Polyvinylpyrrolidone-assisted synthesis of microscale C-LiFePO4 with high tap density as positive electrode materials for lithium batteries

Carbon-coated LiFePO₄ (C-LiFePO₄) with micron particle size (6 μm) and high tap density (1.6 g cm⁻³) was prepared from spherical FePO₄·2H₂O powder via the co-precipitation method. The C-LiFePO₄ powder was calcined at temperatures between 650 and 800 °C. The 6 μm C-LiFePO₄ prepared at 800 °C exhibited an excellent rate capability, delivering 150 mAh g⁻¹ on discharge at the 0.1 C-rate and 108 mAh g⁻¹ at the 5 C-rate. The volumetric capacity of the 6 μm C-LiFePO₄ corresponded to 225 mAh cm⁻³, since the large secondary particles (6 μm) C-LiFePO₄ sufficiently allowed tight packing of the particles. The 6 μm C-LiFePO₄ powder with high tap density makes an attractive positive electrode candidate for lithium-ion batteries designed for high energy density.     

Preparation of titanium nitride ultrafine powders by sol–gel and microwave carbothermal reduction nitridation methods

Titanium nitride ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave carbothermal reduction methods. The influences of reaction temperature, molar ratio of Ti to C, addition of crystal seeds and amount of NH₄F on the synthesis of titanium nitride were studied. The results show that excess amount of carbon, addition of crystal seeds and NH₄F plays a positive effect on the preparation of TiN at low temperature. The inceptive formation temperature of TiN ultrafine powders is about 800 °C, and pure TiN can be prepared at 1000 °C. Field emission-scanning electron microscopy (FE-SEM) was used to get the micrograph of the TiN powder, it shows that the size of the powders synthesized at 1000 °C is about 0.1–0.5 μm.     

Electrochemical reaction of the SiMn/C composite for anode in lithium ion batteries

The SiMn-graphite composite powder was prepared by mechanical ball milling and its electrochemical performances were evaluated as the candidate anode materials for lithium ion batteries. It is found that the cyclic performance of the composite materials is improved significantly compared to SiMn alloy and pure silicon. The heat treatment of the electrodes is beneficial for enhancing the cyclic stabilities. The SiMn-20 wt.% graphite composite electrode after annealing at 200 °C has an initial reversible capacity of 463 mAh g⁻¹ and a charge-discharge efficiency of 70%. Moreover, the reversible capacity maintains 426 mAh g⁻¹ after 30 cycles with a coulomb efficiency of over 97%. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electron microscopy. The lithiation/delithiation behavior was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composite materials appear to be promising candidates as negative electrodes for lithium rechargeable batteries.     

Development of a new graded-porosity FeAl alloy by elemental reactive synthesis

A new graded-porosity FeAl alloy can be fabricated through Fe and Al elemental reactive synthesis. FeAl alloy with large connecting open pores and permeability were used as porous supports. The coating was obtained by spraying slurries consisting of mixtures of Fe powder and Al powder with 3-5 μm diameter onto porous FeAl support and then sintered at 1100 °C. The performances of the coating were compared in terms of thickness, pore diameter and permeability. With an increase in the coating thickness up to 200 μm, the changes of maximum pore size decreased from 23.6 μm to 5.9 μm and the permeability decreased from 184.2 m³ m^− 2 kPa^− 1 h^− 1 to 76.2 m³ m^− 2 kPa^− 1 h^− 1, respectively, for a sintering temperature equal to 1100 °C. The composite membranes have potential application for excellent filters in severe environments.     

A novel micro-spherical CoSn2/Sn alloy composite as high capacity anode materials for Li-ion rechargeable batteries

Micro-scaled spherical CoSn₂/Sn alloy powders synthesized from oxides of Sn and Co via carbothermal reduction at 800 °C were examined for use as anode materials in Li-ion battery. The phase composition and particle morphology of the CoSn₂/Sn alloy composite powders were investigated by XRD, SEM and TEM. The prepared CoSn₂/Sn alloy composite electrode exhibits a low initial irreversible capacity of ca. 140 mAh g⁻¹, a high specific capacity of ca. 600 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and a good rate capability. The stable discharge capacities of 500-515 mAh g⁻¹ and the columbic efficiencies of 95.8-98.1% were obtained at current density of 500 mA g⁻¹. The relatively large particle size of CoSn₂/Sn alloy composite powder is apparently favorable for the lowering of initial capacity loss of electrode, while the loose particle structural characteristic and the Co addition in Sn matrix should be responsible for the improvement of cycling stability of CoSn₂/Sn electrode.     

Preparation of a new ceramic microfiltration membrane from mineral coal fly ash: Application to the treatment of the textile dying effluents

New microfiltration membranes from mineral coal fly-ash material are obtained using ceramic method. Paste from mineral coal fly ash (obtained by calcinations at 800 °C of non-grinded mineral coal) is extruded to elaborate a porous tubular configuration used as supports. The support heated at 1125 °C, shows an average pore diameter and porosity of about 4.5 μm and 51%, respectively. The properties in terms of mechanical and corrosion resistances are very interesting. The elaboration of the layer based on fly-ash powder (obtained by sintering at 700 °C of a finely grinded mineral coal) is performed by slip-casting method. The heating treatment at 800 °C leads to an average pore size of 0.25 μm. The water permeability determined of this membrane is 475 L/h m² bar. This membrane can be used for crossflow microfiltration. The application to the treatment of the dying effluents generated by the washing baths in the textile industry shows an important decrease of turbidity (inferior to 1 NTU), of chemical oxygen demand (COD) values (retention rate of about 75%) and a total color removal. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 L h⁻¹ m⁻²). So, it seems that the prepared membrane is suitable for such wastewater treatment.     

Ceramic electrodes for an alkali metal thermo-electric converter (AMTEC)

TiN, TiC, TiC/TiN, and Mo electrodes for an Alkali Metal Thermo-Electric Converter (AMTEC) were prepared by ceramic processing and their cathodic polarization characteristics were studied at 600–800°C. The polarization characteristics for TiN and TIC electrodes were similar to those for the Mo electrode. Among three kinds of TiC electrodes with different morphologies, the electrode consisting of finer grains gave a higher power density (0.40 W cm^–2). The activation energies for the exchange current density were smaller for ceramic electrodes than for the Mo electrode. In the high current density region above about 1 A cm^–2, a limiting current region appeared. When the vacuum level of the low temperature region, which was controlled by introduction of argon, was below 10 Pa, the power density did not depend on the vacuum level but, above 10 Pa, the power density decreased with increase of argon pressure.     

Electrochemical properties of Sr1−xCexMnO3 (0.1≤x≤0.4) – GDC composite cathodes for IT-SOFCs

The electrochemical properties of Sr_1−xCe_xMnO₃ (SCM, 0.1≤x≤0.4)–Gd_0.2Ce_0.8O_2−x (GDC) composite cathodes were determined by impedance spectroscopy. The study focused on the doping effect of Ce in the composite cathodes. Single-phase perovskite was obtained for 0.1≤x≤0.3 in SCM. No reaction occurred between the Sr_0.7Ce_0.3MnO₃ electrode and the GDC electrolyte at an operating temperature of 800 °C for 100 h. In the single phase perovskite region, lattice expansion occurred due to the reduction of Mn⁴⁺ to Mn³⁺ at B-sites, and this was attributed to an increase in Ce content. Ce doping enhanced the electrode performance of SCM–GDC composite cathodes, and best electrode performance was achieved for the Sr_0.7Ce_0.3MnO₃–GDC composite cathode (0.93 Ω cm² and 0.47 Ω cm² at 750 °C and 800 °C, respectively). The improvement in electrode performance was attributed to increases in charge carriers induced by a shift of some Mn from +4 to +3 and to the formation of surface oxygen vacancies caused by Mn⁴⁺ to Mn³⁺ conversion at high temperatures.     

Micromolar determination of sulfur oxoanions and sulfide at a renewable sol-gel carbon ceramic electrode modified with nickel powder

The sol-gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The nickel powder successfully used to deposit NiO_x thin film on conductive carbon ceramic electrode for large surface area catalytic application. Repetitive cycling in potential range −0.2 to 1.0 V was used to form of a thin nickel oxide film on the surface carbon composite electrode. The thin film exhibits an excellent electro-catalytic activity for oxidation of SO₃²⁻, S₂O₄²⁻, S₂O₃²⁻, S₄O₆²⁻ and S²⁻ in alkaline pH range 10-14. Optimum pH values for detection of all sulfur derivatives is 13 and catalytic rate constants are in range 2.4 × 10³-8.9 × 10³ M⁻¹ s⁻¹. The hydrodynamic amperometry at rotating modified CCE at constant potential versus reference electrode was used for detection of sulfur derivatives. Under optimized conditions the calibration plots are linear in the concentration range 10 μM-15 mM and detection limit 1.2-34 μM and 0.53-7.58 nA/μM (sensitivity) for electrode surface area 0.0314 cm². The nickel powder doped modified carbon ceramic electrode shows good reproducibility, a short response time (2.0 s), remarkable long term stability, less expense, simplicity of preparation, good chemical and mechanical stability, and especially good surface renewability by simple mechanical polishing and repetitive potential cycling. This sensor can be used into the design of a simple and cheap chromatographic amperometry detector for analysis of sulfur derivatives.     

Facile solvothermal synthesis of a graphene nanosheet-bismuth oxide composite and its electrochemical characteristics

This work demonstrates a novel and facile route for preparing graphene-based composites comprising of metal oxide nanoparticles and graphene. A graphene nanosheet-bismuth oxide composite as electrode materials of supercapacitors was firstly synthesized by thermally treating the graphene-bismuth composite, which was obtained through simultaneous solvothermal reduction of the colloidal dispersions of negatively charged graphene oxide sheets in N,N-dimethyl formamide (DMF) solution of bismuth cations at 180 °C. The morphology, composition, and microstructure of the composites together with pure graphite oxide, and graphene were characterized using powder X-ray diffraction (XRD), FT-IR, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetry and differential thermogravimetry (TG-DTG). The electrochemical behaviors were measured by cyclic voltammogram (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS). The specific capacitance of 255 F g⁻¹ (based on composite) is obtained at a specific current of 1 A g⁻¹ as compared with 71 F g⁻¹ for pure graphene. The loaded-bismuth oxide achieves a specific capacitance as high as 757 F g⁻¹ even at 10 A g⁻¹. In addition, the graphene nanosheet-bismuth oxide composite electrode exhibits the excellent rate capability and well reversibility.     

Oxygen transport in composite mediated biocathodes

A numerical simulation of an enzyme-catalyzed oxygen cathode is presented and applied to the analysis of transport limitations in operating electrodes, with the goal of predicting the limits of obtainable cathode current density. Based on macrohomogeneous and thin-film theories, and accounting for dual-substrate enzyme kinetics, the one-dimensional model predicts a maximum current density of about 9.2 mA cm⁻² at 0.6 V (SHE) for a 300 μm thick electrode operating oxygen-saturated pH 5 buffer at 37 °C and relying on diffusion of dissolved oxygen alone. However, by introducing gas-phase diffusive transport, or alternatively a convective, flow-through approach, the model predicts that electrodes of identical thickness may provide current densities up to 60 mA cm⁻² in air and exceeding 100 mA cm⁻² in pure O₂. Such performance would move enzyme electrodes closer to practical implementation in implantable power devices and other low-temperature fuel cells such as direct methanol fuel cells.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Sensitive determination of Cd and Pb by differential pulse stripping voltammetry with in situ bismuth-modified zeolite doped carbon paste electrodes

Here we investigated the analytical performances of the bismuth-modified zeolite doped carbon paste electrode (BiF-ZDCPE) for trace Cd and Pb analysis. The characteristics of bismuth-modified electrodes were improved greatly via addition of synthetic zeolite into carbon paste. To obtain high reproducibility and sensitivity, optimum experimental conditions for bismuth deposition were studied. Voltammetric responses of the BiF-ZDCPEs prepared with different ratios of zeolite, carbon powder, and silicone, were examined under same conditions. The in situ plated (zeolite/graphite powder/silicone, 10/190/80 w/w) BiF-ZDCPEs exhibited the most sensitive response to Cd and Pb in 0.10 M acetate buffer (pH 4.5). The detection limits of the modified electrode were 0.08 μg L⁻¹ for Cd(II) and 0.10 μg L⁻¹ for Pb(II) based on three times the standard deviation of the baseline with a preconcentration time of 120 s under optimal conditions, respectively. The modified electrode showed well linear response to both Cd(II) and Pb(II) over the concentration range from 1.0 to 20.0 μg L⁻¹. The BiF-ZDCPEs were successfully applied to the determination of Cd(II) and Pb(II) in real samples, and the results were in agreement with those of atomic absorption spectroscopy (AAS).     

Electrochemical decomposition of CO2 and CO gases using porous yttria-stabilized zirconia cell

Electrochemical decomposition of CO₂ and CO gases using a porous cell of Ru-8 mol% yttria-stabilized zirconia (YSZ) anode/porous YSZ electrolyte/Ni–YSZ cathode system at 400–800 °C was studied by analyzing the flow rate and composition of outlet gas, current density, and phases and elementary distribution of the electrodes and electrolyte. A part of CO₂ gas supplied at 50 ml/min was decomposed to solid carbon and O₂ gas through the cell at the electric field strengths of 0.9–1.0 V/cm. The outlet gas at a flow rate of 3 ml/min included 61–63% CO₂ and 37–39% O₂ at 700–800 °C and the outlet gas at a flow rate of 50 ml/min included 73–96% (average 85%) CO₂ and 4–27% (average 15%) O₂ at 800 °C. On the other hand, the supplied CO gas was also decomposed to solid carbon, O₂ and CO₂ gases at 800 °C. The fraction of outlet gas at a flow rate of 50 ml/min during the CO decomposition at 800 °C for 5 h was 11–36% CO, 59–81% O₂ and 2–9% CO₂. The detailed decomposition mechanisms of CO₂ and CO gases are discussed. Both Ni metal in the cathode and porous YSZ grains under the DC electric field have the ability to decompose CO gas into solid carbon and O²⁻ ions or O₂ gas.     

Catalytic reduction of hydrogen peroxide at metal hexacyanoferrate composite electrodes and applications in enzymatic analysis

The electrocatalytic activity of various metal hexacyanoferrates (Mhcfs) (i) immobilized on graphite electrodes, and (ii) as components of a composite electrode was investigated with respect to the reduction of hydrogen peroxide. The flow-through working electrode was a thin layer consisting of a composite of Mhcf, graphite, and polymethylmetacrylate (PMMA) as a binder, sandwiched between two Plexiglas plates. Among the pure Mhcfs immobilized on a graphite electrode, iron(III) hexacyanoferrate (Prussian blue) exhibits the highest electrocatalytic effect, whereas in the composite electrodes chromium(III) hexacyanoferrate (Crhcf) shows the highest activity and best performance and reproducibility for the electrochemical reduction of H₂O₂. The Crhcf electrode provides a linear dependence on H₂O₂ concentration in the range 2.5 × 10⁻⁶ mol L⁻¹ (LOD) to 1 × 10⁻⁴ mol L⁻¹ (phosphate buffer, pH 7). The sensor was applied for the detection of H₂O₂ enzymatically produced by glucose oxidase. The optimal conditions for the peroxide injection were 2 min after the beginning of the reaction and 25 °C with a detection limit of 7.0 × 10⁻⁶ mol L⁻¹ for glucose.     

In situ preparation of Si3N4–TiN composite by pyrolysis of polytitanosilazane (PTSZ)

Si₃N₄–TiN composite powders were obtained by in situ pyrolysis of polytitanosilazane. Dense Si₃N₄–TiN composites were prepared by hot-pressing at 1800 °C under 20 MPa for 2 h without sintering additive. Crystallization of amorphous PTSZ powders occurred between 1400 and 1500 °C with major phases, α-Si₃N₄, β-Si₃N₄, and small amount of phase TiN. Mechanical properties and microstructure of Si₃N₄–TiN composites were characterized. The results showed that the mechanical strength was 620 MPa, the fracture toughness was 7.8 MPa m^1/2 and the Vickers hardness was 8.5 GPa. SEM analysis indicated that Si₃N₄–TiN composite possessed excellent fracture toughness because TiN grains produced by in situ pyrolysis were well dispersed in Si₃N₄ matrix.     

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Commercial nanoporous carbon RP-20 was activated with water vapor in the temperature range from 950 °C to 1150 °C. The XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ? 1150 °C. The first-order Raman spectra showed the absorption peak at 1582 cm⁻¹ and the disorder (D) peak at 1350 cm⁻¹. The low-temperature N₂ adsorption experiments were performed at −196 °C and a specific surface area up to 2240 m²g⁻¹ for carbon activated at T = 1050 °C was measured. The cell capacitance for two electrode activated nanoporous carbon system advanced up to 60 F g⁻¹ giving the specific capacitance ∼240 F g⁻¹ to one electrode nanoporous carbon ∣1.2 M (C₂H₅)₃CH₃NBF₄ + acetonitrile solution interface. A very wide region of ideal polarisability for two electrode system (∼3.2 V) was achieved. The low frequency limiting specific capacitance very weakly increases with the rise of specific area explained by the mass transfer limitations in the nanoporous carbon electrodes. The electrochemical characteristics obtained show that some of these materials under discussion can be used for compilation of high energy density and power density non-aqueous electrolyte supercapacitors with higher power densities than aqueous supercapacitors.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

Nano-sized Sm0.5Sr0.5CoO3−δ as the cathode for solid oxide fuel cells with proton-conducting electrolytes of BaCe0.8Sm0.2O2.9

Nano-sized Sm_0.5Sr_0.5CoO_3−δ (SSC) was fabricated onto the inner face of porous BaCe_0.8Sm_0.2O_2.9 (BCS) backbone by ion impregnation technique to form a composite cathode for solid oxide fuel cells (SOFCs) with BCS, a proton conductor, as electrolyte. The electro-performance of the composite cathodes was investigated as function of fabricating conditions, and the lowest polarization resistance, about 0.21 Ω cm² at 600 °C, was achieved with BCS backbone sintered at 1100 °C, SSC layer fired at 800 °C, and SSC loading of 55 wt.%. Impedance spectra of the composite cathodes consisted of two depressed arcs with peak frequency of 1 kHz and 30 Hz, respectively, which might correspond to the migration of proton and the dissociative adsorption and diffusion of oxygen, respectively. There was an additional arc peaking at 1 Hz in the Nyquist plots of a single cell, which should correspond to the anode reactions. With electrolyte about 70 μm in thickness, the simulated anode, cathode and bulk resistances of cells were 0.021, 0.055 and 0.68 Ω cm² at 700 °C, relatively, and the maximum power density was 307 mW cm⁻² at 700 °C.     

A polymer complex solution process for the synthesis and characterization of Ni–YSZ cermet material

Ni–YSZ cermets for SOFC anodes were prepared by the Pechini-type reaction route. The initial polymer precursors were prepared with different citric acid/ethylene glycol (CA/EG) molar ratios. The properties of the samples at different stages of the preparation procedure were evaluated with regard to thermal decomposition (TG–DTA), crystallite size (XRD), surface area (BET), sinterability and phase distribution (SEM). The results showed that an increase of CA and EG in the starting solution increased the final temperature of the thermal decomposition of gels from 340 °C to 382 °C, and the specific surface area of calcined NiO–YSZ powders from 10 m² g⁻¹ to 27 m² g⁻¹. In parallel the sinterability of the samples increased. A distinct increase of CA in the predominantly aqueous solution diminished the nickel grain size in the final Ni–YSZ material. A shift from aqueous to organic media further reduced the nickel-rich regions to around 0.2 μm.