The improvement of free-radical scavenging capacity of the phosphate medium electrosynthesized polyaniline

The oxidative polymerization of aniline on composite 2B pencil graphite was accomplished in phosphoric acid (H₃PO₄) containing 0.06 M calcium phosphate (Ca₃(PO₄)₂). The shifting of three pairs of redox peaks by 250 mV to the negative direction has increased antioxidant capacity of polyaniline (PAni). This was realised through reaction with 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical in methanol. The phosphate medium prepared PAni was a strong reducing agent and radical scavenger. Additionally, it was twice more effective than the one prepared in chloride medium.     

Influence of ionic liquids on the direct electrochemistry of glucose oxidase entrapped in nanogold-N,N-dimethylformamide-ionic liquid composite film

Glucose oxidase (GOD) immobilized in nanogold particles (NAs)-N,N-dimethylformamide (DMF) composite film on glassy carbon (GC) electrode exhibits a pair of quasi-reversible and unstable peaks due to the redox of flavin adenine dinucleotide (FAD) of GOD. When ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) or trihexyltetradecylphosphorium bis (trifluoromethylsulfony) (P_666,14 NTf₂) is introduced in the film, the peaks become small. But ILs 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) and 1-octyl-3-methylimidazolium hexafluorophate (OMIMPF₆) make the peaks large and stable. In different composite films the formal potential (E⁰′) of GOD is different. UV-vis spectra show that the GOD dispersed in these films almost retains its native structure and there are weak interactions between ILs and GOD. Electrochemical impedance spectra display that NAs can promote the electron transfer between FAD and GC electrode; and ILs can affect the electron transfer through interacting with GOD. The thermal stability of GOD entrapped in NAs-DMF-ILs composite films is also influenced by ILs, and it follows such order as: in NAs-DMF-OMIMPF₆ > in NAs-DMF-BMIMPF₆ ≈ in NAs-DMF-BMIMBF₄ > in NAs-DMF. In addition, GOD immobilized in NAs-DMF-OMIMPF₆ and NAs-DMF-BMIMPF₆ films shows good catalytic activity to the oxidation of glucose. The I_max of H₂O₂ and the apparent K_m (Michaelis-Menten constant) for the enzymatic reaction are calculated.     

Uncommon potential hysteresis in the Li/Li2xVO(H2−xPO4)2 (0 ≤ x ≤ 2) system

Physical and electrochemical investigations of vanadium phosphates, Li_2xVO(H_2−xPO₄)₂ (0 < x < 2), have been undertaken. H⁺/Li⁺ ionic exchange from VO(H₂PO₄)₂ to Li₂VO(HPO₄)₂ leads to grain decrepitation. Further ionic exchange toward formation of Li₄VO(PO₄)₂ lowers the symmetry. As inferred from potentiodynamic cycling correlated to ex situ and in situ X-ray diffraction (XRD), the system Li/Li₄VO(PO₄)₂ shows several phase transformations that are associated with thermodynamical potential hysteresis that span from roughly 15 mV to more than 1.8 V. Small hysteresis are associated with topotactic reactions and with V^V/V^IV and V^III/V^II redox couples. Large potential hysteresis values (>1 V) were observed when oxidation of V^III to V^IV is involved.     

Bioethanol production from corn meal by simultaneous enzymatic saccharification and fermentation with immobilized cells of Saccharomyces cerevisiae var. ellipsoideus

The simultaneous enzymatic saccharification and fermentation (SSF) of corn meal using immobilized cells of Saccharomycescerevisiae var. ellipsoideus yeast in a batch system was studied. The yeast cells were immobilized in Ca-alginate by electrostatic droplet generation method. The process kinetics was assessed and determined and the effect of addition of various yeast activators (mineral salts: ZnSO₄ · 7H₂O and MgSO₄ · 7H₂O, and vitamins: Ca-pantothenate, biotin and myo-inositol) separately or mixed, was investigated. Taking into account high values of process parameters (such as ethanol concentration, ethanol yield, percentage of the theoretical ethanol yield, volumetric productivity and utilized glucose) and significant energy savings the SSF process was found to be superior compared to the SHF process. Further improvement in ethanol production was accomplished with the addition of mineral salts as yeast activators which contributed to the highest increase in ethanol production. In this case, the ethanol concentration of 10.23% (w/w), percentage of the theoretical ethanol yield of 98.08%, the ethanol yield of 0.55 g/g and the volumetric productivity of 2.13 g/l·h were obtained.     

Synthesis and electrochemical properties of Co-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

Co-doped Li₃V_2−xCo_x(PO₄)₃/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li₃V_2−xCo_x(PO₄)₃/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li₃V_2−xCo_x(PO₄)₃. XPS studies also revealed that V⁴⁺ and V³⁺ ions were present in the Co²⁺-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li₃V_2−xCo_x(PO₄)₃/C compounds showed that the voltage peaks associated with the extraction of three Li⁺ ions shifted to higher voltages with an increase in Co content, and when the Co²⁺-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li₃V₂(PO₄)₃ phase. For the Li₃V_1.85Co_0.15(PO₄)₃/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li₃V₂(PO₄)₃) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co²⁺into V sites should be favorable for the structural stability of Li₃V_2−xCo_x(PO₄)₃/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li⁺ extraction/insertion, thus resulting in the improvement of cell cycling ability.     

Electrochemical synthesis of poly(N-methylaniline) on an iron electrode and its corrosion performance

Synthesis of poly(N-methylaniline) (PNMA) on pure iron and Pt electrodes was carried out from aqueous 0.3 M oxalic acid solution containing 0.1 M N-methylaniline (NMA) by potentiodynamic and galvanostatic techniques. It was found that when compared to polyaniline (PAni) and its ring- and N-ethyl-substituted derivatives, PNMA can be electrosynthesized with lower upper scanning potential (upper potential limit, E_upp) of 0.8 V vs. saturated calomel electrode (SCE) on an Fe electrode. PNMA coatings were characterized by electrochemical, scanning electron microscopy (SEM) and FTIR techniques. Linear anodic potentiodynamic polarization results proved that increasing the acidity of the polymerization solution causes more effective protection against corrosion in 0.5 M H₂SO₄ medium for PNMA. Moreover, PNMA exhibited similar protective properties with PAni under the same corrosion test conditions. Tafel test results reveal that the PNMA coating appears to enhance protection for iron in 0.5 M NaCl and 0.1 M HCl solutions. According to EIS results, the PNMA coating is able to offer protection to Fe electrodes in NaCl compared to that in HCl medium over a long immersion period.     

Processing and performance of solid oxide fuel cell with Gd-doped ceria electrolyte

Fuel Cell performance was measured at 792-1095 K for Ni-GDC (Gd-doped ceria) anode-supported GDC film (60 μm thickness) with a (La_0.8Sr_0.2)(Co_0.8Fe_0.2)O₃ cathode using H₂ fuel containing 3 vol% H₂O. A maximum power density, 436 mW/cm², was obtained at 1095 K. The electrical conductivity of GDC electrolyte in N₂ atmosphere of 10⁻¹⁵-10⁰ Pa oxygen partial pressures (Po₂) at 773-1073 K was independent of Po₂, which indicated the diffusion of oxide ions. The conductivity of GDC in H₂O/H₂ atmosphere increased because of the further formation of electrons due to the dissociation of hydrogen in GDC (H₂ → 2H⁺ + 2e⁻). The hole conductivity was observed at 873 K in Po₂ = 10⁰-10⁴ Pa. The key factors in increasing power density are the increase of open circuit voltage and the suppression of H₂ fuel dissolution in GDC electrolyte. These are controlled by the cathode material and Gd-dopant composition.     

Composite effects of silicon pyrophosphate as a supporting matrix for CsH5(PO4)2 electrolytes at intermediate temperatures

The proton-conductive electrolytes of CsH₅(PO₄)₂/SiP₂O₇ composites were synthesized, and composite effects of silicon pyrophosphate as a supporting matrix at intermediate temperatures were investigated by comparing the properties of CsH₅(PO₄)₂/SiO₂ composite. Although both composites showed similar thermal stability, the temperature dependence of the conductivity was quite different each other; the conductivity of the composite electrolyte of CsH₅(PO₄)₂/SiP₂O₇ was about one-order magnitude higher at every temperature investigated and the maximum conductivity achieved was 116 mS cm⁻¹ at 230 °C. These results suggested that the interfacial interaction between the proton-conductor phase of CsH₅(PO₄)₂ and the matrix of SiP₂O₇ played an important role in the proton conduction mechanism.     

Electrochemical behaviour of (111) B-Doped Polycrystalline Diamond: Morphology/surface conductivity/activity assessed by EIS and CS-AFM

Electrochemical activity, morphology and surface electrical conductivity of Boron-Doped Polycrystalline Diamond films prepared by MPCVD have been investigated. Heterogeneous apparent rate constants of three different redox systems, [Fe(CN)₆]^3−/4−, [IrCl₆]^2−/3− and [Ru(NH₃)₆]^3+/2+ have been measured by both Cyclic Voltammetry and Electrochemical Impedance Spectroscopy on < 100 > textured films with a predominance of (111) faces: first measurements have been done with [Fe(CN)₆]^3−/4− only on as grown samples, and secondly after a mild electrochemical pretreatment the three redox systems have been investigated. “As-grown” samples showed a moderate average activity which was related to the presence of a minority of electronically conducting areas among insulating zones. Electrochemical treatment in neutral conditions substantially increased the activity and heterogeneous apparent rate constants k_app for the three couples were measured in the range of 10^− 2 cm s^− 1 with a good stability in time. Current-sensing AFM images performed ex situ showed that the electrochemically pre-treated material presented a high superficial conductivity whereas the grown sample showed major area of low conductivity.     

Effect of A+ (A = Li,Na and K) co-doping on enhancing the luminescence of Ca5(PO4)2SiO4:Eu3+ red-emitting phosphors as charge compensator

A series of Ca_5-x(PO₄)₂SiO₄:xEu³⁺ red-emitting phosphors were synthesized through solid-state reaction, and alkali metal ions A⁺ (A = Li, Na and K) were co-doped in Ca₅(PO₄)₂SiO₄:Eu³⁺ to improve its luminescence property. The impacts of synthesis temperature, luminescence center Eu³⁺ concentration and charge compensator A⁺ on the structure and luminescence property of samples were studied in detail. X-ray diffraction results indicated that prepared Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ had a standard Ca₅(PO₄)₂SiO₄ structure with space group P6₃/m. Under the excitation of 392 nm, Ca₅(PO₄)₂SiO₄:Eu³⁺ phosphors showed a red emission consisting of several emission peaks at 593 nm, 616 nm and 656 nm, relevant to ⁵D₀→⁷F₁, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ electron transitions of Eu³⁺ ions, respectively. Luminescence intensity and lifetime of Ca₅(PO₄)₂SiO₄:Eu³⁺ can be significantly enhanced through co-doping alkali metal ion A⁺, which play an important role as charge compensator. The results suggest that Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ red phosphors with excellent luminescence property are expectantly served as red component for white light-emitting diodes excited by near-ultraviolet.     

Effect of double doping on crystal structure and electrical conductivity of CaO and WO3-doped Bi2O3

The atomic arrangement of WO₃-doped Bi₂O₃ was found similar to that of the fluorite structure. However, the electrical conductivity of WO₃-doped Bi₂O₃ is significantly lower than that of commonly used Y₂O₃-doped Bi₂O₃. The structure and electrical conductivity of samples formulated as (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi₂O₃·2WO₃. Therefore, (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO₄ for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10⁻² S cm⁻¹ at 700 °C for x = 0.1 that is higher than that of Ca-free (W_0.15Bi_0.85)₂O_3.45. The higher conductivity of (Ca_0.1W_0.15Bi_0.75)₂O_3.35 than (W_0.15Bi_0.85)₂O_3.45 may result from the higher anion vacancy concentration and more symmetrical structure.     

Continuous salt precipitation and separation from supercritical water. Part 1: Type 1 salts

The precipitation and separation performance of various binary type 1 salt-water mixtures was systematically studied for the first time in a continuously operated laboratory plant. The aim was to find a field of operation for the salt separator where salts can be separated with high efficiency. Experiments with aqueous solutions of the salts NaNO₃, KNO₃, Ca(NO₃)₂, K₂CO₃, KHCO₃, (NH₄)₂CO₃, K₃PO₄, K₂HPO₄, KH₂PO₄, NaCl, KCl, NH₄Cl and (NH₄)₂SO₄ were carried out at 30 ± 0.5 MPa varying the salt separator temperature from sub-critical to supercritical. For most of these salts separation efficiencies ranging from 80 to 97% were obtained. For the nitrates the separation efficiency increased in the order NaNO₃ < KNO₃ < Ca(NO₃)₂, whereas for potassium salts the separation efficiency of the phosphates was significantly higher than that of KNO₃. Considerable hydrolysis of the phosphate and the hydrogen phosphate salts in supercritical water was found, although this had no negative influence on the phosphate separation efficiency. It was found that the ammonium salts decompose in supercritical water, probably to ammonia and the corresponding mineral acids, leading to reduced separation of the ammonia due to its high solubility in supercritical water.     

A promising sol-gel route based on citric acid to synthesize Li3V2(PO4)3/carbon composite material for lithium ion batteries

Li₃V₂(PO₄)₃/carbon composite material was synthesized by a promising sol-gel route based on citric acid using V₂O₅ powder as a vanadium source. Citric acid acts not only as a chelating reagent but also as a carbon source, which enhance the conductivity of the composite material and hinder the growth of Li₃V₂(PO₄)₃ particles. The structure and morphology of the sample were characterized by TG, XRD and TEM measurements. XRD results reveal that Li₃V₂(PO₄)₃/carbon was successfully synthesized and has a monoclinic structure with space group P2₁/n. TEM images show Li₃V₂(PO₄)₃ particles are about 45 nm in diameter embeded in carbon networks. Galvanostatic charge/discharge and cyclic voltammetry measurements were used to study its electrochemical behaviors which indicate the reversibility of the lithium extraction/insertion processes. Li₃V₂(PO₄)₃/carbon performed in a voltage window (3.0-4.8 V) exhibits higher discharge capacity, better cycling stability and its discharge capacity maintains about 167.6 mAh/g at a current density of 28 mA/g after 50 cycles.     

Direct electrochemistry and electrocatalysis of cytochrome c based on chitosan-room temperature ionic liquid-carbon nanotubes composite

A robust and effective composite film combined the benefits of room temperature ionic liquid (RTIL), chitosan (Chi) and multi-wall carbon nanotubes (MWNTs) was prepared. Cytochrome c (Cyt c) was successfully immobilized on glassy carbon electrode (GCE) surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Cyt c were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Cyt c was obtained in 0.1 mol L⁻¹ pH 7.0 phosphate buffer solution (PBS), indicating the Chi-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0 × 10⁻⁶ to 2.6 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ (S/N = 3). The apparent Michaelis-Menten constant (K_m) was calculated to be 0.45 ± 0.02 mmol L⁻¹. Moreover, the modified electrode displayed a rapid response (5 s) to H₂O₂, and possessed good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Impedance analysis of Sr-substituted CePO4 with mixed protonic and p-type electronic conduction

Members of the solid-solution series Ce_1−xSr_xPO_4−δ (x = 0, 0.01, 0.02) with mixed protonic and electronic transport have been synthesized by a nitrate-decomposition method followed by sintering at 1450 °C. Impedance spectroscopy is employed to estimate the bulk electrical conductivity in wet (∼0.03 atm) and dry atmospheres of O₂ and 10%H₂:90%N₂. Conductivity increases with dopant concentration (x), oxygen partial pressure (pO₂) and water vapour partial pressure (pH₂O) reaching ∼3.5 × 10⁻³ S cm⁻¹ at 600 °C for x = 0.02 in wet O₂. Activation energies (E_a) for the bulk conductivity of Ce_0.98Sr_0.02PO_4−δ below 650 °C are 0.44 and 0.78 eV for wet oxidising and wet reducing conditions, respectively. A moderate but positive pO₂⁺ⁿ power-law dependence (n < 1/10) of conductivity is exhibited in the pO₂ range 10^−2.5 to 10⁻¹ atm, consistent with mixed ionic and p-type electronic transport. Thermogravimetric analysis indicates that the Sr-doped materials are stable in a CO₂ atmosphere in the temperature range 25–1200 °C.     

Electrochemical incineration of p-cresol and o-cresol in the filter-press-type FM01-LC electrochemical cell using BDD electrodes in sulfate media at pH 0

This work shows a comparative study of the incineration of 2-mM p-cresol and o-cresol in 1 M-H₂SO₄ in aqueous media. Microelectrolysis studies indicated that both the p-cresol and o-cresol oxidation were carried out via hydroxyl radicals (OH) formed by water oxidation in the boron-doped diamonds (BDD)-H₂O-H₂SO₄-p-cresol and o-cresol interface. In both cases, the potential and current density ranges, where great amounts of OH are formed, were between 2.3 V ≤ E ≤ 2.75 V versus SHE and J = 10 mA cm⁻². Electrolyses in an undivided FM01-LC reactor were performed at different Reynolds values 27,129 ≤ Re ≤ 42,631, and at J = 10 mA cm⁻². For p-cresol and o-cresol, the rate of degradation was slow, however it increases slightly as a function of the Re, indicating that the oxidation involves a complex pathway; current efficiency also rises as a function of the Re. For p-cresol, the mineralization at Re = 42,631 reached 90%, with 71% current efficiency and an energy consumption of 7.84 kWh m⁻³; whereas o-cresol was mineralized to 84%, with 67% current efficiency and an energy consumption of 6.56 kWh m⁻³. The results obtained in this work demonstrated that o-cresol is more recalcitrant than p-cresol.     

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite and its application for electrochemical supercapacitor

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO₂/P(An-co-oAs)] was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the MnO₂/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The MnO₂/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near 100 times greater than that of its pristine MnO₂ (3.5 × 10⁻⁷ S cm⁻¹). The specific capacitance of the MnO₂/P(An-co-oAs) nanocomposite reached 262 F g⁻¹ in 1 M Na₂SO₄ at a current density of 1 A g⁻¹, which was significantly higher than that of either of its two pristine materials [MnO₂ (182 F g⁻¹) or P(An-co-oAs) (127 F g⁻¹)] owing to the synergic effect between the two pristine components. The fabrication mechanism of the nanocomposite was also proposed and discussed in this paper.     

Characterization of permselective coatings electrosynthesized on Pt-Ir from the three phenylenediamine isomers for biosensor applications

The permeability of polymers, electrosynthesized at neutral pH on Pt-Ir cylinders from each of the three isomers of phenylenediamine (oPD, mPD and pPD), to H₂O₂ (signal transduction molecule in many oxidase-based biosensors) and ascorbic acid (AA, archetypal interference species in biological applications of biosensors) was measured, and used to determine the permselectivity of the three polymers. PmPD was the coating with the greatest permselectivity for H₂O₂ over AA, for low concentrations of AA. For AA levels greater than 200 μM, however, poly-ortho-phenylenediamine (PoPD) was superior. Furthermore, stability studies indicated that the permselectivity of PmPD degraded rapidly, even after 1 day, supporting the choice of PoPD as the permselective membrane for biosensor implantation where AA levels are high, such as in brain monitoring. A variety of techniques were used to gain further insight into the PPD layers, specifically electrochemical quartz crystal microbalance, mass spectrometry and scanning electron microscopy. Together these studies indicate that PmPD forms the thickest layer (∼15 nm) and is the least soluble of the polymers, that the PoPD layer is ∼4 nm thick and may consist mostly of tetramers, while PpPD is the thinnest (∼3 nm) and appears to consist of trimers.     

Electrical conductivity of samarium-ytterbium zirconate ceramics

(Sm_1 − xYb_x)₂Zr₂O₇ (0 ≤ x ≤ 1.0) ceramic powders were prepared by chemical-coprecipitation and calcination method, and were pressureless-sintered at 1973 K for 10 h to fabricate dense bulk materials. (Sm_1 − xYb_x)₂Zr₂O₇ has a single phase with a pyrochlore or defect fluorite structure, depending mainly upon the Yb content. They are found to be pyrochlores for 0 ≤ x ≤ 0.1, and defect fluorites for 0.3 ≤ x ≤ 1.0. The electrical conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ was investigated by complex impedance spectroscopy over a frequency range of 200 Hz to 20 MHz from 723 to 1173 K in air. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ ceramics gradually increases with increasing temperature. A decrease of about one order of magnitude in grain conductivity is found at all temperature levels when the Yb content increases from x = 0.1 to x = 0.3. The electrical conductivities of defect fluorite-type materials are lower than those of pyrochlore-type materials in (Sm_1 − xYb_x)₂Zr₂O₇ system, whereas activation energies for the conduction process increase monotonically as the structure becomes disordered.