Influence of microstructure and crystalline phases on impedance spectra of sodium conducting glass ceramics produced from glass powder

Crystallization of highly ionic conductive N5 (Na₅YSi₄O₁₂) phase from melted Na_3+3x-1Y_1-xP_ySi_3-yO₉ parent glass provides an attractive pathway for cost-effective manufacturing of Na-ion conducting thin electrolyte substrates. The temperature-dependent crystallization of parent glass results in several crystalline phases in the microstructure (N3 (Na₃YSi₂O₇), N5 and N8 (Na8.1Y Si6O18) phases) as well as in rest glass phase with temperature dependent viscosity. The electrical properties of dense parent glass and of compositions densified and crystallized at 700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C are investigated by impedance spectroscopy and linked to their microstructure and crystalline phase content determined by Rietveld refinement. The parent glass has high isolation resistance and predominantly electrons as charge carriers. For sintering at ≥ 900 °C, sufficient N5 phase content is formed to exceed the percolation limit and form ion-conducting pathways. At the same time, the highest content of crystalline phase and the lowest grain boundary resistance are observed. Further increase of the sintering temperature leads to a decrease of the grain resistance and an increase of grain boundary resistance. The grain boundary resistance increases remarkably for samples sintered at 1100 °C due to softening of the residual glass phase and wetting of the grain boundaries. The conductivity of fully crystallized N5 phase (grain conductivity) is calculated from thorough impedance spectra analysis using its volume content estimated from Rietveld analysis, density measurements and assuming reasonable tortuosity to 2.8 10⁻³ S cm⁻¹ at room temperature. The excellent conductivity and easy processing demonstrate the great potential for the use of this phase in the preparation of solid-state sodium electrolytes.

     

Anhydrous Silicophosphoric Acid Glass: Thermal Properties and Proton Conductivity

Anhydrous silicophosphoric acid glass with an approximate composition of H₅Si₂P₉O₂₉ was synthesized and its thermal and proton-conducting properties were characterized. Despite exhibiting a glass transition at 192 °C, the supercooled liquid could be handled as a solid up to 280 °C owing to its high viscosity. The glass and its melt exhibited proton conduction with a proton transport number of ∼1. Although covalent O−H bonds were weakened by relatively strong hydrogen bonding, the proton conductivity (4×10⁻⁴ S cm⁻¹ at 276 °C) was considerably lower than that of phosphoric acid. The high viscosity of the melt was due to the tight cross-linking of phosphate ion chains by six-fold-coordinated Si atoms. The low proton conductivity was attributed to the trapping of positively charged proton carriers around anionic SiO₆ units (expressed as (SiO_6/2)²⁻) to compensate for the negative charges.     

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.     

Structural effects of Zn+2/Mg+2 ratios on crystallization characteristics and microstructure of fluorophlogopite mica-containing glass-ceramics

We report the effect of Mg⁺² substitution (by Zn⁺²) on crystallization kinetics, microstructure, thermal and mechanical properties of boroaluminosilicate glass. Zn²⁺ was selected for Mg²⁺ on the basis of similar ionic radius in six coordination system (Mg²⁺∼0.72 Å, Zn²⁺∼0.75 Å). The melt-quenched glasses with SiO₂–(1 − x) MgO–Al₂O₃–K₂O–B₂O₃–MgF₂ (BPAS)/x ZnO system, have been investigated to establish the effect of Zn⁺²/Mg⁺² ratios. It is found that the density of BPAS glass without zinc content is 2.52 g/cm³ and increased linearly on substitution of Mg²⁺ by 5–32 mol% ZnO. T_g and T_d of BPAS glass initially increased on adding 5 mol% ZnO and then decreased on further addition. From DSC study, it is found that the crystallization exotherm changes significantly in the temperature range 750–1000 °C, where different crystalline phases are formed, and the activation energy of crystallization (E_C) varies in the range of 254–388 kJ/mol. The crystalline phases formed in opaque BPAS glass-ceramic, derived by controlled heat treatment at 800 and 1050 °C (4 h), are identified as fluorophlogopite [KMg₃(AlSi₃O₁₀)F₂] mica and willemite (Zn₂SiO₄) by XRD technique, and confirmed by FTIR spectroscopy. The change of crystallization phenomena varying Zn⁺²/Mg⁺² ratios correspond to significant microstructural change. A wide range of thermal expansion (CTE) values are obtained for the BPAS glasses and corresponding glass-ceramics. CTE (50–500 °C) of BPAS glass without zinc content is 7.76 × 10⁻⁶/K, and decreased sequentially on increasing Zn⁺²/Mg⁺² ratio. The density of glass-ceramics after heating at 800 and 1050 °C increased linearly with increasing Zn⁺² substitution for Mg⁺². Microhardness of the BPAS glasses is in the range of 4.26–6.15 GPa and found to be increased to 4.58–6.78 GPa after crystallized at 1050 °C.     

Thermal,IR, Raman characteristics,Raman gain coefficient and bandwidths in quaternary glasses

Tellurite glasses with composition 75TeO₂–5WO₃–15Nb₂O₅–5M_xO_y in mol%, where M_xO_y = (Na₂O, Ag₂O, ZnO, MgO, CuO, NiO, TiO₂, MnO₂) have been prepared by using the conventional melt-quenching method. Thermal characteristic of prepared glasses were investigated by using DTA techniques. It was found that the glass with the composition 751TeO₂–5WO₃–15Nb₂O₅–5TiO₂ had high thermal stability (ΔT = 122 °C at heating rate 15 K/min). Raman gain coefficients and bandwidths of prepared glasses for Raman gain media were evaluated. The glass with composition 75TeO₂–5WO₃–15Nb₂O₅–5Na₂O had the maximum value of Raman gain coefficient (g = 4.43 × 10⁻¹² m/W) and it was 24 times as large as silica glass. The highest value of full width half maximum (FWHM ≈ 185 cm⁻¹) was observed in glass system 75TeO₂–5WO₃–15Nb₂O₅–5NiO. Finally, the structure of the glasses was investigated through deconvolution Raman and IR spectra.     

Effects of nano-YAG (Y3Al5O12) crystallization on the structure and photoluminescence properties of Nd3+-doped K2O–SiO2–Y2O3–Al2O3 glasses

Nd³⁺-doped precursor glass in the K₂O–SiO₂–Y₂O₃–Al₂O₃ (KSYA) system was prepared by the melt-quench technique. The transparent Y₃Al₅O₁₂ (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd³⁺ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd³⁺ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.     

Alternative proton-conducting electrolytes and their electrochemical performances

This study was focused on the performances of membrane electrode assemblies (MEAs) consisting of the proton–conducting 90PVA/3PWA/4GPTMS/1P₂O₅/2Gl and 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl hybrid membranes as electrolytes together with a Pt/C electrode for proton exchange membrane fuel cells. The MEAs were fabricated and tested as a function of temperature and humidity, and yielded a current density value of about 350?mA?cm^?2 at 60?°C and 100% relative humidity (RH) for the membrane electrolyte 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl. These values were compared with Nafion? membranes, and the single-cell performances based on proton-conducting organic/inorganic hybrid electrolytes were discussed. The test conditions employed were equivalent for each MEA that had an active area of 5?cm². These hybrid membranes showed a high proton conductivity in the range of 10^?3–10^?2 S cm^?1 at low temperatures, i.e., 60, 80, and 90?°C, and 50%, 75%, and 100% RH.     

Proton conductivity and spectral data of Cs<Subscript>2</Subscript>HPO<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O

The Cs₂HPO₄ · 2H₂O single crystals synthesized from an aqueous solution containing equimolar amounts of H₃PO₄ and Cs₂CO₃ were studied by impedance and IR spectroscopy, X-ray diffraction analysis, and differential scanning calorimetry (DSC). The IR spectra were analyzed in accordance with the structural data, and the absorption bands were assigned. The proton conductivity was studied at temperatures in the range 20–250°C. The conductivity of dehydrated Cs₂HPO₄ was low, ~10^–5–10^–9 S cm^–1 at 90–250°C with an activation energy of conductivity E _a = 1.1 eV at 130–250°C. The processes determining the character of the temperature dependence of conductivity were consistent with the DSC and thermogravimetry data. According to these data, dehydration of the crystalline hydrate Cs₂HPO₄ · 2H₂O starts at 60°C and occurs in three stages, forming Cs₂HPO₄ · 1.5H₂O below 100°C; anhydrous Cs₂HPO₄ at t > 160°C, which is stable up to 300°C; and Cs₄P₂O₇ above 330°C.     

Crystallization of MgFe2O4 from a glass in the system K2O/B2O3/MgO/P2O5/Fe2O3

Spherical magnetic Mg-Fe-O nanoparticles were successfully prepared by the crystallization of glass in the system K₂O/B₂O₃/MgO/P₂O₅/Fe₂O₃. The magnetic glass ceramics were prepared by melting the raw materials using the conventional melt quenching technique followed by a thermal treatment at temperatures in the range 560–700 °C for a time ranging from 2 to 8 h. The studies of the X-ray diffraction, electron microscopy and FTIR spectra confirmed the precipitation of finely dispersed spherical (Mg, Fe) based spinel nanoparticles with a minor quantity of hematite (α-Fe₂O₃) in the glass matrix. The average size of the magnetic nano crystals increases slightly with temperature and time from 9 to 15 nm as determined by the line broadening from the XRD patterns. XRD studies show that annealing the glass samples for long periods of time at temperature ≥604 °C results in an increase of the precipitated hematite concentration, dissolution of the spinel phase and the formation of magnesium di-borate phase (Mg₂B₂O₅). For electron microscopy, the particles were extracted by two methods; (i) replica extraction technique and (ii) dissolution of the glass matrix by diluted acetic acid. An agglomeration of the nano crystals to larger particles (25–35 nm) was observed.     

A supramolecular complex based on poly-Keggin-anion chains: synthesis, structure characterization, and conductivity

Abstract  

A proton-conductive supramolecular complex, {[Cu(H₂O)₈][H(H₂O)₃](HINO)₄(PMo₁₂O₄₀)} _n , was constructed by a self-assembly of H⁺(H₂O)₃ clusters, [Cu(H₂O)₈]²⁺ clusters, [PMo₁₂O₄₀]³⁻ anions, and isonicotinic acid N-oxide (HINO). Single-crystal X-ray diffraction analysis at 293 K revealed that the complex presented the three-dimensional (3D) supramolecular framework built from non-covalent interactions. Interestingly, [PMo₁₂O₄₀]³⁻ anions self-assembled into poly-Keggin-anion chains in the supramolecular framework. Thermogravimetric analysis shows no weight loss in the temperature range of 20–100 °C, indicating that all water molecules in the unit structure are not easily lost below 100 °C. Surprisingly, the proton conductivity of the complex in the temperature range of 85–100 °C under 98% RH condition reached good proton conductivity of 10⁻³ S cm⁻¹. A possible mechanism of the proton conduction was proposed according to the experimental results.     

Electric properties of oxyfluorides Ba2In2O5−0.5x F x with brownmillerite structure

Synthesis of fluoro-substituted substances based on brownmillerite Ba₂In₂O₅ is carried out. The width of the homogeneity region of the Ba₂In₂O_5?0.5x F _x (0 < x ≤ 0.25) solid solution was established using X-ray analysis. Measurement of temperature dependences of conductivity in atmospheres with different partial pressure of water vapor (pH₂O = 3.3 and 2 × 10³ Pa) showed an increase in conductivity at T ≤ 550°C in a humid atmosphere, which is due to appearance of proton transport. The dependence of conductivity on partial oxygen pressure (pO₂ = 0.21 × 10⁵ to 10^?15 Pa) is studied in the temperature range of 500–1000°C; ion transport numbers are calculated. The method of polarization measurements was used to determine transport numbers of fluoride. Total conductivity is divided into ion (proton, oxygen, and fluoride ion) and electron components. Analysis of concentration dependences of conductivities showed that low concentrations of fluoride allow increasing both the total and partial conductivities (oxygen-ion and proton) and, besides, allow shifting the “order-disorder” phase transition by 100°C to the low temperature range.     

The effect of PO<Subscript>2,5</Subscript> and AlO<Subscript>1,5</Subscript> additions on structural changes and crystallization behavior of SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> sol-gel derived glasses and thin films

SiO₂-TiO₂-PO_2,5 (STP) and SiO₂-TiO₂-AlO_1,5 (STA) glasses were prepared by sol-gel processing. Their infrared absorption spectra (IR), differential thermal analysis curves (DTA) and X-ray diffraction patterns (XRD) have been recorded. In the SiO₂-TiO₂ system, the chemical homogeneity of the sol-gel glass could be evaluated by the relative concentration of Si-O-Ti heterocondensation comparing to Si-O-Si homocondensation. For the STA system, a gradual decrease of the Si-O-Ti/Si-O-Si band ratio (based on IR spectra) with the addition of Al₂O₃ is observed, with the simultaneous formation of Si-O-Al and Ti-O-Al bounds, i.e Al₃ ⁺ ions are dissolved in the SiO₂-TiO₂ glass matrix and do not promote glass-in-glass phase-separation in the composition range of 0–15 mol% AlO_1.5. In the STP system, on the other hand, P=O bond IR stretch in the ternary glasses indicates that P=O free PO₂O_2/2 ⁻ tetrahedra are formed, rather than the double bonded POO_3/2 tetrahedra that usually occur in binary SiO₂-P₂O₅ glasses. It can be concluded that SiO₂-TiO₂-P₂O₅ glass separates into a SiO₂-rich phase and a TiO₂(P₂O₅)-rich phase. During heat-treatment in STA system only anatase precipitates, even at T ~ 1,000 °C, while in for STP, anatase (TiO₂) or (TiO)₂P₂O₇ (TOP) crystals precipitate at ~600 °C, depending on the P₂O₅ concentration. The major crystal phase, cristobalite, precipitated at ~1,000 °C and at ~1,200 °C, the P-containing phase melts.     

Microstructure and protonic conductivity of H3PO4‐doped polyethylenimine–siloxane chemically covalently organic–inorganic hybrids

The chemically covalent polyethylenimine–siloxane hybrids doped with various amounts of ortho‐phosphoric acid (H₃PO₄) were prepared and characterized by FTIR, DSC, TGA, and solid‐state NMR spectra. The protonic conduction behavior of these materials was also investigated by means of impedance measurements. These observations indicate that the hydrogen bonding and protonic interactions exist between the dopant H₃PO₄ and the hybrid host, resulting in an increase in T _g of polyethylenimine segments. These hybrids are thermally stable up to 200 °C from TGA analysis. Conductivity studies show an Arrhenius behavior characteristic and the Grotthus‐like proton conduction, and a high conductivity of 10^?2–10^?3 S cm^?1 at 110 °C in dry atmosphere for the hybrid membrane with H₃PO₄/EI of 0.5. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2135–2144, 2006     

Chemically modified proton‐conducting membranes based on sulfonated polyimides: Improved water stability and fuel‐cell performance

A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g^?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm^?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm^?1 at 50% relative humidity. In a single H₂/O₂ fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006     

BaCe0.8Ho0.2O3-a陶瓷的性质与应用

Ceramic BaCe0.8Ho0.2O3-α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600-1000 ℃ in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600-1000 ℃ was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600-900 ℃ in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 ℃. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01-0.09, and the oxide-ionic transport numbers were 0.27-0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 ℃, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 ℃, the maximum short-circuit current density and power output density were 346 mA/cm^2 and 80 mW/cm^2, respectively.     

Structural and Optical Properties of Sol-Gel Deposited Proton Conducting Ta2O5 Films

Proton conducting tantalum oxide films were deposited on ITO (Indium Tin Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prepared using Ta(OC₂H₅)₅ as a precursor. X-ray diffraction studies determined that the sol-gel films, heat treated at temperatures below 400°C, were amorphous. Films heat treated at higher temperatures were crystalline with the hexagonal δ-Ta₂O₅ structure. The solar transmission values (T _s ) of tantala films on glass generally range from 0.8–0.9, depending on thickness. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the UV-VIS-NIR regions. The refractive index values calculated at λ=550 nm increased fromn=1.78 to 1.97 with increasing heat treatment from 150 to 450°C. The films heat treated at different temperatures showed low absorption, with extinction coefficients of smaller thank=1×10⁻³ in the visible range. Impedance spectroscopic investigations performed on Ta₂O₅ films revealed that these films have a protonic conductivity of 3.2×10⁻⁴S/m. The films are suitable for proton conducting layers in electrochromic (EC) devices.     

Preparation via microemulsion method and proton conduction at intermediate-temperature of BaCe1−xYxO3−α

The ceramic powders of BaCe_1?xY_xO_3?α (x = 0.05, 0.10, 0.15, 0.20) have been prepared via a microemulsion method. Green compacts of the powders were sintered to densities higher than 95% of theoretical at the lower temperature (1500 °C). The obtained ceramics showed a single-phase of orthorhombic perovskite. The proton conduction was investigated by employing the techniques of AC impedance and electrochemical hydrogen permeation (hydrogen pumping) at 300–600 °C. It was found that the ceramics were almost pure proton conductors in wet hydrogen, and the highest proton conductivity was observed for x = 0.15 at 600 °C. Ammonia was synthesized successfully from nitrogen and hydrogen at atmospheric pressure in the electrolytic cell using BaCe_0.85Y_0.15O_3?α. The maximum rate of NH₃ formation was found to be 2.1 × 10^?9 mol s^?1 cm^?2 at 500 °C with an applied current of 0.75 mA.     

NaNbO3 crystals dispersed in a B2O3 glass matrix – Structural characteristics versus electrical and dielectrical properties

Sodium niobate (NaNbO₃) is a crystal with a perovskite structure that exhibits, at room temperature, an antiferroelectric behaviour. It is a very interesting material due to the several phase transitions that it presents as a function of the temperature (ferroelectric–antiferroelectric–paraelectric). Thus, the preparation of glass-ceramics containing NaNbO₃ crystals is scientifically and technologically important. Besides, there is actually few works available about the preparation of NaNbO₃ crystals embedded in a glass matrix. The present work reports the preparation process and the study of glass and glass-ceramics in the B₂O₃–NaNbO₃ system.The glass with the molar composition 60B₂O₃–30Na₂O–10Nb₂O₅ (mol%) was prepared by the melt-quenching method. Sodium niobate (NaNbO₃) crystallites were precipitated through a controlled heat-treatment (HT) process. NaNbO₃ crystallites were detected by X-ray diffraction (XRD) in the samples treated above 500 °C. The treatments above 600 °C favour also the formation of Na₂B₄O₇ and Nb₂O₅ crystalline phases.Scanning electron microscopy (SEM) reveals that the crystallization occurs in volume and that the number of particles increases with the rise in HT temperature.The number of network modifier ions (Na⁺ and Nb⁵⁺) in the glass network is the main factor in the dc and ac conductivity behaviours. The dielectric constant (?′) value increases with the increase of the volume ratio between the particles and the glass matrix. The sample heat-treated at 550 °C shows two thermally stimulated depolarization current (TSDC) peaks. The high temperature peak can be related to the presence of NaNbO₃ particles.     

Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid-catalyzed crosslinking for proton exchange membrane fuel cells

Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01–0.19 S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H₂/O₂ fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm² (Pd/C) exhibited a peak power density of 220.3 mW/cm², which was close to that of Nafion 212 (214.0 mW/cm²) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.     

Optimization of the electrochemical performance of a Ni/Ce0.9Gd0.1O2−δ-impregnated La0.57Sr0.15TiO3 anode in hydrogen

A-site deficient perovskite La_0.57Sr_0.15TiO₃ (LSTO) materials are synthesized by a modified polyacrylamide gel route. X-ray diffraction pattern of LSTO indicates an orthorhombic structure. The thermal expansion coefficient of LSTO is 10.0 × 10⁻⁶ K⁻¹ at 600 °C in 5%H₂/Ar. LSTO shows an electrical conductivity of 2 S cm⁻¹ at 600 °C in 3%H₂O/H₂. A new composite material, containing the porous LSTO backbone impregnated with small amounts of Ce_0.9Gd_0.1O_2−δ (CGO) (3.4–8.3 wt.%) and Ni/Cu (2.0–6.3 wt.%), is investigated as an alternative anode for solid oxide fuel cells (SOFCs). Because of the substantial electro-catalytic activity of the fine and well-dispersed Ni particles on the surface of the ceramic framework, the polarization resistance of 6.3%Ni-8.3%CGO-LSTO anode reaches 0.73 Ω cm² at 800 °C in 3%H₂O/H₂. In order to further improve the anodic performance, corn starch and carbon black are used as pore-formers to optimize the microstructure of anodes.