High electro-catalytic graphite felt/Mn O2composite electrodes for vanadium redox flow batteries

A mild and simple synthesis process for large-scale vanadium redox flow batteries(VRFBs)energy storage systems is desirable.A graphite felt/Mn O_2(GF-MNO)composite electrode with excellent electrocatalytic activity towards VO~(2+)/VO_2~+redox couples in a VRFB was synthesized by a one-step hydrothermal process.The resulting GF-MNO electrodes possess improved electrochemical kinetic reversibility of the vanadium redox reactions compared to pristine GF electrodes,and the corresponding energy efficiency and discharge capacity at 150 m A cm~(-2)are increased by 12.5%and 40%,respectively.The discharge capacity is maintained at 4.8 A h L~(-1)at the ultrahigh current density of 250 m A cm~(-2).Above all,80%of the energy efficiency of the GF-MNO composite electrodes is retained after 120 charge-discharge cycles at 150 m A cm~(-2).Furthermore,these electrodes demonstrated that more evenly distributed catalytic active sites were obtained from the Mn O_2particles under acidic conditions.The proposed synthetic route is facile,and the raw materials are low cost and environmentally friendly.Therefore,these novel GF-MNO electrodes hold great promise in large-scale vanadium redox flow battery energy storage systems.     

EQCM study of redox properties of PEDOT/MnO<Subscript>2</Subscript> composite films in aqueous electrolytes

Electrochemical behavior of poly-3,4-ethylenedioxythiophene composites with manganese dioxide (PEDOT/MnO₂) has been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance at various component ratios and in different electrolyte solutions. The electrochemical formation of PEDOT film on the electrode surface and PEDOT/MnO₂ composite film during the electrochemical deposition of manganese dioxide into the polymer matrix was gravimetrically monitored. The mass of manganese dioxide deposited into PEDOT at different time of electrodeposition and apparent molar mass values of species involved into mass transfer during redox cycling of PEDOT/MnO₂ composites were evaluated. It was found that during the redox cycling of PEDOT/MnO₂ composite films with various MnO₂ content, the oppositely directed fluxes of counterions (anions and cations) occur, resulting in a change of the slope of linear parts of the Δf–E plots with changing the mass fraction of MnO₂ in the composite film.Rectangular shape of cyclic voltammograms of PEDOT/MnO₂ composites with different loadings of manganese dioxide was observed, which is characteristic of the pseudocapacitive behavior of the composite material. Specific capacity values of PEDOT/MnO₂ composites obtained from cyclic voltammograms were about 169 F g^?1. The specific capacity, related to the contribution of manganese dioxide component, was about 240 F g^?1.     

LiMO<Subscript>2</Subscript>@Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> positive-electrode material for high energy density lithium ion batteries

Li[Ni_1/3Co_1/3Mn_1/3]O₂ (NCM 111) is a promising alternative to LiCoO₂, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g^?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO₂ (R-3m, M?=?Ni, Co) and a shell of Li₂MnO₃ (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li⁺/Ni²⁺ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li_1.15Na_0.5(Ni_1/3Co_1/3)_core(Mn_1/3)_shellO₂ can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g^?1 at 20 mA g^?1, and retains 90 % of its discharge capacity at 100 mA g^?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.

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Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g^?1 for 10 cycles followed by 90 cycles at 100 mA g^?1

     

Facile and scalable fabrication of graphene/polypyrrole/MnO<Subscript>x</Subscript>/Cu(OH)<Subscript>2</Subscript> composite for high-performance supercapacitors

In this study, to improve the specific capacitance of graphene-based supercapacitor, novel quadri composite of G/PPy/MnO_x/Cu(OH)₂ was synthesized by using a facile and inexpensive route. First, a two-step method consisting of thermal decomposition and in situ oxidative polymerization was employed to fabricate graphene/polypyrrole/manganese oxide composites. Second, Cu(OH)₂ nanowires were deposited on Cu foil. Afterwards, for the electrochemical measurements, composite powders were deposited on Cu(OH)₂/Cu foil substrate as working electrodes. The synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. The XRD analysis revealed the formation of PPy/graphene, Mn₃O₄/graphene, and graphene/polypyrrole/MnO_x. In addition, the presence of polypyrrole and manganese oxides was confirmed using FT-IR and Raman spectroscopies. Graphene/polypyrrole/MnO_x/Cu(OH)₂ electrode showed the best electrochemical performance and exhibited the largest specific capacitance of approximately 370 F/g at the scan rate of 10 mV/s in 6 M KOH electrolyte. In addition, other electrochemical measurements (charge–discharge, EIS and cyclical performance) of the G/Cu(OH)₂, G/PPy/Cu(OH)₂, G/Mn₃O₄/Cu(OH)₂, and G/PPy/MnO_x/Cu(OH)₂ electrodes suggested that the G/PPy/MnO_x/Cu(OH)₂ composite electrode is promising materials for supercapacitor application.     

Investigations Ce Doped MnO<Subscript>2</Subscript>/rGO as High Performance Supercapacitors Material

The novel Ce doped MnO₂/rGO composite was fabricated by a simple two-step hydrothermal method reacted for different times. As results, the composite reacted for 1h exhibits better electrochemical performance and rate capacity, the capacitive retention is 85% from 130.44 F g^–1 for first cycle decrease to 111.11 F g^–1 after 1000 cycles at the current density of 1 A g^–1, and 14.7 W h kg^–1 of energy density. Moreover, the BET surface area is 243 m² g^–1, and the average pore size is 7.9 nm, which will be convenient for the quick transport and migration of electrolyte ions during the charge–discharge process, and further confirm good rate capability.     

Nafion/TiO<Subscript>2</Subscript> hybrid membrane fabricated via hydrothermal method for vanadium redox battery

To improve the performance of Nafion membrane as a separator in vanadium redox battery (VRB) system, a Nafion/TiO₂ hybrid membrane was fabricated by a hydrothermal method. The primary properties of this hybrid membrane were measured and compared with the Nafion membrane. The Nafion/TiO₂ hybrid membrane has a dramatic reduction in crossover of vanadium ions compared with the Nafion membrane. The results of scanning electron microscope, energy dispersive X-ray spectroscopy, and X-ray diffraction of the hybrid membrane revealed that the TiO₂ phase was formed in the bulk of the prepared membrane. Cell tests identified that the VRB with the Nafion/TiO₂ hybrid membrane presented a higher coulombic efficiency (CE) and energy efficiency (EE), and a lower self-discharge rate compared with that of the Nafion system. The CE and EE of the VRB with the hybrid membrane were 88.8% and 71.5% at 60 mA cm⁻², respectively, while those of the VRB with Nafion membrane were 86.3% and 69.7% at the same current density. Furthermore, cycling tests indicated that the Nafion/TiO₂ hybrid membrane can be applied in VRB system.     

Liquid-phase MnO<Subscript>2</Subscript>-modification of clinoptilolite

Formation mechanism of the MnO₂ phase in the reaction of heterogeneous synthesis between Mn²⁺ and MnO ₄ ^- ions on a solid aluminosilicate surface in aqueous solutions was studied. It was shown that, for lowsilica forms, the Mn²⁺ ion is oxidized by the MnO ₄ ^- ion uniformly across the grain depth to give the MnO₂ phase and manganese manganites. For high-silica materials, the MnO₂ phase is formed on the outer surface of grains, with the decomposition of the MnO ₄ ^- ion and formation of the MnO₂ phase and molecular oxygen. It was found that, for the clinoptilolite rock used as a solid support, the yield of the MnO₂ phase and its distribution over the particle volume depend on the penetration capacity of the MnO ₄ ^- ion into the porous structure of this rock, determined by its composition. It is shown that the amount of the MnO₂ phase grows with increasing concentration of the MnO ₄ ^- ion and treatment duration, with the phase thickness being 15–20 and 350–1050 μm for, respectively, high- and low-silica samples.     

A novel method to fabricate lithium-ion polymer batteries based on LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/NG electrodes

A novel method to fabricate lithium-ion polymer batteries (LiPBs) has been developed. The LiPBs was fabricated without microporous polyolefin separators, taking spinel lithium manganese oxide (LiMn₂O₄) and natural graphite (NG) as the electrodes. The thicknesses of the cathodes and the anodes are 190 and 110 μm, respectively. The NG anode was coated with a microporous composite polymer film (20 μm thick) which composed of polymer and ultrafine particles. The coating process was effective and simple to be used in practical application, and ensured the composite polymer film to act as a good separator in the LiPB. The LiPBs assembled with the coated NG anodes and pristine LiMn₂O₄ cathodes presented better electrochemical performances than liquid lithium-ion battery counterparts, proving that the microporous composite polymer film can improve the performance of the coated NG anode. In this paper, the spinel LiMn₂O₄/(coated)NG-based LiPBs exhibited high rate capability, compliant temperature reliability, and significantly, excellent cycling performance under the elevated temperature (55°C).     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li₃V₂(PO₄)₃. The carbon-coated Li₃V₂(PO₄)₃ with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li₃V₂(PO₄)₃ (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g^?1 at 0.1 C and 162.9 mAh g^?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Graphene/Nafion ink-impregnated graphite felt for both positive and negative sides of enhanced vanadium redox flow battery

Journal of Solid State Electrochemistry - Electrocatalysts have a key role in the reactions of vanadium redox flow batteries (VRFB). A practical immersion-drying method is used to decorate graphene...     

Mesoporous amorphous MnO<Subscript>2</Subscript> as electrode material for supercapacitor

A kind of novel mesoporous, electrochemical active material, amorphous MnO₂ has been synthesized by an improved reduction reaction and using supramolecular as template. The synthesized sample was characterized physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscope (TEM), and Brunauer–Emmett–Teller (BET) surface area measurement, respectively. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 2 mol/l KOH aqueous solution electrolyte. The results of BET and TEM analysis indicated that supramolecular template plays an important role in the process of big specific surface area mesoporous material forming. After sintering at 200 °C, the sample still remained an amorphous structure, and its specific capacitance reached 298.7 F/g and presented a very stable capacitance after 500 cycles. In addition, the electrochemical process, such as ion transfer and electrical condition, was also investigated with electrochemical impedance spectroscopy.     

Preparation and electrochemical properties of Li<Subscript>0.97</Subscript>Er<Subscript>0.01</Subscript>FePO<Subscript>4</Subscript>/C composite for lithium-ion batteries

Li_0.97Er_0.01FePO₄/C composite was prepared by solid-state reaction, using particle modification with amorphous carbon from the decomposition of glucose and lattice doping with supervalent cation Er³⁺. All samples were characterized by X-ray diffraction, scanning electron microscopy, multi-point Brunauer Emmett and Teller methodes. The electrochemical tests show Li_0.97Er_0.01FePO₄/C composite obtains the highest discharge specific capacity of 154 mAh g⁻¹ at C/10 rate and the best rate capability. Its specific capacity reaches 131 mAh g⁻¹ at 2C rate. Its capacity loss is only 14.9 % when the rate varies from C/10 to 2C.     

Synergistic effect of additives on electrochemical properties of MnO<Subscript>2</Subscript> cathode in aqueous rechargeable batteries

The synergistic effect of bismuth oxide (Bi₂O₃) + titanium disulphide (TiS₂) additives in different proportions into the MnO₂ cathode material is physically modified and tested in a Zn-MnO₂ battery with aqueous LiOH electrolyte. It is found that these foreign cations stabilized the MnO₂ structure upon multiple cycling and the synergistic effect between two additives enhanced the rechargeability. This class of additive modified MnO₂ may be of interest for high-energy density and safer batteries for applications such as electric vehicles. The cyclability of the material suitable for electric vehicle (EV) applications is established in this report. The incorporation of Bi₂O₃ (3 wt.%) and TiS₂ (2 wt.%) additives into the MnO₂ cathode was found to improve the cell performance, this is partly due to the suppression of proton insertion. The results on cyclic voltammetric and charge–discharge studies describing the redox mechanisms in LiOH electrolyte and the role of additives on those redox reactions are discussed and compared with that of traditional KOH electrolyte.     

Preparation and characterization of MnO<Subscript>2</Subscript>/MWCNTs-modified graphite electrode and its catalysis for oxygen reduction reaction (ORR)

Manganese dioxides were prepared onto multi-walled carbon nanotubes (MWCNTs) by cyclic voltammetry (CV). The obtained manganese oxide-MWCNTs (MnO₂/MWCNTs) samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and thermogravimetry (TG), respectively. The MnO₂/MWCNTs-modified graphite electrode was utilized in the electrochemical oxygen reduction reaction (ORR) and the enhanced oxygen reduction peak current strongly suggested that MnO₂/MWCNTs has catalysis for ORR when compared to the pure MnO₂ or MWCNTs. The catalysis mechanism of MnO₂/MWCNTs for ORR was also-discussed.     

Rational design of double-confined Mn<Subscript>2</Subscript>O<Subscript>3</Subscript>/S@Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocube cathodes for lithium-sulfur batteries

Due to the high specific capacities and environmental benignity, lithium-sulfur (Li-S) batteries have shown fascinating potential to replace the currently dominant Li-ion batteries to power portable electronics and electric vehicles. However, the shuttling effect caused by the dissolution of polysulfides seriously degrades their electrochemical performance. In this paper, Mn₂O₃ microcubes are fabricated to serve as the sulfur host, on top of which Al₂O₃ layers of 2 nm in thickness are deposited via atomic layer deposition (ALD) to form Mn₂O₃/S (MOS) @Al₂O₃ composite electrodes. The MOS@Al₂O₃ electrode delivers an excellent initial capacity of 1012.1 mAh g^?1 and a capacity retention of 78.6% after 200 cycles at 0.5 C, and its coulombic efficiency reaches nearly 99%, giving rise to much better performance than the neat MOS electrode. These findings demonstrate the double confinement effect of the composite electrode in that both the porous Mn₂O₃ structure and the atomic Al₂O₃ layer serve as the spacious host and the protection layer of sulfur active materials, respectively, for significantly improved electrochemical performance of the Li-S battery.     

Comparison of electrocatalytic characterization of Ti/Sb-SnO<Subscript>2</Subscript> and Ti/F-PbO<Subscript>2</Subscript> electrodes

Electrocatalytic oxidation is a promising process for degrading toxic and biorefractory organic pollutants in wastewater treatment. Selection of electrode materials is crucial for electrochemical oxidation process. In this study, Ti/F-PbO₂ and Ti/Sb-SnO₂ electrodes were chosen to compare their electrocatalytic characterization, which were prepared by electrodeposition and thermal decomposition method, respectively. The surface morphology and crystal structure of two electrodes were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The linear polarization curves show that Ti/Sb-SnO₂ electrodes possess higher oxygen evolution overpotential than Ti/F-PbO₂ electrodes. But the stability and corrosion resistance ability of Ti/F-PbO₂ electrode was higher than that of Ti/Sb-SnO₂ electrode. The electrocatalytic activity of Ti/F-PbO₂ and Ti/Sb-SnO₂ electrodes was examined for the electrochemical oxidation of malachite green (MG). The bulk electrolysis shows that the Ti/Sb-SnO₂ electrodes exhibit the higher electrocatalytic activity for the degradation of MG than Ti/F-PbO₂ electrodes, and the degradation process is good fitting for the pseudo-first order reaction. The higher electrocatalytic activity of Ti/Sb-SnO₂ electrodes can be attributed to the higher oxygen evolution overpotential.     

Imprinted Azorubine electrochemical sensor based upon composition of MnO<Subscript>2</Subscript> and 1-naphthylamine on graphite nanopowder

A new sensitive and selective molecularly imprinted electrochemical sensor was developed for Azorubine determination. This sensor was based on molecularly imprinted polymer composed of poly(1-naphthylamine), triphenylamine (as cross-linkers) and dispersed MnO₂ nanorod particles on graphite nanopowders. The structure of the prepared nanocomposite was characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. Calibration curve of the imprinted sensor was linear in the concentration range 1–12 mg L^??1 with a detection limit of 0.57 mg L^??1. The application of the sensor was checked by the determination of Azorubine in a water sample.     

MnO<Subscript>2</Subscript> Nanoparticles and Carbon Nanofibers Nanocomposites with High Sensing Performance Toward Glucose

By combining the advantages of manganese dioxide nanoparticles (MnO₂ NPs) and carbon nanofibers (CNFs), a biosensing electrode surface as a high-performance enzyme biosensor is designed in this work. MnO₂ NPs and CNFs nanocomposites (MnO₂–CNFs) were prepared by using a simple hydrothermal method and then were characterized by scanning electron microscopy, powder X-ray diffraction, fourier transform infrared spectroscopy, energy dispersive spectrometry and electrochemisty. The results showed that MnO₂ NPs are uniformly attached to the surface of CNFs. Meanwhile, the MnO₂–CNFs nanocomposites as a supporting matrix can provide an efficient and advantageous platform for electrochemical sensing applications. On the basis of the improved sensitivity of MnO₂–CNFs modified electrode toward H₂O₂ at low overpotential, a MnO₂–CNFs based glucose biosensor was fabricated by monitoring H₂O₂ produced by an enzymatic reaction between glucose oxidase and glucose. The constructed biosensor exhibited a linear calibration graph for glucose in a concentration range of 0.08–4.6 mM and a low detection limit of 0.015 mM. In addition, the biosensor showed other excellent characteristics, such as high sensitivity and selectivity, short response time, and the relative low apparent Michaelis–Menten constant. Analysis of human urine spiked with glucose at different concentration levels yielded recoveries between 101.0 and 104.8%.