Mesoporous MnO2 Research Articles

2D mesoporous MnO2 nanosheets for high-energy asymmetric micro-supercapacitors in water-in-salt gel electrolyte

Two-dimensional (2D) mesoporous nanosheets as electrodes present a critical materials platform for dramatically boosting the performance of planar micro-supercapacitors (MSCs) due to their unique features of interconnected porous network, enriched nanopore arrays, and high specific surface area. However, efficient strategies for constructing such complicated mesoporous architectures are very limited. Here, we developed a supramolecular bottom-up self-assembly strategy for direct synthesis of ultrathin mesoporous manganese dioxide (m-MnO2) nanosheets for high-energy all-solid-state planar asymmetric MSCs (AMSCs). The m-MnO2 nanosheets exhibited ultrathin thickness of 10 nm, uniformly interconnected network of mesopores with size of 5–15 nm, high surface area of 128 m2 g−1, and remarkably enhanced capacitance of 243 F g−1 at 1 mV s−1 in comparison with non-mesoporous MnO2 nanosheets (123 F g−1). Further, all-solid-state AMSCs were assembled based on m-MnO2 nanosheets as positive electrode, porous VN nanosheets as negative electrode, and electrochemically exfoliated graphene as conductive agent and metal-free current collector in “water-in-salt” gel electrolyte. Importantly, our all-solid-state AMSCs operated stably at 2.0 V and offered impressive energy density of 21.6 mWh cm−3, outperforming most reported MnO2 based MSCs, and two times higher than lithium thin-film batteries (≤10 mWh cm−3). Also, they presented long-term cycling stability with 90% capacity retention after 5000 cycles, outstanding flexibility without observable capacitance decay under different bending angles, and facile serial and parallel interconnection for creating high-voltage and high-capacitance integrated bipolar cells. Therefore, our proposed strategy will open many opportunites for patterning novel 2D mesoporous metal oxide nanosheets for high-performance microscale electrochemical energy storage devices.

Mesoporous MnO2 hollow spheres for enhanced catalytic oxidation of formaldehyde

In this work, hollow MnO2 spheres were synthesized via a sacrificial templating method using SiO2 nanospheres as hard templates. The MnO2 coating on SiO2 was achieved by a newly devised low-temperature, controlled precipitation by redox (CPR) method which is based on the controlled redox reaction between KMnO4 and Mn(NO3)2 at 30 °C. After calcination of the SiO2@MnO2 core shell spheres at 300 °C, hollow spheres were obtained following template removal by NaOH etching. The hollow spheres were characterized by XRD, Raman spectroscopy, TEM, HRTEM, N2 adsorption, XPS and H2-TPR. Two different MnO2 crystal phases (γ- and δ-MnO2) could be obtained by making simple changes in the precursor addition protocols during synthesis. All the samples had high BET surface areas between 104 m2 g−1 and 236 m2 g−1, hierarchical pore size distribution with high mesoporosity and the presence of oxygen vacancies for high mobility of oxygen species on the catalyst surface. The catalysts were used for the complete catalytic oxidation of formaldehyde in dry air (100 ppmv; GHSV: 30,000 h−1). Long-term stability tests showed that γ-MnO2 deactivated gradually with time potentially due to structural collapse of the hollow spheres. The interlayer spacing in the δ-MnO2 sample, however, was responsible for increasing the expected conversion due to the regeneration of oxygen/hydroxyl species from adsorbed water formed from the oxidation of formaldehyde on the catalyst surface.

Incorporation of MnO2 into boron-enriched electrospun carbon nanofiber for electrochemical supercapacitors

MnO2- and boron-incorporated polyacrylonitrile (PAN)/pitch-based carbon nanofiber (PPBMn) composites for electrochemical supercapacitors are successfully fabricated by one-step electrospinning using a combined solution of MnCl2, B2O3, PAN, and pitch. The surface morphologies, microstructures, surface chemical states, and texture properties of the PPBMn composites are investigated and the effect of the MnCl2 content on the electrochemical performance in aqueous electrolytes is also examined. The PPBMn composites exhibit a high specific surface area with mesoporous structure, and boron and MnO2 functional groups as electroactive sites. Enriched boron and MnO2 functional groups provide low internal resistance of charge diffusion by better wettability of electrolyte ions into the pores and also accommodate more charges, leading to high gravimetric capacitance and energy density, and enhanced cycling stability. Therefore, the PPBMn series exhibits superior electrochemical performance through the combined functions of their double-layer capacitance and pseudo-capacitive character through the high porosity, higher attractive force by the surface chemical activity and the wettability between the electrode and electrolyte.

In Situ Synthesis of 1D Mesoporous MnO@C Nanorods for High Performance Li-Ion Batteries

Transition metal oxides have been regarded as the most potential anode material for lithium-ion batteries (LIBs), because of their high theoretical capacity, abundant resource, and low cost. Nevertheless, poor conductivity and large volumetric expansion during the charge–discharge processes make it difficult for LIBs application. In this work, we have adopted an in situ carbon coating method to synthesize 1D mesoporous MnO@C nanorods, which effectively work out the above problems of LIBs. Meanwhile, the MnO@C-3 (the mixture is 40 mL of H2O in solvothermal reaction) anode exhibits excellent rate capability with the capacity retention of 90.3% at 2.0 A g–1 and prominent cycling stability at 5.0 A g–1 with the discharge capacity of 1210.1 mAh g–1 after 400 cycles. When assembled to a full cell with commercial LiFePO4 as cathode, the full cell represents 360.7 mAh g–1 after 30 cycles (based on the anode), which displays a development potential for practical application.

Enhanced Performance and Conversion Pathway for Catalytic Ozonation of Methyl Mercaptan on Single-Atom Ag Deposited Three-Dimensional Ordered Mesoporous MnO2.

In this study, Ag deposited three-dimensional MnO2 porous hollow microspheres (Ag/MnO2 PHMSs) with high dispersion of the atom level Ag species are first prepared by a novel method of redox precipitation. Due to the highly efficient utilization of downsized Ag nanoparticles, the optimal 0.3% Ag/MnO2 PHMSs can completely degrade 70 ppm CH3SH within 600 s, much higher than that of MnO2 PHMSs (79%). Additionally, the catalyst retains long-term stability and can be regenerated to its initial activity through regeneration with ethanol and HCl. The results of characterization of Ag/MnO2 PHMSs and catalytic performance tests clearly demonstrate that the proper amount of Ag incorporation not only facilitates the chemi-adsorption but also induces more formation of vacancy oxygen (Ov) and lattice oxygen (OL) in MnO2 as well as Ag species as activation sites to collectively favor the catalytic ozonation of CH3SH. Ag/MnO2 PHMSs can efficiently transform CH3SH into CH3SAg/CH3S-SCH3 and then oxidize them into SO42- and CO2 as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy. Meanwhile, electron paramagnetic resonance and scavenger tests indicate that •OH and 1O2 are the primary reactive species rather than surface atomic oxygen species contributing to CH3SH removal over Ag/MnO2 PHMSs. This work presents an efficient catalyst of single atom Ag incorporated MnO2 PHMSs to control air pollution.

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.

Mesoporous Mn3O4 coated reduced graphene oxide for high-performance supercapacitor applications

We report the facile synthesis of mesoporous Mn3O4 coated reduced graphene oxide (rGO) nanocomposite using a simple low temperature wet chemical process and demonstrated the nanocomposite material as high-performance electrodes for electrochemical supercapacitor. The nanocomposite structure is unique as it consists of an ultra-thin, mesoporous (pore size ∼1.9–2.6 nm) with oriented pore size of Mn3O4 layer deposited on the surface of rGO. The structure and the orientation of nanopores in the Mn3O4 layer were further confirmed using HRTEM, while structural and morphological analysis were carried out using XRD, Raman spectroscopy, SEM, TEM, and SAED. The pore size and the pore distributions were verified using BET surface area technique, which demonstrated the nanocomposite exhibits uniform distribution of pores of dimension ∼1.9–2.6 nm throughout. The electrocatalytic behavior of the nanocomposite was found to be ideal for their use as supercapacitor electrodes as high-performance charge storage devices. Finally, we demonstrate the supercapacitor electrode using Mn3O4-rGO nanocomposite followed by their electrochemical characterizations for electrocatalytic activity for charge storage. The hybrid material shows best capacitance value of 221 F g−1 at current density 0.15 A g−1 with good cycling stability. We believe that our investigations will pave a pathway towards various new applications, including, electrochemical catalysis, sensing, energy harvesting and storage and many more.

Silica template assisted synthesis of ordered mesoporous β–MnO2 nanostructures and their performance evaluation as negative electrode in Li-ion batteries

In the pursuit of high capacity anode materials transition metal oxides have paid great deal of attention. However poor electronic conductivity, high discharge potential and volume change during electrochemical cycling hinders their practical applications. In this report, we synthesize the well-ordered mesoporous β-MnO2 phases (pyrolusite structure) using SBA-15 and MCM-48 templates. The product derived from SBA-15, designated as SBA-MnO2 has interconnected nanorod like morphology, whereas the product derived from MCM-48, designated as MCM-MnO2 exhibits open cage/bowl like morphology. The products are characterized by XRD, FTIR, FESEM, TEM, XPS, BET surface area measurements. Further, electrochemical studies are carried out to investigate their application as anode material for Li-ion batteries. Galvanostatic cycling shows initial discharge capacity of ∼1500 mAhg−1 and 1750 mAhg−1 respectively for SBA-MnO2 and MCM-MnO2. After 100 charge-discharge cycles, MCM-MnO2 electrode exhibits capacity ∼345 mAhg−1 and SBA-MnO2 shows a capacity of ∼245 mAhg−1. Though both the materials show capacity fading upon long cycling, their performance is better compared to other MnO2 nanostructures reported in the literature. They also exhibit good rate capability indicating that mesoporous MnO2 materials reported here can be potential candidate for Li-ion storage.

Mesoporous MnO2 fibers as an efficient bifunctional absorber for high-performance lithium-sulfur batteries

A novel morphology of mesoporous MnO2 fibers (MOF) are successfully prepared for the first time as host materials for lithium-sulfur (LiS) batteries. The as-prepared mesoporous MnO2 fibers can restrain the polysulfides dissolution via chemical bonding and physical trapping at the same time. As a result, the mesoporous MnO2 fibers sulfur (MOF/S) composites exhibit excellent cycle performance. The MOF/S composite electrodes deliver a high initial capacity of 1015 mAh g−1 and maintain 815 mAh g−1 after 200 cycles at 0.1 C.

Mesoporous MnO2 structured by ultrathin nanosheet as electrocatalyst for oxygen reduction reaction in air-cathode microbial fuel cell

In order to couple merits of two dimension and porous materials, by using unique solvent free method, the mesoporous layered α-MnO2 structured by 2 nm nanosheet was successfully synthesized, which possesses ultra-high surface area (339 m2 g−1), meso pore size of 6 nm and large amount of oxygen vacancies. When serving as a cathodic oxygen reduction reaction catalyst in microbial fuel cell, it exhibits superior electrocatalytic performance comparable to the commercial Pt/C and achieves the maximum power density of 1671 ± 26 mW m−2 with a exchange current density of 21.18 A cm−2. Meanwhile, density functional theory study reveals that the obviously shrinking of forbidden band and the pseudo band gap between two sharp peak of d DOS, which results in an excellent electrical conductivity, efficient electron transport and low overpotential of electrode. Therefore, it can be expected that the as-prepared MnO2 catalyst, with extraordinary electrocatalytic performance through a combination of the ultrathin nanosheet architecture and oxygen vacancies, is promising and produces high power density in microbial fuel cell.

Enhanced peroxymonosulfate activation for phenol degradation over MnO2 at pH 3.5-9.0 via Cu(II) substitution.

Cu(II) doped mesoporous MnO2 (Cu-MnO2) was prepared to establish an intimate functional link between the structure substitution and catalytic peroxymonosulfate (PMS) activation. Based on the characterization of powder X-ray diffraction (XRD), N2 adsorption-desorption measurement, scanning electron microscope (FE-SEM) and transmission electron microscope (TEM), Cu-MnO2 had a typical long range ordered mesoporous structure and Cu was successfully introduced in octahedral framework. It exhibited excellent catalytic activity and stability for the phenol degradation by PMS. Phenol was always efficiently degraded over Cu-MnO2 at a pH range of 3.5-9.0. For example, the reaction rate constant at pH 7.0 was 0.073 min-1, which was two times higher than that of MnO2 (0.039 min-1). Importantly, 1O2 was identified as the primary reactive species in Cu-MnO2/PMS system. X-ray photoelectron spectroscopy (XPS) confirmed that more exposed surface oxygen defects due to Cu doping were responsible to the enhancement of PMS activation for phenol degradation. The results of PMS decomposition and oxygen evolution indicated that surface oxygen defects lower the reaction energy barrier of PMS decomposition by generating 1O2 via the energy trapping by oxygen. Finally, the heterogeneous PMS activation mechanism over Cu-MnO2 was proposed.

Facile synthesis of mesoporous MnO2 nanosheet and microflower with efficient photocatalytic activities for organic dyes

MnO2 nanosheets and microflowers are prepared by a facile one-step hydrothermal method with a KMnO4-Na2SO4 aqueous solution system in this paper. Photocatalytic properties of the as-prepared products for different organic dyes are investigated under ultraviolet light and visible light irradiation at room temperature. The MnO2 nanostructures with mesoporous structures exhibit enhanced photocatalytic performance under UV light, the degradation efficiency up to 91.1% within 30 min for methylene blue and 89.8% for methyl orange within 120 min. Moreover, the possible mechanism of photocatalytic degradation for MB was proposed. MnO(OH) existing in the product provides more ˙OH during the degradation process, as well as influences the band gap of the product, which enhanced the separation of the photo-induced electron-hole pairs, thereby improved photocatalytic activity of MnO2 nanostructure. The results reveal that the as-prepared MnO2 nanostructures might have a potential application for organic contaminants degradation in water purification field.

Investigation of the Reaction Mechanism in Mesoporous MnO2 As Anode Material for Lithium Ion Batteries

Lithium ion batteries (LIBs) are the mostly used energy storage systems because of their high energy density and excellent cycle life. Recently, as the more expanding application fields of LIBs from portable devices to electric vehicle (EV) and energy storage system (ESS), the demands for better LIBs increase. Energy density is one of the most important required performances of batteries. A high energy density in batteries can be achieved by increasing the capacity of the electrodes or by increasing the working potential of the cathode materials. In the field of field of anode materials, research is underway to increase capacity, because the capacity of graphite widely used as anode in commercial LIBs is limited (~372mAh/g). Transition metal oxides such as CoO, Co3O4, NiO, FeO and Fe2O3 have attracted great attention due to their high theoretical capacity (700~1500 mAh/g) based on the conversion reaction mechanism. Mn-based oxides are the promising anode materials for lithium ion battery due to low cost, lower operating voltage compared to the Co, Ni, Fe and Cu based oxides and their high theoretical capacity (MnO : 756 mAh/g, Mn3O4 : 934 mAh/g, Mn2O3 : 1018 mAh/g, MnO2 : 1232 mAh/g). Many groups reported that nanostructured manganese oxides show higher capacity than theoretical capacity based on the conversion reaction mechanism. However, their exact reaction mechanisms are not yet clear and information about the reaction mechanism of MnO2 is more insufficient compared to other manganese oxide materials, MnO, Mn3O4 and Mn2O3 because they have focused on the synthesis method of materials to improve their electrochemical performances. Chen et al. reported that electron energy loss spectra (EELS) and selected area electron diffraction (SAED) results propose that MnO2 is only partially reduced to LiMn3O4, instead of being reduced to Mn [1]. Furthermore, Fang et al. reported that the LixMnO2 (X=0.96) and Li2MnO2 are observed by ex situ X-ray diffraction (XRD) but MnO is not observed until Li2MnO2 is fully reduced to metallic Mn and Li2O at 0V. From high resolution transmission electron microscopy (HRTEM), Mn is one of the end products of discharge to 0V, while MnO is the end product of recharge for MnO2 at 3.0V [2]. Recently, by cyclic voltammetry, MnO2 is reduced to Mn via MnO intermediate and the oxidation of Mn0 to Mn2+ and Mn2+ to Mn4+ occur during charge [3,4]. But cyclic voltammetry cannot provide obvious evidence of phase formation. In our report, to propose the detailed reaction mechanism of MnO2, we synthesize ordered mesoporous MnO2 and use synchrotron-based X-ray techniques, high resolution transmission electron microscopy (HRTEM) and electrochemical techniques. Our new proposed reaction mechanism suggest experimentally that, for the first time, the formation of the MnO intermediate during 1st discharge and the further oxidation of Mn2+ to higher oxidation state during charge are involved in the reaction mechanism of MnO2. Therefore, we provide a better understanding of the reaction mechanism of MnO2 anode for Li ion batteries. More details will be discussed in the meeting. Reference s : [1] C. Chen, N. Ding, L. Wang, Y. Yu, I. Lieberwirth, Journal of Power Sources. 189 (2009) 552–556 [2] X. Fang, X. Lu, X. Guo, Y. Mao, Y.-S. Hu, J. Wang, Z. Wang, F. Wu, H. Liu, L. Chen, Electrochemistry Communications. 12 (2010) 1520-1523 [3] M. Kundu, C.C. Albert Ng, D.Y. Petrovykh, L. Liu, Chem. Commun. 49 (2013) 8459-8461 [4] J. Chen, Y. Wang, X. He, S. Xu, M. Fang, X. Zhao, Y. Shang, Electrochimica Acta. 142 (2014) 152-156

Tumor Microenvironment‐Responsive Mesoporous MnO2‐Coated Upconversion Nanoplatform for Self‐Enhanced Tumor Theranostics

AbstractThe insufficient blood flow and oxygen supply in solid tumor cause hypoxia, which leads to low sensitivity of tumorous cells and thus causing poor treatment outcome. Here, mesoporous manganese dioxide (mMnO2) with ultrasensitive biodegradability in a tumor microenvironment (TME) is grown on upconversion photodynamic nanoparticles for not only TME‐enhanced bioimaging and drug release, but also for relieving tumor hypoxia, thereby markedly improving photodynamic therapy (PDT). In this nanoplatform, mesoporous silica coated upconversion nanoparticles (UCNPs@mSiO2) with covalently loaded chlorin e6 are obtained as near‐infrared light mediated PDT agents, and then a mMnO2 shell is grown via a facile ultrasonic way. Because of its unique mesoporous structure, the obtained nanoplatform postmodified with polyethylene glycol can load the chemotherapeutic drug of doxorubicin (DOX). When used for antitumor application, the mMnO2 degrades rapidly within the TME, releasing Mn2+ ions, which couple with trimodal (upconversion luminescence, computed tomography (CT), and magnetic resonance imaging) imaging of UCNPs to perform a self‐enhanced imaging. Significantly, the degradation of mMnO2 shell brings an efficient DOX release, and relieve tumor hypoxia by simultaneously inducing decomposition of tumor endogenous H2O2 and reduction of glutathione, thus achieving a highly potent chemo‐photodynamic therapy.

One-pot synthesis of pure phase Mn3O4 at room temperature and probing its long-term supercapacitive performance

Present work deals with one-pot synthesis of pure phase mesoporous Mn3O4 nanoparticles by novel, easy, and cost-effective method at ambient conditions and probing its long-term supercapacitive performance. The co-precipitation-routed submicron MnCO3 particles (cp-MnCO3) and commercially available MnCO3 (cm-MnCO3) have been used as the precursor materials in the synthesis procedure. The nanoparticles of cp-Mn3O4 synthesized using cp-MnCO3 exhibits specific capacitance (Cs) of 290 (± 5) F g−1 at a current rate of 0.5 A g−1, whereas cm-Mn3O4 obtained from the chemical conversion of cm-MnCO3 shows Cs value of 204 (± 5) F g−1 at identical current rate. The better electrochemical behavior of cp-Mn3O4 is ascribed to its hierarchical pore size distribution and lower diffusion resistance, which facilitates an easy electrolytic ionic diffusion in the sample. cp-Mn3O4 also exhibits smaller relaxation time constant (τo = 140 ms), which allows it to deliver stored energy quickly at high power. Additionally, cp-Mn3O4 exhibits 71% capacitance retention after 15,000 cycles, 25 W h kg−1 energy density, and 202 W kg−1 power density at a current rate of 0.5 A g−1. Further, ex-situ XRD analysis demonstrates that cp-Mn3O4 retains its crystal structure to some extent even after prolonged cycles.

Template free synthesize mesoporous manganese dioxides for water treatment

Mesoporous materials present infinite application prospect for their special pore structure and large specific surface area. However, the synthesis process of mesoporous transition metal oxides always needs a template such as mesoporous silica to create the porous structure, thus the synthesis technology became complicated and energy consumption. In this work, 3D mesoporous MnO2 microsphere have been successfully prepared by a facile and simple hydrothermal process through introducing a certain amount of Ni2+. A high specific surface area (426 m2/g) was realized due to the mesoporous and ultrathin nanosheets structure. Owing to the special pore structure and 3D morphology assembled with ultrathin nanosheets (∼4 nm). These 3D mesoporous MnO2 shows a high-efficiency catalytic activity contrast with commercial MnO2 and 1D MnO2 nanorods and displays admirable repeatability as well as structure stability in dye degradation.

Mesoporous Mn2O3 Nanoparticles Via Hydrothermal Process for Supercapacitor Applications

In recent year, Mn2O3 nanomaterials exhibit a high surface area, narrow pore size distribution, large pore volume, and high thermal stability. MnOx materials have shown promising candidates for active electrode materials for various electrochemical systems like fuel cells, supercapacitors etc., due to their high specific capacitance, low cost, abundance and environmentally benign nature. In this work, the mesoporous Mn2O3 nanoparticles (NPs) were synthesized by manganese acetate, citric acid and sodium hydroxide through hydrothermal process at 150 oC for 3h. The synthesized mesoporous Mn2O3 NPs were characterized in terms of their morphology, surface, crystalline, electrochemical and electrochemical properties. For supercapacitor applications, the synthesized mesoporous Mn2O3 NPs based electrode showed the excellent specific capacitance (Csp) of 460 Fg−1 through good electrocatalytic activity by observing good electrochemical properties in 6M KOH. Excellent Csp might be explained by the facts in improving the surface area, porous surface and uniformity, which might favor in generating large active sites and fast ionic transport over the good electrocatalytic surface of the Mn2O3 electrode. The fabricated supercapacitors exhibited good cycling stability after 1000 cycles by maintaining ~ 86% of initial Csp.

Effect of pore size in mesoporous MnO2 prepared by KIT-6 aged at different temperatures on ethanol catalytic oxidation

KIT-6 mesoporous silica aged at 40, 100, and 150 °C were used as hard templates to prepare different mesoporous MnO2 catalysts, marked as Mn-40, Mn-100, and Mn-150, respectively. The catalytic activities of these catalysts and the effect of pore sizes on ethanol catalytic oxidation were investigated. Mn-40, Mn-100, and Mn-150 have triple, double, and single pore systems, respectively. On decreasing the aging temperature of KIT-6, the pore sizes of KIT-6 decrease and that of mesoporous MnO2 catalysts increase. The pore sizes and catalytic activities increase in the order: Mn-40 >Mn-100 > Mn-150. Mn-40 catalyst has a higher TOF (0.11 s−1 at 120 °C) and the best catalytic activity for ethanol oxidation because of a bigger pore size with three pore systems with maximum distribution at 1.9, 3.4, and 6.6 nm, decrease in symmetry and degree of order, more surface lattice oxygen species, oxygen vacancies resulting from more Mn3+ ions, and better low-temperature reducibility.

Smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing phase change material for in-situ thermal management of supercapacitors

Phase change materials (PCMs) have been widely applied for thermal energy storage and thermoregulation. This paper reported a smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing n-docosane PCM for in-situ thermal management of supercapacitors. The microcapsules based on an n-docosane core and SiO2 shell were first synthesized through interfacial polycondensation, and then a mesoporous nanoflake-like MnO2 layer was fabricated onto the surface of SiO2 shell through template-directed self-assembly. The chemical compositions of the resultant microcapsules were confirmed by energy dispersive X-ray, X-ray photoelectron and Fourier-transform infrared spectroscopy, and their nanoflake-like hierarchical morphology and well-defined core–shell structure were identified by scanning and transmission electron microscopy. The mesoporous architecture of nanoflake-like MnO2 outer layer was determined by nitrogen adsorption–desorption isotherm. The obtained microcapsules exhibited high phase-change enthalpies, high encapsulation efficiency, good phase-change and anti-osmosis performance and an effective thermoregulation capability. Most of all, these microcapsules demonstrated a higher specific capacitance than traditional MnO2/SiO2 solid particles at operation temperatures higher than 45 °C due to in-situ thermal management by the n-docosane core. They not only achieved a high specific capacitance of 312.2F/g at 45 °C with a current density of 1.0 A/g due to the mesoporous architecture of MnO2 layer, but also presented a superior long-term cycling stability with high capacitance retention of 94.7% after 1000 charging/discharging cycles. With the above-mentioned superiorities, the microcapsules developed by this work will be a good candidate as an electrode material for supercapacitors. This study opens a new pathway for the development and applications of microencapsulated PCMs in the thermoregulatory electrode system of supercapacitors and Li-ions battery cells.

2D, 3D mesostructured silicas templated mesoporous manganese dioxide for selective catalytic reduction of NOx with NH3

Employing nanocasting method, mesoporous MnO2 catalysts with large specific surface area and regular pore structure were synthesized by using three different types of mesostructure silicas (KIT-6, SBA-15, MCM-41) as hard templates. The physical and chemical properties of the three different mesostructured manganese oxide materials were comparatively and systematically characterized by using XRD, FT-IR, N2 adsorption-desorption, TEM, NH3-TPD, H2-TPR, XPS. The NH3-SCR performance of the mesoporous MnO2 was also evaluated on SCR self-assembly device. It was discovered that the mesostructure of the template would influence the amount and the kind of acid site, the reduction ability and then influence the catalytic performance of the materials. Mesoporous MnO2 templated from KIT-6 exhibited better catalytic performance than other mesoporous MnO2, indicating that the mesostructure of the materials has significant influence on the NH3-SCR performance. The KIT-6 templated MnO2 could induce 100% NOx conservation ratio range from 75 °C to 275 °C and exhibit good resistance of SO2 and H2O.