Anode performance of Mn-doped ceria–ScSZ for solid oxide fuel cell

The 70 wt.% Mn-doped CeO₂ (MDC)-30 wt.% Scandia-stabilized zirconia (ScSZ) composites are evaluated as anode materials for solid oxide fuel cells (SOFCs) in terms of chemical compatibility, thermal expansion coefficient, electrical conductivity, and fuel cell performance in H₂ and CH₄. The conductivity of MDC10 (10 mol.% Mn-doping), MDC20, and CeO₂ are 4.12, 2.70, and 1.94 S cm⁻¹ in H₂ at 900 °C. With 10 mol.% Mn-doping, the fuel cells performances improve from 166 to 318 mW cm⁻² in H₂ at 900 °C. The cell with MDC10–ScSZ anode exhibits a better performance than the one with MDC20–ScSZ in CH₄, the maximum power density increases from 179 to 262 mW cm⁻². Electrochemical impedance spectra indicate that the Mn doping into CeO₂ can reduce the ohmic and polarization resistance, thus leading to a higher performance. The results demonstrate the potential ability of MDC10–ScSZ composite to be used as SOFCs anode.     

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Thermal and dielectric properties of PEO/EC/Pr4N+I− polymer electrolytes for possible applications in photo-electro chemical solar cells

The anion-conducting polymer electrolyte polyethylene oxide (PEO)/ethylene carbonate (EC)/Pr₄N⁺I⁻/I₂ is a candidate material for fabricating photo-electrochemical (PEC) solar cells. Relatively high ionic conductivity values are obtained for the plasticized electrolytes; at room temperature, the conductivity increases from 7.6 × 10⁻⁹ to 9.5 × 10⁻⁵ S cm⁻¹ when the amount of EC plasticizer increases from 0% to 50% by weight. An abrupt conductivity enhancement occurs at the melting of the polymer; above the melting temperature, the conductivity can reach values of the order of 10⁻³ S cm⁻¹. The melting temperature decreases from 66.1 to 45.1 °C when the EC mass fraction is increased from 0% to 50%, and there is a corresponding reduction in the glass transition temperature from −57.6 to −70.9 °C with the incorporation of the plasticizer. The static dielectric constant values, , increase with the mass fraction of plasticizer, from 3.3 for the unplasticized sample to 17.5 for the 50% EC sample. The dielectric results show only small traces of ion-pair relaxations, indicating that the amount of ion association is low. Thus, the iodide ion is well dissociated, and despite its large size and relatively low concentration in these samples, the iodide ion to ether oxygen ratio is 1:68, a relatively efficient charge carrier. A further enhancement of the ionic conductivity, especially at lower temperatures, is however desired for these applications.     

A polymer electrolyte containing ionic liquid for possible applications in photoelectrochemical solar cells

Various iodide ion conducting polymer electrolytes have been studied as candidate materials for fabricating photoelectrochemical (PEC) solar cells and energy storage devices. In this study, enhanced ionic conductivity values were obtained for the ionic liquid tetrahexylammonium iodide containing polyethylene oxide (PEO)-based plasticized electrolytes. The analysis of thermal properties revealed the existence of two phases in the electrolyte, and the conductivity measurements showed a marked conductivity enhancement during the melting of the plasticizer-rich phase of the electrolyte. Annealed electrolyte samples showed better conductivity than nonannealed samples, revealing the existence of hysteresis. The optimum conductivity was shown for the electrolytes with PEO:salt = 100:15 mass ratio, and this sample exhibited the minimum glass transition temperature of 72.2 °C. For this optimum PEO to salt ratio, the conductivity of nonannealed electrolyte was 4.4 × 10⁻⁴ S cm⁻¹ and that of the annealed sample was 4.6 × 10⁻⁴ S cm⁻¹ at 30 °C. An all solid PEC solar cell was fabricated using this annealed electrolyte. The short circuit current density (I _SC), the open circuit voltage (V _OC), and the power conversion efficiency of the cell are 0.63 mA cm⁻², 0.76 V, and 0.47% under the irradiation of 600 W m⁻² light.     

Development of activated carbon from vine shoots by physical and?chemical activation methods. Some insight into activation mechanisms

Activated carbons (ACs) are prepared from vine shoots (VS) by the method of physical activation in air, CO₂ and steam atmospheres and by the method of chemical activation with H₃PO₄, ZnCl₂ and KOH aqueous solutions. The ACs were characterized texturally by N₂ adsorption at −196 °C, mercury porosimetry, and density measurements. The method of chemical activation has been proved to be more effective than the method of physical activation to prepare ACs with a well-developed porosity. ACs with high micro- and mesopore volumes are prepared with ZnCl₂ and H₃PO₄. Using ZnCl₂, the volume of micropores is 0.62 cm³ g⁻¹ and the volume of mesopores is 0.81 cm³ g⁻¹. A greater development of macroporosity is obtained by KOH activation. The volume of macropores is as high as 1.13 cm³ g⁻¹ for the resulting AC. Yield of the process of preparation of the ACs is low for the method of chemical activation. Some insights into the performance of the activating agents in the activation process are provided.     

Fabrication of TiO2/Ti nanotube electrode and the photoelectrochemical behaviors in NaCl solutions

Titanium oxide nanotube electrodes were successfully prepared by anodic oxidation on pure Ti sheets in 0.5 wt.% NH₄F + 1 wt.% (NH₄)₂SO₄ + 90 wt.% glycerol mixed solutions. Nanotubes with diameter 40–60 nm and length 7.4 μm were observed by field emission scanning electron microscope. The electrochemical and photoelectrochemical characteristics of TiO₂ nanotube electrode were investigated using linear polarization and electrochemical impedance spectroscopy techniques. The open-circuit potential dropped markedly under irradiation and with the increase of Cl⁻ concentrations. A saturated photocurrent of approximately 1.3 mA cm⁻² was observed under 10-W low-mercury lamp irradiation in 0.1 M NaCl solution, which was much higher than film electrode. Meanwhile, the highest photocurrent in NaCl solution implied that the photogenerated holes preferred to combine with Cl⁻. Thus, a significant synergetic effect on active chlorine production was observed in photoelectrocatalytic processes. Furthermore, the generation efficiency for active chlorine was about two times that using TiO₂/Ti film electrode by sol–gel method. Finally, the effects of initial pH and Cl⁻ concentration were also discussed.     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Characteristics of methyl cellulose-NH4NO3-PEG electrolyte and application in fuel cells

We report the viability of methyl cellulose (MC) as a membrane in a polymer electrolyte membrane fuel cell (PEMFC). Methyl cellulose serves as the polymer host, ammonium nitrate (NH₄NO₃) as the doping salt and poly(ethylene glycol) (PEG) as plasticizer. Conductivity measurement was carried out using electrochemical impedance spectroscopy. The room temperature conductivity of pure MC film is ( 3.08±0.63 ) ×10 ^{- 11}S cm ^{- 1} \left( {{3}.0{8}\pm 0.{63}} \right) \times {1}{0^{ - {11}}}{\hbox{S}}\,{\hbox{c}}{{\hbox{m}}^{ - {1}}} . The conductivity increased to ( 2.10±0.37 ) ×10 ^{- 6}S cm ^{- 1} \left( {{2}.{1}0\pm 0.{37}} \right) \times {1}{0^{ - {6}}}{\hbox{S}}\,{\hbox{c}}{{\hbox{m}}^{ - {1}}} on addition of 25 wt.% NH₄NO₃. By adding 15 wt.% of PEG 200 to the highest conducting sample in the MC-NH₄NO₃ system, the conductivity was further raised by two orders of magnitude to ( 1.14±0.37 ) ×10 ^{- 4}S cm ^{- 1} \left( {{1}.{14}\pm 0.{37}} \right) \times {1}{0^{ - {4}}}{\hbox{S}}\,{\hbox{c}}{{\hbox{m}}^{ - {1}}} . The highest conducting sample containing 15 wt.% PEG was used as membrane in PEMFC and was operated at room and elevated temperatures. From voltage-current density characteristics, the short circuit current density was 31.52 mA cm⁻² at room temperature (25 °C).     

In situ formation of polyethylene glycol–titanium complexes as solvent-free electrolytes for electrochromic device application

Transparent and ionic conductive polymeric electrolytes have been prepared through sol–gel method by adding titanium isopropoxide into an acidic polyethylene glycol (PEG) solution. After hydrolysis and condensation processes, new associations between titanium cations and ether oxygen atoms of PEG have been formed according to Fourier-transform infrared spectroscopy. Thermogravimetric analysis results of these hybrid materials indicate a better thermal stability with a less polydispersion of the molecular mass distribution in comparison with PEG. For the purpose of electrochromic or photoelectrochromic device applications, LiI was added into the hybrid materials to form solvent-free polymeric electrolytes. Optical transmittance spectra of these electrolytes show a red shift of the cutoff wavelength as a function of titanium isopropoxide percentage in the original sol–gel solutions. It is also observed that the amount of hydroxyl groups in the hybrid materials was reduced in comparison with the PEG one. This makes electrical conductivity of the hybrid electrolytes with LiI salt insensitive to humidity and solvents, which was about 2 × 10^-4 Ω⁻¹ cm⁻¹ at room temperature. A solid WO₃-based electrochromic device with the hybrid electrolyte keeps the same optical transmittance value after 1,000 cycles of switching polarization potentials between −1 and +1 V.     

Inorganic-based sol–gel synthesis of nano-structured LiFePO4/C composite materials for lithium ion batteries

An inorganic and non-toxic compounds combination of FeCl₂·4H₂O, Li₂CO₃ and H₃PO₄ was chosen to synthesize homogeneous nano-structured LiFePO₄/C composite material via a simplified sol–gel route. The dependency of the physicochemical properties and the corresponding electrochemical responses on the residual carbon content were investigated in details. Rietveld refinement of X-ray diffraction measurement and X-ray photoelectron spectroscopy analysis confirmed the feasibility of preparing pure LiFePO₄ phase via this approach. With increasing amount of residual carbon, the particles size gradually decreased and the bulk electrical conductivity monotonically increased. However, the higher level of residual carbon would bring disadvantageous impact on the lithium ion diffusion. Due to high electrical conductivity, controlled particle size and suitable microstructure, the sample with 4.5 wt.% residual carbon exhibited stable cycling performance and delivered high discharge capacity of 163, 119 and 108 mA h g⁻¹ at 0.1 C, 5 C and 10 C, respectively.     

Laser Raman and conductivity studies of plasticized polymer electrolyte P(ECH-EO):propylenecarbonate:<Emphasis Type="Italic">γ</Emphasis>-butyrolactone:LiClO<Subscript>4</Subscript>

The plasticized polymer electrolytes composed of poly(epichlorohydrin-ethyleneoxide) (P(ECH-EO)) as host polymer, lithium perchlorate (LiClO₄) as salt, γ-butyrolactone (γ-BL), and propylene carbonate (PC) as plasticizer have been prepared by simple solution casting technique. The effect of mixture of plasticizers γ-BL and PC on conductivity of the polymer electrolyte P(ECH-EO):LiClO₄ has been studied. The band at 457 cm⁻¹ in the Raman spectra of plasticized polymer electrolyte is attributed to both the ring twisting mode of PC and the perchlorate ν ₂(ClO₄⁻) bending. The maximum conductivity value is observed to be 4.5 × 10⁻⁴ S cm⁻¹ at 303 K for 60P(ECH-EO):15PC:10γ-BL:15LiClO₄ electrolyte system. In the present investigation, an attempt has been made to correlate the Raman and conductivity data.     

Magnesium ion-conducting gel polymer electrolytes dispersed with fumed silica for rechargeable magnesium battery application

Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity of ∼1.1 × 10⁻² S cm⁻¹ at ∼25 °C with good thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO₃ as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g⁻¹ of MoO₃ for an initial ten charge–discharge cycles.     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Absolute integrated intensities of vapor-phase hydrogen peroxide (H2O2) in the mid-infrared at atmospheric pressure

We report quantitative infrared spectra of vapor-phase hydrogen peroxide (H₂O₂) with all spectra pressure-broadened to atmospheric pressure. The data were generated by injecting a concentrated solution (83%) of H₂O₂ into a gently heated disseminator and diluting it with pure N₂ carrier gas. The water vapor lines were quantitatively subtracted from the resulting spectra to yield the spectrum of pure H₂O₂. The results for the ν₆ band strength (including hot bands) compare favorably with the results of Klee et al. (J Mol. Spectrosc. 195:154, 1999) as well as with the HITRAN values. The present results are 433 and 467 cm^-2 atm⁻¹ (±8 and ±3% as measured at 298 and 323 K, respectively, and reduced to 296 K) for the band strength, matching well the value reported by Klee et al. (S = 467 cm⁻² atm⁻¹ at 296 K) for the integrated band. The ν₁ + ν₅ near-infrared band between 6,900 and 7,200 cm⁻¹ has an integrated intensity S = 26.3 cm⁻² atm⁻¹, larger than previously reported values. Other infrared and near-infrared bands and their potential for atmospheric monitoring are discussed.     

Polyethylene-supported poly(acrylonitrile-co-methyl methacrylate)/nano-Al2O3 microporous composite polymer electrolyte for lithium ion battery

Nano-Al₂O₃ was doped in poly(acrylonitrile-co-methyl methacrylate) (P(AN-co-MMA)), and polyethylene(PE)-supported P(AN-co-MMA)/nano-Al₂O₃ microporous composite polymer electrolyte (MCPE) was prepared. The performances of the prepared MCPE for lithium ion battery use, including ionic conductivity, electrochemical stability, interfacial compatibility, and cyclic stability, were studied by scanning electron spectroscopy, linear sweep voltammetry, and electrochemical impedance spectroscopy. It is found that the nano-Al₂O₃ significantly affects the MCPE performances. Compared to the MCPE without any nano-Al₂O₃, the MCPE with 10 wt.% nano-Al₂O₃ reaches its best performances. Its ionic conductivity is improved from 2.0 × 10⁻³ to 3.2 × 10⁻³ S cm⁻¹, its decomposition potential is enhanced from 5.5 to 5.7 V (vs Li/Li⁺), and its interfacial resistance on lithium is reduced from 520 to 160 Ω cm². Thus, the battery performance is improved.     

FAD-modified SiO2/ZrO2/C ceramic electrode for electrocatalytic reduction of bromate and iodate

SiO₂/ZrO₂/C carbon ceramic material with composition (in wt%) SiO₂ = 50, ZrO₂ = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image showed that ZrO₂ and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks of the material was 18 S cm⁻¹, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide (FAD) prepared by immersing the solid SiO₂/ZrO₂/C, molded as a pressed disk, inside a FAD solution (1.0 × 10⁻³ mol L⁻¹) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl) were: BrO₃ ⁻, lrr = 4.98 × 10⁻⁵–1.23 × 10⁻³ mol L⁻¹ and dl = 2.33 μmol L⁻¹; IO₃ ⁻, lrr = 4.98 × 10⁻⁵ up to 2.42 × 10⁻³ and dl = 1.46 μmol L⁻¹ for iodate.     

Electro-catalysis by immobilised human flavin-containing monooxygenase isoform 3 (hFMO3)

Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine (TMA), ammonia (NH₃), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant (K′_M) and apparent maximum current (I′_max) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol⁻¹ L cm⁻² for TMA, 43.3 ± 0.1 mA mol⁻¹ L cm⁻² for NH₃, 45.2 ± 2.2 mA mol⁻¹ L cm⁻² for TEA, and 39.3 ± 0.6 mA mol⁻¹ L cm⁻² for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3.     

Crystalline phase content and ionic conductivity correlation in LATP glass–ceramic

Li₂O–Al₂O₃–TiO₂–P₂O₅ (LATP) glass was fabricated by conventional melt quenching route. Glass transition temperature (T _g = 296 °C) and crystallization temperatures (T _C1,2) were obtained from thermal analysis. LATP glass was converted to glass–ceramic by heat treatment in the range 550–950 °C for 6 h. X-ray diffraction analysis revealed LiTi₂(PO₄)₃ as a major phase. Ionic conductivity increased monotonically with concentration, reaching a maximum of ~10⁻⁴ S/cm. AlPO₄ phase was detected in samples heat-treated above 850 °C. Its presence decreased the conductivity, suggesting LiTi₂(PO₄)₃ phase as main contributor to high ionic conductivity. NMR spectra confirmed the presence of mobile ⁷Li ions in the entire sample series and also gave some information on the structure and dynamics of conductivity.     

Electrochemical intercalation of O2− in CuAlO2 single crystal and photoelectrochemical properties

The delafossite CuAlO₂ single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹. The chronoamperometry showed an electrochemical O²⁻ insertion with a diffusion coefficient D _303K of 3.3 × 10⁻¹⁸ cm² s⁻¹. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol⁻¹. CuAlO₂ is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and a holes density (N _A) of 10¹⁶ cm⁻³. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration depth (12 μm).