Mild Aqueous Electrolyte Research Articles

Electrochemical behavior of olivine-type LiMnPO4-based material in a mild aqueous electrolyte

Olivine-type pristine LiMnPO4 and nickel-substituted LiNi0.05Mn0.95PO4 electrode materials were synthesized via a sol–gel route, and characterized by X-ray diffraction (XRD), transmission electron microscopy, and X-ray fluorescence analysis techniques. Their electrochemical properties in 2 M Li2SO4 aqueous solution were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge methods. Furthermore, X-ray absorption near edge structure analysis and XRD technique were employed to study the structural change of the pristine LiMnPO4 during the first charge/discharge cycle and the first-stage repeated charge/discharge activation cycles (increase in discharge capacity with increasing cycle number). The LiMnPO4-based electrodes were found to undergo a first-stage activation process with gradual increase in discharge capacity prior to capacity degradation in the experimental condition. Partial nickel substitution for manganese in LiMnPO4 can enhance the charge transfer reaction kinetics, and thereby increase the specific capacity of the LiMnPO4-based electrode.

4 V class aqueous hybrid electrochemical capacitor with battery-like capacity

A new aqueous hybrid electrochemical capacitor consisting of a porous positive capacitive electrode and a water-stable multi-layered Li negative electrode is demonstrated. The new cell design affords cell voltages close to 4 V in a mild aqueous electrolyte. Application of a pseudocapacitive positive electrode with high specific charge results in specific energy comparable to present rechargeable batteries.

Nano-structured birnessite prepared by electrochemical activation of manganese(III)-based oxides for aqueous supercapacitors

Powdery Mn 3O 4 and Mn 2O 3 electrodes with carbon and binding polymer were electrochemically stimulated and activated by successive potential cycles in a mild aqueous electrolyte containing alkali sulfate. The activation of the manganese oxides is affected by the electrode material, milling treatment, potential region, and electrolyte solution. It is found that the ball-milled Mn 3O 4 electrode demonstrated the highest specific capacitance, 190 F g −1, in 1 mol dm −3 Na 2SO 4 aqueous solution due to the phase transition from Mn 3O 4 to electrochemically active birnessite, Na y MnO 2· nH 2O. The increase in capacitance originated from the formation of birnessite possessing highly porous morphology. The nano-structured birnessite demonstrated long cycle life of about 2000 cycles with acceptable capacitance retention of 190–160 F g −1. The birnessite was applied as positive electrode of the asymmetric electrochemical capacitor with activated carbon negative electrode in the mild aqueous solution.

Fabrication and capacitance of Ni2+–Fe3+ LDHs/MnO2 layered nanocomposite via an exfoliation/reassembling process

Abstract Ni 2+ –Fe 3+ layered double hydroxides (LDHs)/MnO 2 layered nanocomposite has been fabricated by using both layer-by-layer self-assembly method and flocculated technology, based on electrostatic interaction of positively charged Ni 2+ –Fe 3+ LDHs nanosheets and negatively charged MnO 2 nanosheets. Ultraviolet–visible spectroscopy is used to probe the dynamic growth of the multilayer film, exhibiting progressive enhancement of optical absorption due to the assembly of Ni 2+ –Fe 3+ LDHs nanosheets and MnO 2 nanosheets. The assembled Ni 2+ –Fe 3+ LDHs/MnO 2 nanocomposite has been characterized by XRD, SEM and TEM. The electrochemical property of the synthesized Ni 2+ –Fe 3+ LDHs/MnO 2 layered nanocomposite has been studied using cyclic voltammetry in a mild aqueous electrolyte. The Ni 2+ –Fe 3+ LDHs/MnO 2 nanocomposite exhibits a relative good capacitive behavior in a neutral electrolyte system, and its initial capacitance value is 104 F g −1 .

Preparation and Characterization of Self-Assembled Manganese Dioxide Thin Films

Thin films of manganese dioxide (MnO2) were prepared by self-assembly of MnO2nanoparticles directly unto nickel-coated poly(ethylene terephthalate) flexible films using the newly developed horizontal submersion process. The thickness of deposited thin films was controllable by the deposition duration. This horizontal submersion deposition process for thin-film deposition is relatively easy, simple, and cost effective. Effects of deposition duration and calcination temperatures on the microstructure and electrochemical properties of self-assembled MnO2thin films were investigated. Optimized MnO2thin films exhibited high charge capacity, good cycling reversibility, and stability in a mild aqueous electrolyte and are thus promising electrode materials for the fabrication of thin-film electrochemical capacitors.

Self-assembled manganese dioxide nanowires as electrode materials for electrochemical capacitors

The microstructure and morphology of sol–gel derived manganese dioxide (MnO 2) xerogels were affected by the synthesis conditions and post synthesis heat treatment. Manganese dioxide nanoparticles in sol that were dialyzed to more acidic pH (pH 5.7) value were observed to self-assemble into nanowires, whereas non-dialyzed sols remained nanoparticulate in nature. MnO 2 xerogels of disordered nanowire network exhibited comparatively higher porosity and BET surface areas. The electrochemical properties of both MnO 2 nanowire and nanoparticle thin-film electrodes were evaluated using cyclic voltammetry in a mild aqueous electrolyte (0.1 M Na 2SO 4). The charge capacities of MnO 2 nanowire-based thin-film electrodes were substantially higher (~ 800 F/g) than those of nanoparticulate thin-film electrodes (~ 700 F/g).

Electroless Deposition of Conformal Nanoscale Iron Oxide on Carbon Nanoarchitectures for Electrochemical Charge Storage

We describe a simple self-limiting electroless deposition process whereby conformal, nanoscale iron oxide (FeO(x)) coatings are generated at the interior and exterior surfaces of macroscopically thick ( approximately 90 microm) carbon nanofoam paper substrates via redox reaction with aqueous K(2)FeO(4). The resulting FeO(x)-carbon nanofoams are characterized as device-ready electrode structures for aqueous electrochemical capacitors and they demonstrate a 3-to-7 fold increase in charge-storage capacity relative to the native carbon nanofoam when cycled in a mild aqueous electrolyte (2.5 M Li(2)SO(4)), yielding mass-, volume-, and footprint-normalized capacitances of 84 F g(-1), 121 F cm(-3), and 0.85 F cm(-2), respectively, even at modest FeO(x) loadings (27 wt %). The additional charge-storage capacity arises from faradaic pseudocapacitance of the FeO(x) coating, delivering specific capacitance >300 F g(-1) normalized to the content of FeO(x) as FeOOH, as verified by electrochemical measurements and in situ X-ray absorption spectroscopy. The additional capacitance is electrochemically addressable within tens of seconds, a time scale of relevance for high-rate electrochemical charge storage. We also demonstrate that the addition of borate to buffer the Li(2)SO(4) electrolyte effectively suppresses the electrochemical dissolution of the FeO(x) coating, resulting in <20% capacitance fade over 1000 consecutive cycles.

Preparation and capacitive property of manganese oxide nanobelt bundles with birnessite-type structure

One-dimensional manganese oxide nanobelt bundles with layered structure have been synthesized by hydrothermally treating the precursor, K-type layered manganese oxide in a NaOH solution of 6.0 mol L −1 at 150 °C for 30 h. The obtained material is characterized by XRD, SEM, TEM and BET analysis. The manganese oxide nanobelt bundles are more than 50 μm long and 20–50 nm wide, and the specific surface area is about 160 m 2 g −1. The electrochemical property of the synthesized manganese oxide nanobelt bundles has been studied using cyclic voltammetry in a mild aqueous electrolyte. The manganese oxide nanobelt bundle exhibits good capacitive behavior and cycling stability in a neutral electrolyte system, and its initial capacitance value is 268 F g −1.

Nanoparticulate magnetite thin films as electrode materials for the fabrication of electrochemical capacitors

Magnetite nanoparticles in stable colloidal suspension were prepared by the co-precipitation method. Nanoparticulate magnetite thin films on supporting stainless steel plates were prepared by drop-coating followed by heat treatment under controlled conditions. The effects of calcination temperature and atmosphere on the microstructure and electrochemical properties of nanoparticulate magnetite thin films were investigated. Nanoparticulate magnetite thin films prepared under optimized conditions exhibited a specific capacitance value of 82 F/g in mild aqueous 1.0 M Na2SO4 solution. Due to their high charge capacity, good cycling reversibility, and stability in a mild aqueous electrolyte, nanoparticulate magnetite thin films appear to be promising electrode materials for the fabrication of electrochemical capacitors.

Fabrication of MnO 2-pillared layered manganese oxide through an exfoliation/reassembling and oxidation process

MnO 2-pillared layered manganese oxide has been first fabricated by a delamination/reassembling process followed by oxidation reaction and then by heat treatment. The structural evolution of MnO 2-pillared layered manganese oxide has been characterized by XRD, SEM, DSC-GTA, IR and N 2 adsorption-desorption. MnO 2-pillared layered manganese oxide shows a relative high thermal stability and mesoporous characteristic. The layered structure with a basal spacing of 0.66 nm could be maintained up to 400 °C. The electrochemical properties of the synthesized MnO 2-pillared layered manganese oxide have been studied using cyclic voltammetry in a mild aqueous electrolyte. Sample MnO 2–BirMO (300 °C) shows good capacitive behavior and cycling stability, and the specific capacitance value is 206 F g −1.

A Simple Template‐Free Strategy to Synthesize Nanoporous Manganese and Nickel Oxides with Narrow Pore Size Distribution, and Their Electrochemical Properties

AbstractA facile method has been developed to synthesize nanoporous manganese and nickel oxides with polyhedron particle morphologies, high surface areas and narrow pore distributions by controlled thermal decomposition of the oxalate precursors. This method can be extended to using other kinds of salt precursors to prepare a series of nanoporous metal oxides. The heating rate, calcination temperature and controlled particle size of the oxalate precursors are important factors to get well‐defined pore structures. XRD, TG‐DTA, TEM, SEM, XPS, wet chemical titration and N2 sorption isotherm techniques are employed for morphology and structure characterizations. High surface area microporous manganese oxide (283 m2 g−1) and mesoporous nickel oxide (179 m2 g−1) with narrow pore distribution at around 1.0 nm and 6.0 nm, respectively, are obtained. Especially, we can tune the pore size of manganese oxides from microscope to mesoscope by controlling the thermal procedure. Electrochemical properties of manganese and nickel oxides are studied by cyclic voltammetry measurements in a mild aqueous electrolyte, which shows a high specific capacitance of 309 F g−1 of microporous manganese oxide and a moderately high specific capacitance of 165 F g−1 of mesoporous NiO due to their nanoporous structure, presenting the promising candidates for super capacitors (SC).

Pseudocapacitive behaviors of nanostructured manganese dioxide/carbon nanotubes composite electrodes in mild aqueous electrolytes: effects of electrolytes and current collectors

Nanostructured MnO2/carbon nanotubes composite electrode material was prepared using the liquid-phase deposition reaction starting with potassium permanganate (KMnO4) and manganese acetate (Mn(Ac)2·4H2O) as the reactants and carbon nanotubes (CNTs) as the substrates. The structure and morphology of the material was characterized by X-ray diffraction, infrared spectroscopy, and transmission electron microscope techniques. The electrochemical properties of the nano-MnO2/CNTs composite electrode in 1 M LiAc and 1 M MgSO4 solutions and in 1 M RAc (R = Li, Na, and K)–1 M MgSO4 mixed solutions, respectively, were studied. Experimental results demonstrated that the specific capacitance and rate discharge ability of the nano-MnO2/CNTs composite electrode in 1 M LiAc–1 M MgSO4 mixed solution is superior to that in 1 M LiAc or 1 M MgSO4 solution. For the 1 M RAc (R = Li, Na, and K)–1 M MgSO4 mixed electrolytes, the specific capacitance of the composite electrode was found to be in the following order: LiAc > NaAc > KAc.

Templated synthesis of hierarchically porous manganese oxide with a crystalline nanorod framework and its high electrochemical performance

A simple approach has been developed to synthesize hierarchically porous MnO2 with a crystalline nanorod framework using mesoporous silica SBA-15 as a template, combined with in situ ion-exchange and surfactant-extraction processes without calcination. XRD, nitrogen adsorption analysis, FE-SEM, TEM, XPS and FT-IR techniques are used for the structural characterization. Such MnO2 materials show a macro–mesoporous hierarchical nanostructure containing large pores of several hundreds of nanometres and mesopores of 3.76 nm with a high surface area of 142 m2 g−1. The mesoporous framework of this material is composed of aligned single crystalline MnO2 nanorods of ca. 5–6 nm in diameter and ca. 20–25 nm in length. The electrochemical properties of the prepared MnO2 material were studied using cyclic voltammetry in a mild aqueous electrolyte, which shows that such a MnO2 nanostructure has a very high specific capacitance of 258 F g−1 and a good reversibility due to its favorable phase and hierarchically porous structure as well as high surface area.

Nanostructured MnO 2: Hydrothermal synthesis and electrochemical properties as a supercapacitor electrode material

The structural, morphological and electrochemical properties of the hydrothermally prepared manganese oxide (MnO 2) nanostructures are discussed in this paper. Interesting nanostructures of MnO 2, mixture of nanostructured surface with a distinct plate-like morphology and nanorods, have been prepared by employing hydrothermal synthesis under mild conditions. The specific surface area of the prepared material was 132 m 2 g −1. Electrochemical properties of the synthesized nanostructured material were studied using galvanostatic cycling and cyclic voltammetry in a mild aqueous electrolyte that showed a high specific capacitance of 168 Fg −1. In addition, the synthesized nanomaterial showed a good reversibility and cycling stability.

A Hybrid Activated Carbon-Manganese Dioxide Capacitor using a Mild Aqueous Electrolyte

A hybrid electrochemical capacitor using and activated carbon (AC) as positive and negative electrodes, respectively, has been designed. The electrodes were individually tested in a mild aqueous electrolyte (0.65 M in order to define the adequate balance of active material in the capacitor as well as the working voltage. The hybrid electrochemical capacitor was cycled between 0 and 2.2 V for over 10,000 constant current charge/discharge cycles. A real energy density of 10 Wh/kg was reproducibly measured with a real power density reaching 3600 W/kg. The hydrogen and oxygen evolution reactions on AC and electrodes, respectively, were investigated in 0.65 M Despite the good electrochemical performance of the 2.2 V capacitor, gas evolution could be a hindrance for practical use. Subsequently, a 1.5 V capacitor was tested for more than 23,000 cycles and yielded interesting electrochemical performance with negligible gas evolution. © 2004 The Electrochemical Society. All rights reserved.

A Hybrid Fe[sub 3]O[sub 4]-MnO[sub 2] Capacitor in Mild Aqueous Electrolyte

A hybrid electrochemical capacitor using MnO 2 and Fe 3 O 4 as active material for the positive and the negative electrode, respectively, has been designed. The electrodes have been individually tested in a mild aqueous electrolyte (0.1 M K 2 SO 4 ) to define the adequate balance of active material in the capacitor as well as the working voltage of a capacitor based on these two electrodes. The specific capacitances of MnO 2 and Fe 3 O 4 were 150 ′ 10 and 75 ′ 8 F/g, respectively whereas the specific capacitance of the Fe 3 O 4 /MnO 2 capacitor was equal to about 20 F/g of active material. The hybrid electrochemical capacitor has been cycled between 0 and 1.8 V for over 5000 constant current charge/discharge cycles. A real energy density of 7 Wh/kg was reproducibly measured with a real power density up to 820 W/kg.

Ideal Supercapacitor Behavior of Amorphous V2O5·nH2O in Potassium Chloride (KCl) Aqueous Solution

Amorphous a-V2O5·nH2O in mild KCl aqueous electrolyte proves to be an excellent electrode for a faradaic electrochemical capacitor. Cyclic voltammograms versus SCE give ideal capacitor behavior between 0.0 and +0.8 V at pH 6.67 and between −0.2 and +0.8 V at pH 2.32 with, respectively, a constant specific capacitance over 100 cycles of ca. 350 and 290 F/g, respectively. On short-circuit, a-V2O5·nH2O in 2 M KCl aqueous solution at pH 2.32 gave an initial current density of 0.28 A/cm2 and a total released charge of 4.5 C/cm2, which is to be compared with 0.32 A/cm2 and 11.1 C/cm2 for RuOOH·nH2O in 5.3 M H2SO4. Moreover, half the stored charge was released 1.6 times faster from the a-V2O5·nH2O electrode. These results demonstrate that the K+ ion can be used as the working ion in a faradaic capacitor, which frees the search for new materials from the constraint of working in a strong acid aqueous medium.

Orientational Dependence of Photoelectrochemical Etching in n ‐ GaAs

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Nanostructured Manganese Dioxide Thin Films prepared by a Novel Self-Assembly Process

We have reported herein a novel self-assembly horizontal submersion process for the deposition ofnanostructured manganese dioxide thin films on metalized plastic supporting substrates at ambient temperatureand pressure. Uniform manganese dioxide thin films were deposited directly onto metallized plastic supportingsubstrate via the spontaneous assembly of preformed manganese dioxide nanoparticles in the form of stablecolloidal suspension. This process affords a facile approach for the deposition of manganese dioxide thin filmsby simply repeating the submersion process after the prior deposited layer had been air-dried completely. Thinfilmdeposition process initially occurred through the spontaneous adsorption of manganese dioxidenanoparticles onto specific surface sites of the metalized substrate. Subsequent events of particle growth,clusters formation, and aggregation or self-organization of particle clusters eventually led to the deposition ofnanostructured thin films which were nanoparticulate and highly porous in nature. The surface morphologicalcharacteristics of deposited thin films were observed to be significantly affected by the duration of submersionand the post-deposition calcination temperature. By modulating and optimizing these parameters, thin films oftailored microstructure could therefore be prepared. Optimized manganese dioxide thin films were observed toexhibit excellent capacitive behavior as evidenced by the almost perfectly rectangular shape of cyclicvoltamograms within the potential range of 0.0 to 1.0 V (versus SCE) in mild aqueous Na2SO4 electrolyte. Thecycling stability and reversibility of these films were evaluated by prolonged charge-discharge cycling and nosubstantial deterioration of performance in terms of charge capacity and capacitive behaviors were observedafter 1000 cycles. We speculate that the high capacitance value exhibited by self-assembled manganese dioxidethin films in mild aqueous electrolyte could be attributed to reversible and homogenous intercalation anddeintercalation of protons during the charge and discharge cycling. The potential utility of self-assembledmanganese dioxide thin films for the fabrication of electrochemical devices, in particular thin-filmelectrochemical capacitors is therefore envisaged.