (Mn3O4 HMTs) with high porosity on their walls were synthesized via a facile biomorphic method. Initially, aqueous manganese precursor was impregnated onto the surface of cellulose fibers by means of evaporation of water molecules. After thermal treatment under ambient atmosphere, the cellulose fibers were removed, which led to the formation of Mn3O4 HMTs. The morphology, crystallinity and surface area of the prepared Mn3O4 HMTs were examined by FE-SEM, XRD and BET analyses. When tested in aqueous alkaline electrolyte, the as-prepared Mn3O4 HMTs delivered a maximum specific capacitance of 51.7 F g−1 at the current density of 1 mA cm−2 with good rate capability of 64.6% at high current density of 10 mA cm−2, which is due to the high porosity that enables an effective penetration of electrolyte ions. After 2000 cycles, the porous Mn3O4 HMTs demonstrated good cycling stability of 57.1% at a current density of 5 mA cm−2. This facile method for the preparation of hollow structured materials could provide a deep insight into novel pseudocapacitive materials.

Three-dimensional spongy framework as superlyophilic, strongly absorbing, and electrocatalytic polysulfide reservoir layer for high-rate and long-cycling lithium-sulfur batteries

In the development of lithium-sulfur (Li-S) batteries, various approaches have been adopted to enhance the electronic conductivity of the sulfur cathode and alleviate the shuttle effect of polysulfides; however, the strategies providing efficient solutions are still limited. To further improve the electrochemical performance of Li-S batteries, in this work we propose a new strategy involving the incorporation of a three-dimensional functional spongy framework as polysulfide reservoir layer, with strong absorbability and electrocatalytic activity towards sulfur species. The spongy framework has a hierarchical architecture composed of highly conductive Ni foam/graphene/carbon nanotubes/MnO2 nanoflakes (NGCM). The strongly interconnected Ni foam, graphene, and carbon nanotubes of the NGCM sponge facilitate electron transfer during discharge/charge processes; moreover, the superlyophilic properties of the NGCM sponge ensure good wettability and interface contact with the Li-S electrolyte, and the porous MnO2 nanoflakes provide strong chemisorptive and electrocatalytic effects on polysulfides (as confirmed theoretically and experimentally). The NGCM sponge, serving as a polysulfide reservoir layer attached on a conventional sulfur-mixed carbon nanotubes (S/CNTs) cathode, can provide improved reversible capacity, rate capability (593 mAh·g–1 at 3.0 C), and cycling stability. In addition, the self-discharge rate is greatly reduced, owing to the efficient conservation of polysulfides in the NGCM spongy framework.

Synthesis of Pseudocapacitive Porous Metal Oxide Nanoclusters Anchored on Graphene for Aqueous Energy Storage Devices with High Energy Density and Long Cycling Stability along with Ultrafast Charging Capability

AbstractRealization of safe electrochemical energy storages with high energy density and long cycle life along with the high power density enabling fast charging is a major challenge. Here, a strategy to realize high‐performance aqueous energy storages using porous Mn3O4 (p‐MG) positive and porous Fe2O3 (p‐FG) negative electrodes, where granular nanoclusters composing nanoparticles are produced on graphene through lithiation‐induced conversion and the shortened ion diffusion lengths in p‐MG and p‐FG give fast charging rate and excellent cycle stability is reported. Furthermore, it is found from cyclic voltammetry curves and specific capacitances that porous metal oxide structures play mainly as redox reaction sites, while graphene structures provide electrical conductivity to active sites. Indeed, the full‐cell configuration of p‐MG and p‐FG in a hybrid capacitor exhibits a distinguished high energy density exceeding those of aqueous batteries, in addition to excellent capacity retention over 30 000 redox cycles and the energy density 2.5‐fold higher than that of its counterpart with pristine Mn3O4 and Fe2O3 nanocrystals. Additionally, this capacitor shows the high power density allowing ultrafast charging in that the full cells in series can be charged within several seconds by the rapid USB charger, thus outperforming those of typical aqueous batteries by about 100‐fold.

High‐Performance Reversible Aqueous Zn‐Ion Battery Based on Porous MnOx Nanorods Coated by MOF‐Derived N‐Doped Carbon

AbstractRechargeable aqueous zinc‐ion batteries (ZIBs) have been emerging as potential large‐scale energy storage devices due to their high energy density, low cost, high safety, and environmental friendliness. However, the commonly used cathode materials in ZIBs exhibit poor electrochemical performance, such as significant capacity fading during long‐term cycling and poor performance at high current rates, which significantly hinder the further development of ZIBs. Herein, a new and highly reversible Mn‐based cathode material with porous framework and N‐doping (MnOx@N‐C) is prepared through a metal–organic framework template strategy. Benefiting from the unique porous structure, conductive carbon network, and the synergetic effect of Zn2+ and Mn2+ in electrolyte, the MnOx@N‐C shows excellent cycling stability, good rate performance, and high reversibility for aqueous ZIBs. Specifically, it exhibits high capacity of 305 mAh g−1 after 600 cycles at 500 mA g−1 and maintains achievable capacity of 100 mAh g−1 at a quite high rate of 2000 mA g−1 with long‐term cycling of up to 1600 cycles, which are superior to most reported ZIB cathode materials. Furthermore, insight into the Zn‐storage mechanism in MnOx@N‐C is systematically studied and discussed via multiple analytical methods. This study opens new opportunities for designing low‐cost and high‐performance rechargeable aqueous ZIBs.

Fabrication and the electrochemical activation of network-like MnO2 nanoflakes as a flexible and large-area supercapacitor electrode

Porous network-like MnO2 thick films are successfully synthesized on a flexible stainless steel (SS) mesh using a simple and low-cost electrodeposition method followed by an electrochemical activation process. Morphology, chemical composition, and crystal structure of the prepared electrodes before and after the activation process are determined and compared by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The results show that the implementation of the electrochemical activation process does not change the chemical composition and crystal structure of the films, but it influences the surface morphology of the MnO2 thick layer to a flaky nanostructure. Based on the electrochemical data analysis, the maximum specific capacitance of 1400 mF (381 F g−1) and 3700 mF (352 F g−1) are measured for small (2.6 cm2) and large (10 cm2) surface area electrodes, respectively. In addition, a flexible symmetric MnO2//MnO2 solid-state supercapacitor shows a capacitance of 0.3 F with about 98% retention at different bending angles from 0 to 360°.

Fabrication of Coral-like Pd based Porous MnO2 Nanosheet Arrays on Nickel Foam for Methanol Electrooxidation

Direct methanol fuel cells (DMFCs) have been seen as one of the desirable power sources, and the performance always depends on the ability of electrode materials to oxidize methanol. In this work, ...

Porous LiMn2O4 Microspheres With Different Pore Size: Preparation and Application as Cathode Materials for Lithium Ion Batteries

Three types of LiMn2O4 (LMO) microspheres with different pore size are prepared by a facile method, using porous MnCO3–MnO2 and Mn2O3 microspheres as the self-supporting template, for lithium ion batteries (LIBs) cathode material. Briefly, Mn2O3 and MnO2 microspheres are heated in air at 600 °C for 10 h to synthesize porous Mn2O3 spheres. Then the mixture of as-prepared spherical Mn2O3 and LiNO3 is calcined to obtain the LMOs. The morphology and structure of LMOs are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption/desorption analyses. The result shows that the maximum pore diameters of LMOs are 17 nm, 19 nm, and 11 nm, respectively. All LMOs microspheres are composed of similar sized nanoparticles; however, the surface of these microspheres is strewed with dense tinier pores or sparse larger pores. Generally, the nanoparticles will reduce the path of Li+ ion diffusion and increases the reaction sites for lithium insertion/extraction. Moreover, the pores can provide buffer spaces for the volume changes during charge–discharge process. The electrochemical performances of LMOs are investigated and LMO2 exhibits extremely good electrochemical behavior, especially the rate capability. The as-prepared LMO2 delivers a discharge capacity of 124.3 mAh g−1 at 0.5 C, retaining 79.6 mAh g−1 even at 5 C. The LMO2 sample also shows good capacity retention of 96.9% after 100 cycles at 0.5 C.

3D Hierarchical Microballs Constructed by Intertwined MnO@N-doped Carbon Nanofibers towards Superior Lithium-Storage Properties.

MnO is a promising high-capacity anode material for lithium-ion batteries (LIBs), but pristine material suffers short cycle life and poor rate capability, thus hindering the practical application. In this work, a new type of porous MnO microballs stringed with N-doped porous carbon (3DHB-MnO@NC) with a well-connected hierarchical three-dimensional network structure was prepared by the facile self-template method. The 3DHB-MnO@NC electrode can effectively promote the ion/electron transfer and buffer the large volume change of electrode during the electrochemical reaction. As the anode for LIBs, the 3DHB-MnO@NC possesses outstanding cycling performance (1247.7 mA h g-1 after 90 cycles at 200 mA g-1 ) and good rate capabilities (949.6 mA h g-1 after 450 cycles at 1000 mA g-1 ). The facile self-template method of the prepared 3DHB-MnO@NC composite paves a new way for practical applications of MnO in high performance LIBs.