Electrochemical behaviour of LaCl3 at tungsten and aluminium cathodes in LiCl–KCl eutectic melt

The electrochemical behaviour of lanthanum was studied at inert tungsten electrode and reactive aluminium electrode in LiCl–KCl eutectic melt in the temperature range 698–798 K using transient electrochemical techniques. Reduction of La(III) to La(0) at the tungsten electrode takes place in a single step. The reduction shows quasi-reversible behaviour for polarization rates, 25 ≤ ν ≤ 150 mV s^?1 and is predominantly controlled by charge transfer of La(III) ions for scan rates higher than 75 mV s^?1. The heterogenous rate constant of the process was estimated from impedance spectroscopy and from the semi-integrals of the cyclic voltammograms. The redox potential of the La(III)/La couple at the Al electrode was observed to be more positive than that at the inert electrode. This potential shift is due to the lowering of the activity of La in the metal phase caused by the formation of the intermetallic compound Al₁₁La₃. Thermodynamic properties such as Gibbs energy of formation of Al₁₁La₃, excess Gibbs energy and the activity coefficient of La in Al were calculated from the open circuit potential measurement.     

Study of electrochemical performances of perovskite-type oxide LaGaO3 for application as a novel anode material for Ni-MH secondary batteries

In this paper, the perovskite-type oxide LaGaO₃, which is proposed as a novel anode material for Ni-MH secondary batteries, was synthesized by the sol–gel method. The electrochemical performance of the oxide was analyzed at temperature 328 K using chronopotentiometry, potentiodynamic polarization and chronoamperomertry techniques. During the first three of charge/discharge cycles, the discharge capacity of the oxide LaGaO₃ reaches its maximum value at 220 mAh g⁻¹ and thereafter decreases. The degradation of cycling stability of the oxide can be explained by the corrosion behavior of the electrode as a result of the decrease in the electroactive surface area of the electrochemical reaction with cycling. The kinetic results showed that both the exchange current density I₀ and the hydrogen diffusion coefficient D_H of the anode decrease with increasing state of charge, after activation, which can be ascribed to the change in the electrode surface when transforming from α to β phase. The whole electrochemical reactions of the electrode are governed by two important processes: charge-transfer reaction on the electrode surface and hydrogen atom diffusion within the bulk of the electrode.     

Synthesis,characterization and electrochemical performance of Sn3F3PO4 anode material for lithium-ion batteries

Tin fluorophosphate (Sn₃F₃PO₄) powder was synthesized via a microemulsion route. Physical properties of the synthesized material were investigated by means of X-ray powder diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The investigation showed that the synthesized powder was crystalline Sn₃F₃PO₄ with needle-like morphology with a thickness of 300–500 nm and length of 5–10 μm. The electrochemical performance of the synthesized powder as a negative electrode for Li-ion batteries was studied. The results showed that the synthesized Sm₃F₃PO₄ possessed an initial discharge capacity of 1370 mAh g^?1 and charge capacity of 968 mAh g^?1 in a potential range of 0.005–3 V. In addition, the material showed capacity retention of 70.8% after 30 cycles at a constant current density of 100 mA g^?1.     

Effect of molybdenum substitution on electrochemical performance of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode material

Molybdenum doping is introduced to improve the electrochemical performance of lithium-rich manganese-based cathode material. X-ray diffraction (XRD) results illustrate that the crystallographic parameters a, c and lattice volume V become larger with the increase of Mo content. The scanning electron microscope (SEM) shows that the molybdenum substitution increases the crystallinity of the primary particles. When evaluated as cathode material, the as-prepared Li[Li_0.2Mn_0.54-x/3Ni_0.13-x/3Co_0.13-x/3Mo_x]O₂ (x = 0.007) delivers a discharge capacity of 155.5 mA h g⁻¹ at 5 C (1 C = 250 mA g⁻¹) and exhibits the capacity retention of 81.8% at 1 C after 200 cycles. The results of cyclic voltammetry (CV) and electronic impedance spectroscopy (EIS) tests reflect that the molybdenum substitution is able to significantly reduce the electrode polarization and lower the charge-transfer resistance. Within appropriate amount of Mo doping, the lithium ion diffusion coefficient of the material can reach to 8.92 × 10^–15 cm² s⁻¹, which is ~ 30 times higher than that of pristine materials (2.65 × 10^–16 cm² s⁻¹).     

A nickel hexacyanoferrate and poly(1-naphthol) hybrid film modified electrode used in the selective electroanalysis of dopamine

A mixed-valent nickel hexacyanoferrate and poly(1-naphthol) hybrid (NiHCF–PNH) film was prepared on a gold (Au) electrode by a galvanostatic method, which led to stable and homogeneous hybrid film. The film was characterized using scanning electronic microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. This electrode showed excellent catalytic properties toward dopamine (DA) detection, using cyclic voltammetry and differential pulse voltammetry methods. The electrocatalytic oxidations of DA at different electrodes, such as a bare Au electrode or a poly(1-naphthol)/Au-, or NiHCF–PNH/Au-modified electrode, were investigated in a phosphate buffer solution (pH 7). Interestingly, the NiHCF–PNH-modified electrode facilitated the oxidation of DA, but it did not responded to other electroactive biomolecules, such as ascorbic acid and uric acid_. The DA electrochemical sensor exhibited a linear response from 0.1 to 4.3 μM (R² = 0.9984) and from 4.3 to 9.6 μM (R² = 0.9969), with a detection limit of 2.1 × 10^?8 M, and a short response time (3 s) for DA determination. In addition, the NiHCF–PNH-modified electrode exhibited distinct advantages by its simple preparation, specificity, and stability.     

Analysis of electrochemical mechanism of coprecipitated nano-Ag4Bi2O5 as super high charge–discharge rate cathode materials for aqueous rechargeable battery

Nano Ag₄Bi₂O₅ as a novel cathode material of rechargeable alkaline batteries was successfully synthesized by precise control of precipitation reaction. KOH solution was used as precipitant and a mixture of AgNO₃ and Bi(NO₃)₃ as Ag–Bi source. The experimental results indicate that concentration of KOH, reaction temperature and PH value have the effects on the structure and electrochemical property of the product. The material was characterized by means of XRD, FSEM and TG–DSC. The results show that the sample is single crystals with 50–100 nm in width and 600–800 nm in length. The electrochemical performances of Ag₄Bi₂O₅ in the alkaline electrolyte were measured by galvanostatic method and cyclic voltammetry tests through film electrode. The sample shows three typical procedures during the charge–discharge, corresponding to Ag(II)–Ag(I), Ag(I)–Ag(0) and Bi(III)–Bi(0) transformation processes. This result is also verified by XRD tests. The Ag₄Bi₂O₅ electrode has excellent electrochemical properties. It undergoes a current density as high as 20 A g^?1, which greatly reduces charge time down to 55.9 s. The electrode offers a cycling capacity of 330 mAh g^?1 and a cycling life more than 400 cycles at 1–2 A g^?1.     

Properties of NiFe2O4 ceramics from powders obtained by auto-combustion synthesis with different fuels

Nickel ferrite (NiFe₂O₄) powders derived by auto-combustion synthesis using three different fuels (citric acid, glycine and dl-alanine) have been characterized. The sintering behavior of ceramics using these powders has been compared. Oxygen balance (OB) setting for the chemical reaction is found to regulate the combustion reaction rate. A rapid reaction rate and a high flame temperature are achieved with dl alanine fuel yielding single phase NiFe₂O₄ powder in the as-burnt stage, whereas powders derived with citric acid and glycine fuels show poor crystallinity and necessitate post-annealing. The powder particles are largely agglomerated with a non-uniform distribution in shape and size, and the average particle size is estimated in the range ~ 54–71 nm. Powders derived from dl-alanine fuel show better phase purity, smaller crystallite size, larger surface area and superior sintering behavior. Additional Raman modes discerned for dl-alanine derived powder support a 1:1 ordering of Ni²⁺ and Fe³⁺ at the octahedral sites relating to microscopic tetragonal P4₁22 symmetry expected theoretically for the formation of NiFe₂O₄ with inverse spinel structure. Microstructure of sintered ceramics depends on the precursor powders that are used and sintering at 1200 °C is found to be optimum. Citric acid and glycine derived powders yield high saturation magnetization (M_s~47–49 emu/g), but poor dielectric properties, whereas dl-alanine derived powders yield ceramics with high resistivity (~3.4×10⁸ Ω cm), low dielectric loss (tan δ~0.003 at 1 MHz) and high magnetization (46 emu/g). Dielectric dispersion and impedance analysis show good correlation with the changes in the ceramic microstructure.     

Magnetic,magnetostrictive, and AC impedance properties of manganese substituted cobalt ferrites

In this study, we investigated the effects of substituting Mn³⁺ for some Fe³⁺ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMn_xFe_2−xO₄, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λ_S), about −167 ppm, and the CoMn_0.2Fe_1.8O₄ sample exhibited the highest strain sensitivity (|dλ_⊥/dH|_m) of 2.23×10⁻⁹ A⁻¹m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.     

The composite material based on Dawson-type polyoxometalate and activated carbon as the supercapacitor electrode

A supercapacitor electrode assembled from activated carbon (AC) and (NH₄)₆[P₂Mo₁₈O₆₂]·14.2H₂O (P₂Mo₁₈) was fabricated for the first time, and showed remarkable electrochemical performance ascribed to the synergy of the double layer capacitance of AC and the pseudocapacitance of P₂Mo₁₈. The investigations indicate that the AC/P₂Mo₁₈ electrode exhibits a specific capacitance of 275 F g^− 1 at a high current density of 6 A g^− 1, which is substantially larger than the 182 F g^− 1 of the AC electrode. In addition, the AC/P₂Mo₁₈ electrode possesses a remarkable rate capability (89%) when the current density is increased from 2 to 6 A g^− 1.     

Sol–emulsion–gel synthesis of cordierite ceramics for high-frequency multilayer chip inductors

Nano-Cordierite powders used for high frequency chip inductors (MLCIs) were prepared by sol–emulsion–gel method. Effects of precursor concentration and [H₂O]/[Si] molar ratio on this material were studied. The sol–emulsion–gel processing of Mg₂Al₄Si₅O₁₈ as well as its dielectric property were investigated. Owing to the better packing efficiency and therefore higher surface energy of the freestanding nano-powder, the pressed pellets made by cordierite powder showed 98.6% theoretical density at 900 °C for 2 h. The additive Bi₂O₃ was utilized to promote the crystallization or transformation to α-cordierite and sintering. The sol–emulsion–gel-derived cordierite ceramics have low dielectric constant (ε=3.0～4.0; 18 GHz) and low dielectric loss (tgδ<0.001; 18 GHz) and can be co-fired with high conductivity metals such as Au, Ag/Pd internal electrode at low temperature (900 °C), suggesting that it was an ideal dielectric material for high-frequency multilayer chip inductors.     

High-performance supercapacitor based on V2O5/carbon nanotubes-super activated carbon ternary composite

A ternary composite of V₂O₅/carbon nanotubes/super activated carbon (V₂O₅/CNTs–SAC) was prepared by a simple hydrothermal method and used as a supercapacitor electrode material. The electrochemical performance of the electrode was analyzed using cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy, which were performed in 2 M NaNO₃ as the electrolyte. The V₂O₅/CNTs–SAC nanocomposite exhibited a specific capacitance as high as 357.5 F g⁻¹ at a current density of 10 A g⁻¹, which is much higher than that of either bare V₂O₅ nanosheets or a V₂O₅/CNTs composite. Furthermore, the capacitance increased to 128.7% of the initial value after 200 cycles, with 99.5% of the maximum value being retained after 1000 cycles. These results demonstrated that the V₂O₅/CNTs–SAC ternary composite is suitable for use as an electrode material for supercapacitors.     

Extrusion of AlSBA-15 molecular sieves: An industrial point of view

AlSBA-15 in the powder form with different n_Si/n_Al ratios (45, 136 and 215) were synthesized by hydrothermal technique. The powdered materials were made into cylindrical extrudates with the addition of bentonite as a binder. The AlSBA-15 materials were characterized by XRD, N₂ adsorption, AAS and thermogravimetric analysis. The orderly growth of AlSBA-15 is evidenced by its XRD. The surface area of the powder catalyst is around 950 m²/g and that of extrudate is close to 600 m²/g. Vapor phase alkylation of phenol with tert-butanol was carried out over the extrudates of AlSBA-15 as a model reaction. The activity of AlSBA-15 extrudates follows the order: AlSBA-15 Si/Al = 45 > AlSBA-15 Si/Al = 136 > AlSBA-15 Si/Al = 215. The reaction products were found to be 2-TBP, 4-TBP and 2,4-DTBP. The selectivity to para tertiary butylation is higher than other reactions.     

Sol-gel synthesis of new TiO2/activated carbon photocatalyst and its application for degradation of tetracycline

A new efficient photocatalyst consisting of TiO₂-activated carbon composite (TiO₂/AC) was synthesized by sol-gel process and applied to decomposition of tetracycline (TC). Its properties and catalytic activity were evaluated in comparison with bare TiO₂ and P25, based on several characterization techniques and TC photodegradation kinetic studies. The results showed TiO₂/AC has better structural and electronic features for photocatalysis; S_BET of 129 m² g^–1, exclusively anatase phase, crystal size of 8.53 nm and band gap energy of 3.04 eV. The catalytic activity of the material was evaluated based on photodegradation kinetic studies of TC from aqueous solution (with initial concentration=50 mg L⁻¹ and catalyst dosage=1.0 g L⁻¹). Non-linear kinetic model of pseudo-first order were fitted to the resulting experimental data. The apparent first-order rate constant (k_app=42.9×10^–3 min^–1) and half-life time (t_1/2=16.1 min) determined for TiO₂/AC were better than those for P25 and bare TiO₂. TC degradation by-products were investigated by HPLC-MS, showing TC was completely degraded after 75 min, producing fragments with m/z smaller than 150.     

Improved activity of a graphene–TiO2 hybrid electrode in an electrochemical supercapacitor

We present a simple and fast approach for the synthesis of a graphene–TiO₂ hybrid nanostructure using a microwave-assisted technique. The microstructure, composition, and morphology were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Structural analysis revealed a homogeneous distribution of nanosized TiO₂ particles on graphene nanosheets. The material exhibited a high specific capacitance of 165 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte solution. Theenhanced supercapacitance property of these materials could be ascribed to the increased conductivity of TiO₂ and better utilization of graphene. Moreover, the material exhibited long-term cycle stability, retaining ∼90% specific capacitance after 5000 cycles, which suggests that it has potential as an electrode material for high-performance electrochemical supercapacitors.     

Preparation of ultra-fine Sm0.2Ce0.8O1.9 powder by a novel solid state reaction and fabrication of dense Sm0.2Ce0.8O1.9 electrolyte film

A novel solid state reaction was adopted to prepare Sm_0.2Ce_0.8O_1.9 (SDC) powder. A mixed oxalate Sm_0.2Ce_0.8(C₂O₄)_1.5·2H₂O was synthesized by milling a mixture of cerium acetate hydrate, samarium acetate hydrate, and oxalic acid for 5 h at room temperature. An ultra-fine SDC powder with the primary particle size of 5.5 nm was obtained at 300 °C. The ultra-low temperature for the formation of SDC phase was due to the atomic level mixture of the Sm³⁺ and Ce⁴⁺ ions. The crystal sizes of SDC powders at 300 °C, 550 °C, 800 °C, and 1050 °C were 5.5 nm, 11.4 nm, 24.1 nm and 37.5 nm, respectively. The sintering curves showed that the powder calcined at lower temperature was easier to be sintered owning to its smaller particle size. A solid oxide electrolytic cell (SOEC), comprising porous La_0.8Sr_0.2Cu_0.1Fe_0.9O_3−δ (LSCF) for substrate, LSCF–SDC for active electrode, SDC for electrolyte, and LSCF–SDC for symmetric electrode, was fabricated by dip-coating and co-sintering techniques. An extremely dense SDC film with the thickness of 20 μm was obtained at only 1200 °C, which was about 100–300 °C lower than the literatures׳ reports. The designed SOEC was proved to work effectively for decomposing NO (3500 ppm, balanced in N₂), 80% NO can be decomposed at 600 °C.     

Synthesis,structural and electrical properties of novel pyrochlores in the Bi2O3–CuO–Ta2O5 ternary system

A series of non-stoichiometric cubic pyrochlores with general formula, Bi_3?xCu_1.8Ta_3+xO_13.8+x (BCT) was successfully prepared by solid state reaction at the firing temperature of 950 °C over 2 days. The solid solution mechanism is proposed as one-to-one replacement of Bi³⁺ for Ta⁵⁺, together with a variation in oxygen content in order to achieve electroneutrality. The solid solution limit is confirmed by X-ray diffraction technique (XRD) for which linear variation of lattice constants is observed at 0 ≤ x ≤ 0.6. The refined lattice constants are found to be in the range of 10.4838 (8) Å–10.5184 (4) Å and the grain sizes of these samples determined by scanning electron microscopy (SEM) fall between 1 and 40 μm. Meanwhile, thermal analyses show no physical or chemical change for the prepared pyrochlores. The relative densities of the densified pellets for AC impedance measurements are above 85% and the measured relative permittivity, ?′ and dielectric loss, tan δ for composition, x = 0.2 at ambient temperature are ～60 and 0.07 at 1 MHz, respectively. The calculated activation energies are 0.32–0.40 eV and the conductivity values, Y′ are in the order of 10^?3 at 400 °C. The conduction mechanisms of BCT pyrochlores are probably attributed to the oxygen non-stoichiometry and mixed valency of copper within the structure.     

Facile synthesis of Sm2S3 diffused nanoflakes and their pseudocapactive behavior

The Sm₂S₃ thin films with diffused nanoflakes morphology are prepared by an environment-friendly facile chemical synthesis method and used in electrochemical supercapacitors. The structural, elemental and surface morphological characterization are carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and wettability techniques. The FESEM images show tree root like distribution of flakes with average flake width of about 80 nm. The film surface is lyophilic with propylene carbonate contact angle of 21°. The supercapacitive measurements are carried out through cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm₂S₃ film electrode exhibited a highest specific capacitance (C_s) of 213 Fg⁻¹ at 5 mVs⁻¹ scan rate in LiClO₄-propylene carbonate electrolyte. Asymmetric nature of charge–discharge curves confirmed pseudocapacitive behavior of electrode with energy and power densities of 39.39 Whkg⁻¹ and 4.33 kWkg⁻¹, respectively. An equivalent series resistance of 0.44 Ωcm⁻² indicated negligible ohmic losses in charge storage. An electrochemical stability of 81.47% is retained after 1000 cycles indicating that Sm₂S₃ is a promising candidate for supercapacitor application.     

Enhanced electrochemical properties of LiFePO4–silicon composites as positive electrode materials fabricated using a solid-state method

LiFePO₄–silicon composites were fabricated by using a solid-state method for applying positive electrodes in lithium ion batteries. The LiFePO₄–silicon composites were characterized with X-ray diffraction and field emission scanning electron microscopy. Their electrochemical properties were investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The added silicon not only suppressed the surface corrosion caused by the decreasing H⁺ concentration in the electrolyte, but it also acted as a barrier between the LiFePO₄ particles and LiPF₆ electrolyte, thereby preventing the dissolution of Fe²⁺ in the electrode and enhancing the electrolyte/active material interactions. This resulted in improved lithium-ion transfer kinetics and excellent positive electrode performance, especially at high current densities and different operating temperatures (0, 25, and 50 °C). At 25 °C, the LiFePO₄ composite containing 2 wt% of silicon delivered the best electrochemical performance with a lithium-ion diffusion coefficient of 1.81×10⁻⁹ cm² s⁻¹, a specific discharge capacity of 143 mA h g⁻¹ for the initial cycle, and a capacity retention of 98% after 100 cycles. In contrast, the corresponding values for the pure LiFePO₄ were 1.19×10⁻¹¹ cm² s⁻¹, 115 mA h g⁻¹, and a capacity retention of 76% after 100 cycles, respectively.     

Heat generation properties in AC magnetic field for Y3Fe5O12 powder material synthesized by a reverse coprecipitation method

Ferrimagnetic Y₃Fe₅O₁₂ powder was synthesized by a reverse coprecipitation method in order to study its heat generation property in an AC magnetic field. An orthorhombic YFeO₃ phase having a small particle size (<100 nm) was obtained for the samples calcined at a low temperature. The maximum heat generation ability in an AC magnetic field was obtained for the Y₃Fe₅O₁₂ ferrite powder by calcination at 1100 °C. The heat generation ability was reduced for the samples calcined at a higher temperature. The particle growth with the formation of the cubic single phase might influence the heat generation ability. The heat generation ability and the hysteresis loss value were proportional to the cube of the magnetic field (H³), because the coercivity value of the B–H curve was proportional to the square of the amplitude of the AC magnetic field (H²). The heat generation ability (W g⁻¹) of the Y₃Fe₅O₁₂ sample sintered at 1100 °C can be expressed by the equation 2.2×10⁻⁴∙f∙H³ using the frequency (f/kHz) and the magnetic field (H/kA m⁻¹), which has the highest heat generation ability of the reported magnetic materials. The hysteresis loss value for the B–H curve agreed with the heat generation ability of the samples calcined at 1100 °C and lower temperatures.     

Co9S8–carbon composite as anode materials with improved Na-storage performance

The synthesis and electrochemical performance of a composite of Co₉S₈ nanoparticles and amorphous carbon is studied as an anode material for sodium-ion batteries. The Co₉S₈–carbon composite powder was fabricated through a one-pot spray pyrolysis process using thiourea and polyvinylpyrrolidone as sulfur and carbon sources, respectively. The Co₉S₈ nanoparticles are entirely covered by an amorphous carbon layer. The initial discharge and charge capacities of the Co₉S₈–carbon composite powder were 689 and 475 mA h g⁻¹, respectively, at a current density of 0.5 A g⁻¹. The Co₉S₈–carbon composite powders exhibited a stable cyclability with a reversible capacity of 404 mA h g⁻¹ for the 50th cycle and a superior rate capability compared with bare Co_1−xS powder. The improvement of Na-storage performance could be attributed to the small size and entanglement of the Co₉S₈ nanoparticles within the carbon matrix.