High oxide ion conductivity in Fe and Mg doped LaGaO3 as the electrolyte of solid oxide fuel cells

La(Sr)Ga(Fe,Mg)O₃ exhibited the high oxide ion conductivity and the electrical power generating property of SOFC single cell using La_0.7Sr_0.3Ga_0.7Fe_0.2Mg_0.1O_3-δ (LSGFM) electrolyte was investigated in this study. The transport number of oxide ion is almost 0.8 in LSGFM and so open circuit potential (OCV) is as low as 0.8 V. OCV was strongly affected by anode materials and the highest OCV was achieved on Ni–Fe bimetallic anode. The extremely high power density was achieved by using LSGFM for electrolyte of SOFC. The maximum power densities of the cells can be elevated by coating with oxide ion conductor film at anode side. The maximum power density increased in the following order for coating film: LSGM > SDC > YSZ. The maximum power density of 197 and 100 mW/cm² can be achieved at 873 and 773 K, respectively, when LSGM film deposited on the anode side of LSGFM. Therefore, LSGFM can be used as electrolyte of SOFC operating at intermediate temperature.     

Electrical and structural investigations of perovskite structure reactively sputter deposited coatings

Sr(Zr_0.84Y_0.16)_0.91O_3 ? δ (SZY) and Ba(Zr_0.84Y_0.16)_0.96O_3 ? δ (BZY) protonic conductor coatings were co-sputter deposited from metallic targets in argon–oxygen reactive gas mixtures. The chemical and structural features were investigated by energy dispersive X-ray spectroscopy and X-ray diffraction, and their morphology was assessed by scanning electron microscopy of the surface and of brittle fracture cross sections. The electrical properties of the coating were determined by complex impedance spectroscopy as a function of temperature in air. Relationships are established between the electrical properties and the morphology of the coatings. The SZY as deposited coatings is amorphous and crystallises under the convenient perovskite structure after annealing treatment at 873 K under air. The BZY as deposited coatings is crystallised at 523 K in situ under perovskite structure and a further annealing treatment increases the grain size. Conductivities and activation energies of crystallised coatings were 3.1 · 10^? 5 S cm^? 1/2 · 10^? 5 S cm^? 1 and 0.65 eV/0.71 eV after stabilization at 773 K for strontium and barium zirconate, respectively.     

Recent progress in LaGaO3 based solid electrolyte for intermediate temperature SOFCs

Partial electronic and oxide ionic conduction in LaGaO₃ doped with Sr and Mg, Co for Ga site was studied with the ion blocking method. It was found that doping small amount of Co into Ga site is effective for elevating the oxide ion conductivity. However, it is seen that the partial electronic conduction monotonically increases with increasing Co amount and P_O2 at p–n transition was shifted to lower value. Even at X = 0.1, the oxide ion conductivity in LSGMC is still dominant. Calculation on the theoretical leakage of electrolyte of solid oxide fuel cells suggests that the highest efficiency of the electrolyte was achieved around 100 μm in thickness for La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O₃ (LSGMC). Preparation of LSGMC film on Ni–Sm_0.2Ce_0.8O₂ porous anode was studied with the colloidal spray method. In order to prevent the reaction between substrate and film, La doped CeO₂ was used for the interlayer film. In accordance with the theoretical calculation, open circuit potential of the cell using LSGMC film electrolyte with 40 μm thickness becomes much smaller than the theoretical value. However, fairly large maximum power density (0.21 W/cm²) can be achieved at 873 K and even at 773 K, the maximum power density of the cell as high as 0.12 W/cm² was exhibited on the SOFC using 40 μm thickness LSGMC electrolyte.     

Synthesis and ionic conductivity of polymeric ion gel containing room temperature ionic liquid and phosphotungstic acid

Composite electrolyte comprising phosphotungstic acid (PWA) filler and 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF₄) room temperature ionic liquid (RTIL) in poly(2-hydroxyethyl methacrylate) (PHEMA) matrix has been prepared. The polymer matrix was formed by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) monomers. BMImBF₄ was used as both ionic source and plasticizer, and PWA filler provided the proton conductivity in this system. The interactions and structure changes of the PHEMA-RTIL-PWA composites were investigated by Fourier transform infrared spectra, differential scanning calorimetry, and X-ray diffraction. PWA fillers maintained their Keggin structure within a limited range and enhanced the ionic conductivity of the composite electrolyte. The electrolyte with PWA at the 2 wt.% showed the highest ionic conductivity of 8 × 10^− 4 S cm^− 1 at room temperature and 96% relative humidity.     

ArF excimer laser deposition of wide-band gap solid electrolytes for thin film batteries

High quality solid electrolyte thin films was grown by pulsed laser deposition (PLD) using a high photon energy ArF excimer laser. Various amorphous thin films were successfully deposited on glass substrates from oxide targets; such as Li₃PO₄, LiBO₂, Li₂SiO₃, Li₂CO₃, Li₂SO₄, Li₂ZrO₃, LiAlO₂, Li₂WO₄ and Ohara glass ceramics. The morphology, optical property and ionic conductivity of these films were examined by optical microscope, UV–VIS spectroscopy and impedance analysis. Dramatic improvement of the film morphology was observed by using a high photon energy laser, while the broken film with many droplets was obtained by using lower ones. Ionic conductivity of the films was examined by impedance spectroscopy and dc polarization method. For example, an ionic conductivity of a Li₃PO₄ film was 4.6 × 10^? 6 S cm^? 1 at 25 °C with activation energy of 0.57 eV. Electronic conductivity measurements revealed that most of the films were pure lithium ion conductors, while a Li₂WO₄ film was a mixed conductor.     

Synthesis of ammonia at atmospheric pressure with Ce0.8M0.2O2−δ (M = La,Y, Gd,Sm) and their proton conduction at intermediate temperature

Ionic conduction in fluorite-type structure oxide ceramics Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) at temperature 400–800 °C was systematically studied under wet hydrogen/dry nitrogen atmosphere. On the sintered complex oxides as solid electrolyte, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in the solid states proton conducting cell reactor by electrochemical methods, which directly evidenced the protonic conduction in those oxides at intermediate temperature. The rate of evolution of ammonia in Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) is up to 7.2 × 10^− 9, 7.5 × 10^− 9, 7.7 × 10^− 9, 8.2 × 10^− 9 mol s^− 1 cm^− 2, respectively.     

Extraordinary fast oxide ion conductivity in La1.61GeO5−δ thin film consisting of nano-size grain

Thin films of La_1.61GeO_5−δ, a new oxide ionic conductor, were fabricated on dense polycrystalline Al₂O₃ substrates by a pulsed laser deposition (PLD) method and the effect of the film thickness on the oxide ionic conductivity was investigated on the nanoscale. The deposition parameters were optimized to obtain La_1.61GeO_5−δ thin films with stoichiometric composition. Annealing was found necessary to get crystalline La_1.61GeO_5−δ thin films. It was also found that the annealed La_1.61GeO_5−δ film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La_1.61GeO_5−δ thin films increased with the decreasing thickness as compared to that in bulk La_1.61GeO_5−δ. In particular, the improvement in conductivity of the film at low temperature was significant .The electrical conductivity of the La_1.61GeO_5−δ film with a thickness of 373 nm is as high as 0.05 S cm^− 1 (log(σ/S cm^− 1) = − 1.3) at 573 K.     

Modification of B-site doping of perovskite LaxSr1 − xFe1 − y−zCoyCrzO3 − δ oxide by Mg2+ ion

Co-doping B-site of perovskite oxide La_xSr_1 ? xCo_yFe_1 ? yO_3 ? δ (LSCFO) with Cr⁶⁺ and Mg²⁺ ions has been attempted in this research for revamping chemical stability and oxygen ionic conductivity of this mixed conducting oxide. It is known that partial substitution for B-site cations of LSCFO by Cr gives rise to a significant improvement on chemical and thermal stability of the perovskite oxide. On the basis of this doped structure, introduction of an immaterial dose of Mg²⁺ ion into its B-site results in a microstructure consisting of smaller grains with higher density than its precursor. Furthermore, the resulting perovskite oxide La_0.19Sr_0.8Fe_0.69Co_0.1Cr_0.2 Mg_0.01O_3 ? δ (LSFCCMO) displays higher O^2? conductivity than the solely Cr-doped LSCFO besides the improved chemical stability against reduction in 5% CH₄/He stream at 850 °C. A detailed examination of the oxidation states of B-site transition metal ions by XPS has also been conducted as a part of structural characterizations of LSFCCMO. The assessment of relative O^2? conductivity shows that the grain boundary area plays a more important role than the bulk phase in facilitating ion transport, but with comparable boundary areas the higher densification level is favorable.     

Mixed conductivity and oxygen permeability of doped Pr2NiO4-based oxide

Pr₂NiO₄-based oxide was studied as a new mixed electronic and oxide ionic conductor for the oxygen permeation membrane. It was found that Pr₂NiO₄ doped with Cu and Fe for Ni site exhibits the relatively high oxygen permeation rate. Doping second cation to Ni site is effective for improving the oxygen permeation rate and the trivalent cation seems to be effective for increasing the oxygen permeation rate. Among the examined cation, the highest oxygen permeation rate was obtained by doping 5 mol% Fe. The oxygen permeation rate was also significantly affected by the surface catalyst and the highest oxygen permeation rate of 80 μmol·min^− 1·cm^− 2 at 1273 K was achieved by using La_0.1Sr_0.9Co_0.9Fe_0.1O₃ for the surface catalyst. Since the electrical conductivity slightly decreased with decreasing P_O2 and it dropped significantly at P_O2 = 10^− 19 atm, chemical stability of Pr₂NiO₄-based oxide seems to be reasonably high. Application of this new mixed conductor for the oxygen permeation membrane under the CH₄ partial oxidation was also studied and it was confirmed that the oxygen permeation rate much improved under the CH₄ oxidation condition and this Pr₂NiO₄ can be used for the oxygen permeation membrane for the CH₄ partial oxidation.     

Synthesis and characterization of Ge and Sn(II) iodide-doped thioborate anhydrous proton conductors

Metal iodide-doped anhydrous proton conductors in the series xMI₂ + (1 − x)(HBS₂)₃, where M = Ge and Sn, have been prepared. These samples improve upon the anhydrous proton conductivity shown previously in the H₂S + B₂S₃ + GS_y series, where G = Si, Ge, and As, through a displacement reaction to incorporate HI into the materials. This is analogous to doping a silver halide salt into fast ion conducting chalcogenide glasses, such as AgI + Ag₂S + B₂S₃ + SiS₂, which results in a one to two orders of magnitude improvement in the ionic conductivity. The structural modification of the boroxol ring units in the thioboric acid is discussed based on the infrared and Raman spectroscopy. The DC conductivity, estimated from AC impedance spectra, of the metal iodide-doped (HBS₂)₃ samples is reported as a function of temperature and related back to the underlying structural chemistry of these materials. The static solid state proton NMR spectra were also used to identify the proton environment and proton dynamics. These materials represent an improvement upon previous anhydrous proton-conducting materials and represent an important step in finding intermediate temperature proton conductors.     

Electrocatalytic synthesis of ammonia from steam and nitrogen at atmospheric pressure

The electrocatalytic synthesis of ammonia from steam and nitrogen was studied in oxygen ion (O^2?) and proton (H⁺) conducting solid electrolyte cells at 450–700 °C and at atmospheric total pressure. A Ru-based industrial catalyst was used as the working electrode. In the H⁺ cell, steam was electrolyzed at the anode to produce protons and oxygen. Protons, transported to the cathode, reacted with nitrogen to produce ammonia. In the O^2? cell, H₂O and N₂ were fed in together at the cathode. Steam was electrolyzed and the produced hydrogen reacted with nitrogen. Ammonia formation was observed at temperatures between 500 and 700 °C. The conversions with respect to nitrogen or steam were low, primarily because of the poor conductivity of the working electrode. Both cells, however, exhibit promising features that make this alternative approach of ΝΗ₃ synthesis worthy of further investigation.     

Electrical transport properties of doubly Gd- and Al-doped LaGa0.9Mg0.1O2.95 perovskite compounds

Oxide ion conduction properties of La_1−xGd_xGa_0.8Al_0.1Mg_0.1O_2.95 were discussed in terms of tolerance factor and free volume. The oxide ion conductivities increased with Gd content and attained the maximum at x = 0.10. Enhancement in oxide ion conduction up to x = 0.10 was attributable to the approach to an optimum tolerance factor, which is reportedly around 0.96, whereas degradation above x = 0.10 was considered to result from the reduction of free volume caused by replacement of smaller Gd for La.     

Evaluation of ionic conductivity for Mg–Al layered double hydroxide intercalated with inorganic anions

This study demonstrates that humidity, temperature, and the interlayer anions influence ionic conductivities of Mg–Al layered double hydroxides (LDHs) intercalated with inorganic anions. Results show that Mg–Al LDH intercalated with Br^? exhibited the highest ionic conductivity among Mg–Al LDHs intercalated with CO₃^2?, Cl^?, Br^?, NO₃^? and SO₄^2?. Its ionic conductivity was 1.1 × 10^? 2 S cm^? 1 at 80 °C under 80% relative humidity. The electromotive force for the hydroxide ion concentration cell using Mg?Al CO₃^2? LDH showed the same behavior with that using an anion exchange membrane, indicating that Mg–Al CO₃^2? LDH can be a hydroxide ion conductor.     

Vitrification and transport properties in AgBr-doped chalcogenide systems

Vitrification and transport properties measurements for (AgBr)_x(As₂Se₃)_1−x glasses have been carried out in order to investigate the ion conduction phenomena of these systems. Glass samples were successfully obtained in a composition range of 0 ≤ x ≤ 0.65. The addition of AgBr leads these systems to an exponential increase of electrical conductivity. The ionic component of the electrical conductivity is dominant in highly AgBr-doped glasses. The vitrification brings the fast ion conduction to the present glass systems.     

Structural stability of anhydrous proton conducting SrZr0.9Er0.1O3−δ perovskite ceramic vs. protonation/deprotonation cycling: Neutron diffraction and Raman studies

Long-term chemical and structural stability of an ion conducting ceramic is one of the main criteria for its selection as an electrolytic membrane in energy plant devices. Consequently, medium density SrZr_0.9Er_0.1O_3-δ (SZE) anhydrous proton conducting ceramic – a potential electrolyte of SOFC/PCFC, was analysed by neutron diffraction between room temperature and 900 °C. After the first heating/cooling cycle, the ceramic pieces were exposed to water vapour pressure in an autoclave (500 °C, 40 bar, 7 days) in order to incorporate protonic species; the protonated compound was then again analysed by neutron diffraction. This procedure was repeated two times. At each step, the sample was also controlled by TGA and Raman spectroscopy. These studies allow the first comprehensive comparison of structural and chemical stability during the protonation/deprotonation cycling. The results reveal good structural stability, although an irreversible small contraction of the unit-cell volume and local structure modifications near Zr/ErO₅[] octahedra are detected after the first protonation. After the second protonation easy ceramic crumbling under a stress is observed because of the presence of secondary phases (SrCO₃, Sr(OH)₂) well detected by Raman scattering and TGA. The role of crystallographic purity, substituting element and residual porosity in the proton conducting perovskite electrolyte stability is discussed.     

Study on ionic conductivity of polymer electrolyte plasticized with PEG–aluminate ester for rechargeable lithium ion battery

We have synthesized poly(ethylene glycol) (PEG)-aluminate ester as a plasticizer for solid polymer electrolytes. The thermal stability, ionic conductivity and electrochemical stability of the polymer electrolyte which consist of poly(ethylene oxide) (PEO)-based copolymer, PEG–aluminate ester and lithium bis-trifluoromethanesulfonimide (LiTFSI) were investigated. Addition of PEG–aluminate ester increased the ionic conductivity of the polymer electrolyte, showing greater than 10^− 4 S cm^− 1 at 30 °C. The polymer electrolyte containing PEG–aluminate ester retained thermal stability of the non-additive polymer electrolyte and exhibited electrochemical stability up to 4.5 V vs. Li⁺/Li at 30 °C.     

Structural,dielectric and impedance properties of NaCa2V5O15 ceramics

Polycrystalline sample of NaCa₂V₅O₁₅ (NCV) with tungsten bronze structure was prepared by a mixed oxide method at relatively low temperature (i.e. 630 °C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Microstructural study showed that the grains are uniformly and densely distributed over the surface of the sample. Detailed studies of dielectric properties showed that the compound has dielectric anomaly above the room temperature (i.e. 289 °C), and shows hysteresis in polarization study. The electrical parameters of the compound were studied using complex impedance spectroscopy technique in a wide temperature (23–500 °C) and frequency (10²–10⁶ Hz) ranges. The impedance plots showed only bulk (grain) contributions, and there is a non-Debye type of dielectric dispersion. Complex modulus spectrum confirms the grain contribution only in the compound as observed in the impedance spectrum. The activation energy, calculated from the ac conductivity of the compound, was found to be 0.20–0.30 eV. These values of activation energy suggest that the conduction process is of mixed type (i.e. ionic–polaronic).     

The impedance of thin dense oxide cathodes

The impedance is derived for a dense layer electrode of a mixed conducting oxide, assuming that the electronic resistance may be ignored. The influence of layer thickness, oxygen diffusion and surface exchange rate on the ‘General Finite Length Diffusion’ expression is evaluated. The thickness dependence is tested for a series of thin, dense layer electrodes of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) deposited on a Ce_0.9Gd_0.1O_1.95 electrolyte by pulsed laser deposition (PLD). A minimum thickness is required to avoid the influence of contact points of the contacting Pt-gauze and sheet resistance, which is about 1 μm for the studied LSCF electrodes. LEISS surface analysis indicates that PLD deposition process easily leads to a significant Cr contamination of the LSCF surface. Electrochemical impedance spectroscopy analysis indicates that the influence on the exchange rate of this Cr-contamination is still negligible.     

Impedance spectroscopic studies of an organic semiconductor device incorporating a thin film of highly doped ZnPc with MoO3

We use experimental results of low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor, zinc phthalocyanine (ZnPc). The first 10 nm, of a total of 150 nm thermally deposited ZnPc, was doped with molybdenum oxide (MoO₃) by co-evaporation to obtain a 20% doping concentration. The ac electrical parameters were measured at room temperature in the dc bias and frequency ranges of 0–5 V and 100 Hz–0.1 MHz, respectively. The variation of bulk resistance with applied bias presents a clear indication of space charge limited conduction in the fabricated device. The experimental results show a strong frequency dependence of capacitance and loss tangent at low frequencies and high applied bias, while at higher frequencies and low applied bias a weak dependence is observed. Moreover, the ac conductivity shows a strong dependence on frequency and is found to vary as ω^s with the index s≤1.15 suggesting a dominant hopping mechanism of conduction.     

Advanced ion beam technology for versatile oxide thin film formation

Various oxide films, such as SnO₂, In₂O₃, Al₂O₃, SiO₂, ZnO, and Sn-doped In₂O₃ (ITO) have been deposited on glass and polymer substrates by advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry, crystallinity, and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. IBSD method has been carried out for understanding the growth mode of the films on glass and polymer substrate. Relationships between microstructure and electrical properties in ITO films on polymer and glass substrates were intensively investigated by changing ion energy, reactive gas environment, substrate temperature, etc. Smooth-surface ITO films (R_rms ⩽ 1 nm and R_p−v ⩽ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. In the case of Al₂O₃ and SiO₂ films, the oxygen and moisture barrier properties were also improved by IAR surface treatment. The experimental results of the oxide films prepared by the ion beam technologies and its applications will be represented in detail.