Pulse deposition of large area,patterned manganese oxide nanowires in variable aspect ratios without templates

Manganese oxide nanowires with β-MnOOH in core and Mn₃O₄ in shell were successfully plated onto various conductive substrates from a Mn(CH₃COO)₂ solution by anodic deposition under a two-electrode, pulse-rest mode. The aspect ratio of uniform nanowire morphologies in cm² scale is controllable by varying the deposition variables. Patterned MnO_x nanowire arrays were obtained by combining lithographic and electroplating techniques demonstrated to be a powerful method for preparing MnO_x nanowires in the field emission (FE) array cathodes with a low turn-on voltage (∼3.4 V/μm at 1 μA/cm²).     

Charge storage mechanism of MnO2 cathodes in Zn/MnO2 batteries using ionic liquid-based gel polymer electrolytes

Cathode reactions in Zn/MnO₂ batteries using aqueous electrolytes have been usually interpreted by the reduction of Mn^4 + to Mn^3 + while protons and/or cations penetrate inside the cathode. However, until now, the MnO₂ storage charge mechanism using a non-aqueous gel polymer electrolyte (GPE) has not been investigated. In this work, ionic liquid-based GPEs including BMIM Tf and ZnTf₂ have been employed in Zn/MnO₂ batteries. Different states of charge of MnO₂ cathodes used in Zn/IL-GPE/MnO₂ batteries have been analyzed by XPS and EDX techniques. XPS analysis showed that Mn^4 + is reduced during the discharge process at the same time as Zn^2 + cations are incorporated into the cathode. Besides, Zn^2 + cations insertion is accompanied by triflate anions.     

Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Electrochemical properties of Li(Li(1−x)/3CoxMn(2−2x)/3)O2 (0 ⩽ x ⩽ 1) solid solutions prepared by poly-vinyl alcohol (PVA) method

The whole range of solid solutions Li(Li_(1−x)/3Co_xMn_(2−2x)/3)O₂ (0 ⩽ x ⩽ 1) was firstly synthesized by an aqueous solution method using poly-vinyl alcohol as a synthetic agent to investigate their structure and electrochemical properties. X-ray diffraction results indicated that the synthesized solid solutions showed a single phase without any detectable impurity phase and have a hexagonal structure with some additional peaks caused by monoclinic distortion, especially in the solid solutions with a low Co amount. In the electrochemical examination, the solid solutions in the range between 0.2 ⩽ x ⩽ 0.9 showed higher discharge capacity and better cyclability than LiCoO₂ (x = 1) on cycling between 2.0 and 4.6 V with 100 mA g⁻¹ at 25 °C. For example, Li(Li_0.2Co_0.4Mn_0.4)O₂ (x = 0.4) exhibited a high discharge capacity of 180 mA h g⁻¹ at the 50th cycle. By synthesizing the solid solution between Li₂MnO₃ and LiCoO₂, the electrochemical properties of the end members were improved.     

A binder-free thin film anode composed of Co2 +-intercalated buserite grown on carbon cloth for oxygen evolution reaction

We present a binder-free catalytic anode for highly efficient and stable oxygen evolution reaction in alkaline media. The catalyst consists of a thin film of buserite-type layered manganese dioxide (MnO₂) intercalated with Co^2 + ions, resulting from electrodeposition of the layered MnO₂ film with tetrabutylammonium (Bu₄N⁺) ions on a carbon cloth, followed by ion-exchange of the initially incorporated Bu₄N⁺ with Co^2 + in solution. The electrode is capable to produce a current density of 10 mA cm^− 2 at an overpotential (η) of 377 mV with a Tafel slope of 48 mV dec^− 1, much superior to the layered MnO₂ without Co^2 +.     

Structural and magnetic properties of orthorhombic LixMnO2

Rietveld refinement of the crystal and magnetic structures of Li_xMnO₂ (x = 0.98, 1.00, 1.02) are performed using neutron and X-ray measurements. A significant structural disorder due to the presence of manganese ions in lithium positions (Mn_Li) and lithium ions in manganese ones (Li_Mn) is found to be a common feature of Li_0.98MnO₂, Li_1.00MnO₂, and Li_1.02MnO₂.An essential anisotropy of the thermal-expansion coefficients of the lithium manganese oxides is observed in the temperature range of 1.5–300 K. Furthermore, the distortion of the oxygen octahedral environment around the manganese ions decreases when the temperature lowers. This is attributed to the strong exchange interactions between parallel exchange-coupled Mn chains. First-principles calculations of the effective exchange-interaction parameters in Li₁₆Mn₁₆O₃₂ confirm the essential antiferromagnetic interactions between the chains. In addition, a hypothetical (Li₁₅Mn)Mn₁₆O₃₂ structure where a lithium atom located between the Mn double layers is replaced by a manganese atom is considered. The calculations reveal that the presence of such defects results in appearance of a ferromagnetic component that agrees with the magnetic measurements.     

Choline biosensors based on a bi-electrocatalytic property of MnO2 nanoparticles modified electrodes to H2O2

An interesting mode of reactivity of MnO₂ nanoparticles modified electrode in the presence of H₂O₂ is reported. The MnO₂ nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H₂O₂. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO₂ nanoparticles onto a glassy carbon (GC) electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0 × 10⁻⁵ –2.1 × 10⁻³ M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed.     

Electrochemical and XPS studies of a Nb-containing Ti-based glass-forming alloy system in H2SO4 solution

The corrosion behaviors of Ti₄₀Zr₂₅Ni_12 -xNb_xCu₃Be₂₀ (x = 0, 4, 8, and 12 at.%) alloys in 0.5 mol/L H₂SO₄ solution were studied, aiming to establish the relationship between Nb content and corrosion resistance. The addition of Nb element gives rise to a clear microstructural evolution, from a completely amorphous structure for the alloys without Nb and with 4% Nb alloys to an amorphous/crystalline composite structure for the alloys with 8% and 12% Nb. The alloy with higher Nb content exhibits better corrosion resistance, which can be attributed to the formation of Ti^4 +-, Zr^4 +-, and Nb^5 +-enriched highly protective surface film in corrosive solutions.     

MnO2 multilayer nanosheet clusters evolved from monolayer nanosheets and their predominant electrochemical properties

MnO₂ multilayer nanosheet clusters were prepared via electrochemical deposition route, which shows simpleness and high efficiency. The growth process of MnO₂ multilayer nanosheet clusters was investigated in this paper. The deposited MnO₂ films were characterized by XRD, SEM, TEM, and XPS. In addition, it was also electrochemically characterized by cyclic voltammetry in 1.0 M Na₂SO₄ electrolyte. The MnO₂ multilayer nanosheet clusters show a big specific capacitance, and it can be achieved about 521.5 F g^?1 at 5 mV s^?1. These materials also have a high electrochemical stability.     

Synthesis and characterization of hierarchically structured mesoporous MnO2 and Mn2O3

Hierarchically structured mesoporous MnO₂ with high surface area was prepared by a facile precursor route. Well-defined morphological manganese oxalate, synthesized by adding l-lysine via a hydrothermal method, was used as precursor. Mesoporous amorphous MnO₂ with high Brunauer–Emmett–Teller (BET) surface area (340 m²/g) and mesoporous Mn₂O₃ composed of nano-crystals (BET surface area 188 m²/g) were obtained by selective calcination of the oxalate precursor at 330 °C and 400 °C, respectively. Thermogravimetric and differential thermal analyses (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂-sorption analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and property of products. Cyclic voltammetry (CV) and charge–discharge measurements were used to preliminarily study the electrochemical performance of the products. The range of pH value (about 5.0–7.0) in the synthesis process is apt to prepare the hierarchical structured manganese dioxide. Other types of amino acids were also employed as the crystallization modifiers and different morphologies of manganese dioxides were obtained.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

First principles study of structure and properties of La- and Mn-modified BiFeO3

First principles calculations have been performed to study the effects of the La³⁺ and Mn³⁺ substitutions in the multiferroic BiFeO₃. The real compositions Bi_1−xLa_xFeO₃ and BiFe_1−xMn_xO₃ with x = 0.0, 0.1, 0.2, 0.3 were modeled by substitution of one, two and three Bi³⁺ or Fe³⁺ by La³⁺ or Mn³⁺ in the orthorhombic BiFeO₃ structure, respectively. Density functional theory within the generalized gradient approximation with Hubbard correction of Dudarev (GGA + U) and plane wave pseudo-potential approach has been used to track the changes that occur in the structural parameters, electronic structure, magnetic, optical and polarization properties of the modified BiFeO₃. The substitution of one Bi³⁺ with La³⁺ increases the band gap energy whereas the augmentation of La³⁺ substitutes decreases it. The substitutions of Fe³⁺ with Mn³⁺ do not change the band gap energy. The calculations predicted larger polarization of the modified BiFeO₃, antiferromagnetism for Bi_1−xLa_xFeO₃ and small ferrimagnetism for BiFe_1−xMn_xO₃. Better multiferroic properties are expected for BiFe_1−xMn_xO₃ materials (x = 0.1, 0.2) due to the increasing polarization and ferrimagnetic behavior. The optical properties were estimated by the calculated imaginary and real parts of the dielectric function. The increase of La³⁺ and Mn³⁺ substitutes lead to lower absorption intensity at energy range 2–7 eV.     

A novel solution for cathodic deposition of porous TiO2 films

The redox reaction between TiCl₃ and NaNO₃ to form Ti(IV) and NO₂^? prior to deposition in a specially designed TiCl₃ + NaNO₃ solution is the key step effectively promoting the cathodic deposition of porous TiO₂ films. The continuous reduction of NO₂^? to N₂ and NH₃ generates extensive OH^?, enhancing the deposition rate of TiO₂. The linear sweep voltammetric (LSV) and electrochemical quartz crystal microbalance (EQCM) studies reveal the electrocatalytic effect of oxy-hydroxyl-titanium already deposited onto the substrate for the NO₂^? and N₂ reduction. The porous and crystalline structures of as-deposited and annealed TiO₂ films are examined by field-emission scanning electron microscopic (FE-SEM), transmission electron microscopic (TEM) and selected area electron diffraction (SAED) analyses.     

Synthesis,crystal structure,and magnetic properties of K4Mn3(HPO4)4(H2PO4)2

A new layered compound, K₄Mn₃(HPO₄)₄(H₂PO₄)₂ (1), has been synthesized under hydrothermal conditions. It crystallizes in the monoclinic space group P2₁/n with a = 8.874(2) Å, b = 6.554(1) Å, c = 18.075(4) Å, and β = 93.39(3)°. The structure consists of zigzag [Mn₃O₁₄]_n chains of edge-sharing MnO₆ octahedrons and MnO₇ pentagonal bi-pyramids, which form layers of formula [Mn₃(HPO₄)₄(H₂PO₄)₂]^4? in the ab plane via H₂PO₄ and HPO₄ units with vertex-sharing. Potassium ions lie between these layers. Magnetic measurements indicate Curie–Weiss behavior above 6 K for 1. A Heisenberg model, with alternating exchange interactions J₁J₁J₂… within the chain and exchange interactions J₃J₃… between the chains, is proposed to describe the magnetic behavior.     

Ferromagnetic to spin glass cross over in (La,Tb)2/3Ca1/3MnO3

In the series La_2/3?xTb_xCa_1/3MnO₃, it is known that the compositions are ferromagnetic for smaller values of x and show spin glass characteristics at larger values of x. Our studies on the magnetic properties of various compositions in the La_2/3?xTb_xCa_1/3MnO₃ series show that the cross over from ferromagnetic to spin glass region takes place above x ≈ 1/8. Also, a low temperature anomaly at 30 K, observed in the ac susceptibility curves, disappears for compositions above this critical value of x. A mixed phase region coexists in the narrow compositional range 0.1 ≤ x ≤ 0.125, indicating that the ferromagnetic to spin glass cross over is not abrupt.     

Superabsorbent polymer binder for achieving MnO2 supercapacitors of greatly enhanced capacitance density

One common dilemma encountered in designing a supercapacitor electrode is that the specific capacitance (C_s) of the active material decreases significantly as the active-material loading (mass area^? 1) increases. As a result, the geometric capacitance density (GCD; Farad area^? 1) of the electrode does not scale up linearly but gradually levels off with increasing loading. For MnO₂ supercapacitors, this problem has been solved to a great extent by introducing a superabsorbent polymer (SAP) binder, namely polyacrylic acid (PAA), to form composite particles with MnO₂. Other than acting as a binder to bound together MnO₂ particles, the SAP is believed to facilitate distribution of electrolyte throughout the active layer owing to its electrolyte-absorbing and swelling behaviors. The C_s of MnO₂ remains almost unchanged as the oxide loading varies over a wide range (1.5–6.5 mg cm^? 2) of heavy active-material loading. In addition, putting PAA throughout the entire active layer helps to magnify the specific interaction between PAA and MnO₂ that is known to enhance the capacitance of individual MnO₂ particles. The success in combining both high C_s and high active-material loading results in GCD of ca. 1.8–1.4 F cm^? 2 even under very high current densities (ca. 35–260 mA cm^? 2 or 5–40 A g^? 1-MnO₂).     

Novel core–shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs

Novel core–shell SDC (Ce_0.8Sm_0.2O_1.9)/amorphous Na₂CO₃ nanocomposite was prepared for the first time. The core–shell nanocomposite particles are smaller than 100 nm with amorphous Na₂CO₃ shell of 4–6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm⁻¹. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm⁻² at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as ‘superionic highway’ in two-phase materials based on coated SDC.     

Electrode reactions of manganese oxides for secondary lithium batteries

Nanorods of MnO₂, Mn₃O₄, Mn₂O₃ and MnO are synthesized by hydrothermal reactions and subsequent annealing. It is shown that though different oxides experience distinct phase transition processes in the initial discharge, metallic Mn and Li₂O are the end products of discharge, while MnO is the end product of recharge for all these oxides between 0.0 and 3.0 V vs. Li⁺/Li. Of these 4 manganese oxides, MnO is believed the most promising anode material for lithium ion batteries while MnO₂ is the most promising cathode material for secondary lithium batteries.     

Novel method for the preparation of carbon supported nano-sized amorphous ruthenium oxides for supercapacitors

Nanostructured amorphous RuO₂ · xH₂O/C composite materials are prepared via a modified sol–gel process using glycolic acid. The glycolate anion, which dissociates from glycolic acid at pH 7, behaves as a stabilizer by adsorbing onto the RuO₂ · xH₂O surface, thus resulting in particles with a size of about 2 nm. As evidenced by zeta potential measurements, the surface charge of RuO₂ · xH₂O becomes more electronegative as the amount of glycolic acid increases. After heat treatment at 160 ^oC to remove the stabilizer, RuO₂ · xH₂O/C is found to exhibit an amorphous structure. The specific capacitance of RuO₂ · xH₂O/C particles (40 wt% Ru) prepared in the presence of glycolic acid (0.3 g L⁻¹) is 462 F g⁻¹, which is 30% higher than that of the material prepared in the absence of glycolic acid. Both the nanosized particles and the amorphous structure mainly contribute to this increase in the specific capacitance.     

Electrodeposition of MnO2 nanowires on carbon nanotube paper as free-standing,flexible electrode for supercapacitors

MnO₂ nanowires were electrodeposited onto carbon nanotube (CNT) paper by a cyclic voltammetric technique. The as-prepared MnO₂ nanowire/CNT composite paper (MNCCP) can be used as a flexible electrode for electrochemical supercapacitors. Electrochemical measurements showed that the MNCCP electrode displayed specific capacitances as high as 167.5 F g⁻¹ at a current density of 77 mA g⁻¹. After 3000 cycles, the composite paper can retain more than 88% of initial capacitance, showing good cyclability. The CNT paper in the composite acted as a good conductive and active substrate for flexible electrodes in supercapacitors, and the nanowire structure of the MnO₂ could facilitate the contact of the electrolyte with the active materials, and thus increase the capacitance.