Potentiodynamical deposition of nanosized manganese oxides as high capacitance electrochemical capacitors

Nanosized manganese oxides powders were potentiodynamically deposition onto the Pb substrates by anodic oxidation in 0.5 mol L⁻¹ MnSO₄ and 0.5 mol L⁻¹ H₂SO₄ mixed solution at 40 °C. The chemical composition of the sample was determined by complex titration with ethylene diamine tetraacetic acid and redox titration. X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and chronopotentiometry were employed to characterize the materials. The highest specific capacitance of the MnO_x composite electrode was up to 420 F g⁻¹ in 1.0 mol L⁻¹ Na₂SO₄ electrolyte at the scan rate 5 mV s⁻¹. The synthesized nanosized manganese oxide exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.     

Preparation and characteristics of nanostructured MnO2/MWCNTs using microwave irradiation method

Ball-nanostructured MnO₂/MWCNTs composite was successfully prepared by microwave irradiation. The surface morphology and structures of the composite were examined by scanning electron microscope and X-ray diffraction. Multi-walled carbon nanotubes play a role as sustainment to inhibit MnO₂ nanoplates from collapsing into nanorods. The electrochemical studies indicated that the composite had ideal capacitive performance and high specific capacitances of 298 F g^− 1, 213 F g^− 1 and 198 F g^− 1 at the current density of 2 mA·cm^− 2, 10 mA·cm^− 2 and 20 mA·cm^− 2, respectively. The formation mechanism of nanostructured MnO₂/MWCNTs and the electrochemical behaviour of composites were discussed in detail.     

A new asymmetric supercapacitor based on λ-MnO2 and activated carbon electrodes

Lithium-ion intercalated compound λ-MnO₂ was used as positive electrode in asymmetric supercapacitor with activated carbon used as negative electrode in 1 mol L^− 1 Li₂SO₄ aqueous electrolyte solution. Phase composition, morphology and particle sizes of λ-MnO₂ were studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical capacitive performance of the asymmetric supercapacitor was tested by cyclic voltammetry and galvanostatic charge-discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within wide potential range of 0-2.2 V. The specific capacitance is 53 F g^− 1 at a constant current density of 10 mA cm^− 2. The energy density is 36 W h kg^− 1 with a power density of 314 W kg^− 1. It is obvious that λ-MnO₂ is a potential electrode material for asymmetric supercapacitor.     

A voltammetric and nanogravimetric study of ZnSe electrodeposition from an acid bath containing Zn(II) and Se(IV)

The negative potential sweep of a polycrystalline Au electrode in a solution containing 5 × 10^− 4 mol L^− 1 SeO₂, 0.2 mol L^− 1 Zn(ClO₄)₂ and 0.5 mol L^− 1 HClO₄ was analyzed at 0.05 V s^− 1. The simultaneously collected voltammetric and nanogravimetric responses allowed to analyze the several electrochemical processes occurring in the studied range of potential, finishing with the formation of a thin film of ZnSe. The association of results obtained using both techniques was applied to identify the species involved in the AuO reduction as (AuO)₂H₂SeO₃, which was desorbed during the oxide reduction with a mass variation much larger than that one observed in the supporting electrolyte. Initially, the Se(IV) reduction results in Se_ads coverage, followed by a further reduction to H₂Se, which is a gas and desorbs from the electrode surface. Finally, the Zn(II) reduction inhibits the H₂Se formation and generates a thin film of ZnSe, as the final coating. The strong dependence of the nature of reacting compound and the mass as well as the charge variations allowed to postulate a reaction mechanism.     

Characterization and photocatalytic activity of nanostructured indium tin oxide thin-film electrode for azo-dye degradation

Photocatalytically active indium tin oxide thin film electrodes were prepared by electron beam evaporation technique onto a glass substrate having thickness 120 nm. Degradation of reactive dye yellow direct 42 has been performed using photoeletrocatalysis. A biased potential is applied across indium tin oxide photoelectrode illuminated by UV light. The best experimental conditions were found to be dye concentration 1.0 × 10^− 5 mol L^− 1, pH 5.25 and 0.5 mol L^− 1 NaCl as supporting electrolyte when the photoelectrode was biased at + 0.5 V versus saturated calomel electrode. The effects of other electrolytes, dye concentration, pH solution, electrode annealing temperature and applied potentials have been also investigated and are discussed. Several common inorganic salts Na₂SO₄, Na₂CO₃, NaNO₃ and NaCl were chosen to act as supporting electrolytes, which was added into the dye solution. It is shown that the charge-transfer resistance of photoanode can be calculated by the analysis of its electrochemical impedance spectroscopy, and the photoelectrocatalytic degradation rate of yellow direct 42 was inversely proportional to the value of charge-transfer resistance of photoelectrodes at different pH. The value of charge-transfer resistance is smaller, the higher its photoelectro-activity is.     

3D ordered NiO/silicon MCP array electrode materials for electrochemical supercapacitors

The preparation and electrochemical properties of 3D ordered nickel oxide/silicon microchannel plate (NiO/Si-MCP) array electrode materials for supercapacitors are studied. The Si-MCP fabricated by electrochemical etching is used as a 3D supporting structure for electrodes. The active NiO is synthesized by electroless plating of nickel on the surface of the Si-MCP followed by annealing under oxygen. The electrochemical properties of the NiO/Si-MCP nanocomposite electrode materials are studied using cyclic voltammetry (CV), chronopotentiometry, and electrochemical impedance spectroscopy (EIS) in a 2 M KOH solution. The results reveal typical electrochemical capacitive behavior in the potential range from −0.6 to 1.0 V. The specific capacitance of approximately 586.4 F g⁻¹ decreases slightly with 4.8% loss after 500 cycles. The linear and symmetrical charge/discharge curves are measured by chronopotentiometry. The NiO/Si-MCP composite is a promising electrode material for integrated supercapacitors.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Preparation and electrochemical performance of LiFePO4/C composite with carbon core structure

LiFePO₄/C composite with carbon core structure was successfully prepared by using araldite as carbon source. The microstructure and morphology of LiFePO₄/C composite were confirmed by X-ray diffraction and transmission electron microscopic observation. The experimental results show that this structure is entirely different from carbon coating. The LiFePO₄/C composite forms a common core structure in which carbon is used as line core and carbon core is covered by nano-LiFePO₄ grains. Moreover, the LiFePO₄/C composite exhibits higher tap density of 1.66 g cm^− 3, shows higher capacity about 162 mAhg^− 1 applied 30 mAg^− 1 current, excellent cyclic ability and rate capability about 139 mAhg^− 1 applied 700 mAg^− 1 current at room temperature.     

The effect of pure iron in a nanocrystalline grain size on the corrosion inhibitor behavior of sodium benzoate in near-neutral aqueous solution

The effect of grain size reduction on the electrochemical and corrosion behavior of iron with different grain sizes (32–750 nm) produced by direct and pulsed current electrodeposition were characterized using Tafel polarization curves and electrochemical impedance spectroscopy. The grain size of deposits was determined by X-ray diffraction analysis and scanning electron microscopy. The tests were carried out in an aqueous electrolyte containing 30 mg L⁻¹ NaCl + 70 mg L⁻¹ Na₂SO₄. Results obtained suggested that the inhibition effect and corrosion protection of sodium benzoate inhibitor in near-neutral aqueous solutions increased as the grain size decreased from microcrystalline to nanocrystalline. The improvement on the inhibition effect is attributed to the increase of the surface energy.     

Co2SnO4/activated carbon composite electrode for supercapacitor

A new kind of Co₂SnO₄-based electrode materials for supercapacitor was synthesized by co-precipitation method. The microstructure and surface morphology of Co₂SnO₄ were characterized by X-ray diffraction and scanning electron microscopy, respectively. Cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy were employed for the determination of specific capacitance and the equivalent series resistance of Co₂SnO₄/activated carbon composite electrode in KCl solution. It was shown that the composite electrode with 25 wt% Co₂SnO₄ had excellent specific capacitance up to 285.3 F g⁻¹ at the current density of 5 mA cm⁻². In addition, the composite electrode exhibited excellent long-term stability and, after 1000 cycles, 70.6% of initial capacitance was retained. Regarding the low cost, easy preparation, steady performance and environment friendliness, Co₂SnO₄/activated carbon composite electrode could have potentially promising application for supercapacitor.     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Nano-sized Li-Fe composite oxide prepared by a self-catalytic reverse atom transfer radical polymerization approach as an anode material for lithium-ion batteries

A novel Self-catalytic Reverse Atom Transfer Radical Polymerization (RATRP) approach that can provide the radical initiator and the catalyst by the system itself is used to synthesize a nano-sized Li-Fe composite oxide powder in large scale. Its crystalline structure and morphology have been characterized by X-ray diffraction and scanning electron microscopy. The results reveal that the composite is composed of nano-sized LiFeO₂ and Fe₃O₄. Its electrochemical properties are evaluated by charge/discharge measurements. The results show that the Li-Fe composite oxide is an excellent anode material for lithium-ion batteries with good cycling performance (1249 mAh g⁻¹ at 100th cycle) and outstanding rate capability (967 mAh g⁻¹ at 5 C). Such a self-catalytic RATRP approach provides a way to synthesize nano-sized iron oxide-based anode materials industrially with preferable electrochemical performance and can also be applied in other polymer-related area.     

Corrosion properties of a novel bulk Cu0.5NiAlCoCrFeSi glassy alloy in 288 °C high-purity water

Corrosion properties of a bulk Cu_0.5NiAlCoCrFeSi glassy alloy such as electrochemical corrosion potential (ECP), potentiodynamic polarization, and weight loss measurements were carried out for the first time in 288 °C high-purity (outlet conductivity < 0.07 μS cm^− 1) water. The change of ECP with dissolved oxygen (DO) showed a sigmoid curve. In addition, the Cu_0.5NiAlCoCrFeSi alloy exhibited a wide passive region and the passive current density was ∼ 2 × 10^− 4 A cm^− 2 in deaerated water containing 0.01 N sodium sulfate (Na₂SO₄) at 288 °C. A very low weight loss of ∼ 4.5 μg mm^− 1 was also found for the Cu_0.5NiAlCoCrFeSi alloy after immersion in deaerated 288 °C water for 12 weeks.     

High capacitive performance of nanostructured Mn-Ni-Co oxide composites for supercapacitor

Nanostructured Mn-Ni-Co oxide composites (MNCO) were prepared by thermal decomposition of the precursor obtained by chemical co-precipitation of Mn, Ni and Co salts. The chemical composition and morphology were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The electrochemical capacitance of MNCO electrode was examined by cyclic voltammetry, impedance and galvanostatic charge-discharge measurements. The results showed that MNCO electrode exhibited the good electrochemical characteristics. A maximum capacitance value of 1260 F g⁻¹ could be obtained within the potential range of −0.1 to 0.4 V versus saturated calomel electrode (SCE) in 6 mol L⁻¹ KOH electrolyte.     

Low-temperature synthesis of δ-MnO2 with large surface area and its capacitance

δ-MnO₂ was synthesized by a facile low-temperature hydrothermal method with a mixed system of KMnO₄ and CO(NH₂)₂ at 90 °C for 24 h. The obtained product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N₂ adsorption-desorption. Results showed that the as-synthesized product had a layered structure and a high specific surface area of 230 m² g^− 1. Electrochemical characterization indicated that the prepared material exhibited an ideal capacitive behavior with the initial capacitance value of 265 F g^− 1 in 1 mol L^− 1 Na₂SO₄ aqueous solution at a scan rate of 5 mV s^− 1 and excellent cycling behavior.     

Development of redox deposition of birnessite-type MnO2 on activated carbon as high-performance electrode for hybrid supercapacitors

Birnessite-type MnO₂/activated carbon nanocomposites have been synthesized by directly reducing KMnO₄ with activated carbon in an aqueous solution. It is found that the morphologies of MnO₂ grown on activated carbon can be tailored by varying the reaction ratio of activated carbon and KMnO₄. An asymmetric supercapacitor with high energy density was fabricated by using MnO₂/activated carbon (MnO₂/AC) nanocomposite as positive electrode and activated carbon as negative electrode in 1 M Na₂SO₄ aqueous electrolyte. The asymmetric supercapacitor can be cycled reversibly in the cell voltage of 0–2 V, and delivers a specific capacitance of 50.6 F g⁻¹ and a maximum energy density of 28.1 Wh kg⁻¹ (based on the total mass of active electrode materials of 9.4 mg), which is much higher than that of MnO₂/AC symmetric supercapacitor (9.7 Wh kg⁻¹).     

Rapid synthesis of homogeneous MnO2/multi-wall carbon nanotubes nanostructure and its electrochemical capacitive behavior

A homogeneous composite of MnO₂/multi-wall carbon nanotubes (MnO₂/MWCNTs) was rapidly and efficiently synthesized by a redox reaction of MnO₄⁻ and Mn²⁺ on the MWCNTs under ultrasonic irradiation. The structure and morphology of the obtained MnO₂ and MnO₂/MWCNTs composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. Electrochemical investigation indicated that the maximum specific capacitance of the MnO₂/MWCNTs composite, measured by galvanostatic charge-discharge test, was 315 F g^− 1, compared to the pristine MnO₂ (192 F g^− 1) and MWCNTs electrode (25 F g^− 1), showing the synergistic effect of MWCNTs and MnO₂. The homogeneous hybrid nanostructure and the good conductivity of MWCNTs were considered to be responsible for its preferable electrochemical performances.     

Electrochemical preparation of NiAl intermetallic compound from solid oxides in molten CaCl2 and its corrosion behaviors in NaCl aqueous solution

Nickel aluminide powders were prepared by direct electrochemical reduction of solid mixture of NiO–NiAl₂O₄ (Ni:Al = 1:1 in mol) precursor in molten CaCl₂ at 850 °C. The reduction process of the solid oxide cathode was investigated by analyzing the intermediate products using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It reveals that nickel is preferentially reduced and it benefits to prevent aluminum leaving from the cathode. The products obtained at the constant cell voltage electrolysis of 3.0 V for more than 4 h were stoichiometric NiAl. The energy consumption could be as low as 6.1 kWh (kg-NiAl)⁻¹ based on the applied cell voltage and the consumed electrolysis charge. Furthermore, the NiAl powders were made into a dense rod by spark plasma sintering (SPS) technique. The corrosion behaviors of the NiAl rod in 0.5 mol L⁻¹ NaCl aqueous solution at room temperature were investigated by polarization curve and ac impedance measurements. It was found that the NiAl rod had satisfactory anti-corrosion ability in the solution.     

Fabrication horizontal aligned MoO2/single-walled carbon nanotube nanowires for electrochemical supercapacitor

The horizontally aligned MoO₂/single-walled carbon nanotube (MoO₂/SWNT) composite has been prepared by electrochemically induced deposition method which utilizes the good electronic conductivity of SWNTs as supporting material to deposit MoO₂. The morphology and crystal structure of the composite were investigated by X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. The capacitive properties of the MoO₂/SWNT composites have been investigated by cyclic voltammetry (CV). A specific capacitance (based on MoO₂) as high as 597 F g^− 1 is obtained at a scan rate of 10 mV s^− 1 in 0.1 M Na₂SO₄ aqueous solution. Additionally, the MoO₂/SWNT composites electrode shows excellent long-term cycle stability (only 2.5% decrease of the specific capacitance is observed after 600 CV cycles).     

Preparation and electrochemical performance of manganese oxide/carbon nanotubes composite as a cathode for rechargeable lithium battery with high power density

Manganese oxide/carbon nanotubes (MO/CNTs) composite was prepared by hydrothermally reducing KMnO₄ with CNTs, where the used CNTs are of dual role, i.e., they serve as reductant during reaction and the remaining CNTs act as conducting agent in the composite. This composite was characterized by X-ray diffraction and scanning electron microscopy techniques. In addition, the electrochemical performances of the composite were investigated, which suggested an excellent rate-capability of this material; e.g., it delivered a high discharge capacity as 131 mAh g^− 1 at a high current density of 4 A g^− 1 (20 C), and high capacity at low discharge current density, e.g., about 209 mAh g^− 1 at 0.2 C rate. Therefore, such a MO/CNTs composite is promising in high power application of lithium battery and electrochemical capacitor.