Electrochemical performance of LaNi0.6Co0.4O3-δ–Ce0.9Gd0.1O1.95 composite electrode and evaluation of its effective reaction length

Journal of Solid State Electrochemistry - The electrochemical properties of LaNi0.6Co0.4O3-δ–Ce0.9Gd0.1O1.95 composite electrodes as a function of temperature and p(O2) were investigated...     

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.     

Electrochemical characteristics of Ce0.8Gd0.2O1.9|La0.6Sr0.4CoO3-δ + Ce0.8Gd0.2O1.9 half-cell

The analysis of the medium temperature half-cell Ce_0.8Gd_0.2O_1.9|70 wt% La_0.6Sr_0.4CoO_3- (LSCO) + 30 wt % Ce_0.8Gd_0.2O_1.9 (CGO) has been made by electrochemical impedance, cyclic voltammetry and chronoamperometry. The shape of complex impedance plots depends on temperature and cathodic polarisation of the electrode. Nyquist (Z, Z-) plots were fitted by equivalent circuit taking into account the electrolyte properties (at very high frequencies), charge transfer process at grain boundaries (at high frequencies), and medium and low frequency O₂ reduction process at the cathode surface and inside the porous cathode material. Two different time constants have been obtained for the cathode process, i.e. for electroreduction of oxygen. It was found that the addition of CGO into the cathode material (LSCO) only somewhat decreases the surface catalytic activity but the noticeably higher low-frequency resistance (i.e. mainly diffusion-like mass transfer resistance R_D) values at lower temperatures have been calculated. It was found that the mainly bulk diffusion-limited process at T773 K deviates toward the kinetically mixed process (diffusion + charge transfer) with increasing temperature.     

Investigation of Pr2NiMnO6‐Ce0.9Gd0.1O1.95 composite cathode for intermediate-temperature solid oxide fuel cells

Journal of Solid State Electrochemistry - The electrochemical performance of Pr2NiMnO6 (PNMO)-xCe0.9Gd0.1O1.95 (CGO) (x = 0–40 wt%) composite oxides as...     

Electrochemical reduction of NO and O2 on La2−x Sr x CuO4-based electrodes

A series of La_2 − x Sr _x CuO₄ (x = 0.0, 0.05, 0.15, 0.25 and 0.35) compounds was investigated for the use of direct electrochemical reduction of NO in an all-solid-state electrochemical cell. The materials were investigated using cyclic voltammetry in 1% NO in Ar and 10% O₂ in Ar. The most selective electrode material was La₂CuO₄, which had an activity of NO reduction that was 6.8 times higher than that of O₂ at 400 °C. With increasing temperature, activity increased while selectivity decreased. Additionally, conductivity measurements were carried out, and the materials show metallic conductivity behavior which follows an adiabatic small polaron hopping mechanism.     

Functional properties and electrochemical performance of dual-phase Pr0.9Y0.1BaCo2O6−δ–Ce0.8Sm0.2O1.9 composite cathodes

Journal of Solid State Electrochemistry - The dual-phase composites are obtained by mixing perovskite-like cobaltite Pr0.9Y0.1BaCo2O6–δ and samarium-doped ceria Ce0.8Sm0.2O1.9 in weight...     

Evaluation of kinetic stability against CO2 and conducting property of BaCe0.9−xZrxY0.1O3−δ

In order to prepare high proton conducting oxide with high chemical stability against CO₂ at 600–800 °C, preparation of BaCe_0.9?xZr_xY_0.1O_3?δ was examined. Almost single-phase could be prepared for the specimens with x = 0.0–0.2 by Pechini method. Reaction kinetics between BaCe_0.9?xZr_xY_0.1O_3?δ and CO₂ could be explained by Jander model. With increasing Zr content up to 0.2, apparent rate constant determined from Jander plot decreased by about one order, showing improvement of kinetic stability against CO₂. It was also clarified that influence of partial Zr substitution on electrical property was slight, leading to the conclusion that BaCe_0.7Zr_0.2Y_0.1O_3?δ exhibited both high kinetic stability against CO₂ and relatively high proton conduction.     

Preparation of aqueous sols of Ce1 − x Gd x O2-δ, Y0.9Eu0.1VO4 and nanocomposites Ce1 − x Gd x O2-δ/Y0.9Eu0.1VO4 stabilized by polyacrylic acid

A method for the synthesis of stable aqueous sols of nanocrystalline solid solutions Ce_1?x Gd _x O_2-δ (x = 0.10, 0.15, 0.20) and Y_0.9Eu_0.1VO₄ and nanocomposites Ce_{1 ? x} Gd _x O_2-δ/Y_0.9Eu_0.1VO₄ stabilized by biocompatible low-molecular-weight polyacrylic acid was proposed. Polyacrylic acid was shown to be a promising matrix for the preparation of polyfunctional composite materials.     

Electrochemical testing of composite electrodes of (La1?x Sr x ) s MnO3 and doped ceria in NO-containing atmosphere

The possibility of using electrochemical cells for removal of NO _x from an exhaust gas with excess O₂ has been examined. (La_1−x Sr _x ) _s MnO₃ (LSM) and ceria doped with Pr or Gd were selected as electrode materials and investigated in three-electrode cells. The electrodes were characterised electrochemically with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the gas composition monitored while the electrodes were polarised. The electrodes of (La_0.5Sr_0.5)_0.99MnO₃ (LSM50) and Ce_0.8Pr_0.2O_2−δ exhibit higher current densities in 0.1% NO in Ar than in air at 300 to 400 °C during CV. This indicates some apparent selectivity towards NO compared to O₂. The electrodes can remove NO, when polarised to at least −0.6 V vs. Pt/Air at 600 °C, and EIS measurements under polarisation indicate that the kinetics of the electrodes change, when the electrode potential gets below −0.6 V vs. Pt/Air.     

Oxygen permeation and stability of Zr0.8Y0.2O0.9‒La0.8Sr0.2CrO3-δ dual-phase composite

A tubular membrane made of Zr_0.8Y_0.2O_1.9 (60 vol%) and was prepared by a standard ceramic process. Oxygen permeation through the membrane tube was examined by exposing its outer shell to air and sweeping its inner wall with pure helium or CO balanced with helium. An oxygen flux of 9.2×10⁻⁹ mol cm⁻² s⁻¹ was measured at 950°C under air/He gradient, and a larger flux of 3.2×10⁻⁸ mol cm⁻² s⁻¹ at 930°C under air/CO gradient. The membrane tube was found to exhibit excellent stability under highly reducing atmosphere and elevated temperatures. The oxygen permeation rate is likely to be increased through the modification of the surface and reduction of the membrane thickness.     

Electrode performance of La2NiO4+δ cathodes in contact with La0.9Sr0.1ScO3−δ proton-conducting oxide

Journal of Solid State Electrochemistry - Ruddlesden-Popper-structured La2NiO4+δ oxide has been applied for the first time as the cathode for La0.9Sr0.1ScO3−δ proton-conducting...     

Kinetics of methane electrooxidation in pure and composite anodes of La0.3Y0.1Sr0.4TiO3−δ

Journal of Solid State Electrochemistry - The electrochemical characteristics of electrolyte-supported solid oxide fuel cells containing pure perovskite anode of La0.3Y0.1Sr0.4TiO3−δ,...     

Thermal stability and features of the synthesis of mixed ceramic oxides La2−x Sr x CoO4

Thermal behavior of the mixed oxides La_2?x Sr _x CoO₄ (0.1 < x < 1.5) in the temperature range 1200–1700 K was studied. The use of the ceramic synthesis method makes it possible to obtain homogeneous samples at the calcination temperature of 1673 K. It was found by the high-temperature mass-spectrometry method that a charge can be depleted of cobalt oxide during the high-temperature synthesis.     

Effect of graphite pore former on oxygen electrodes prepared with La0.6Sr0.4CoO3−δ nanoparticles

This study aimed at fabricating porous crack-free and delamination-free La_0.6Sr_0.4CoO_3?δ electrodes using nanopowders and investigating oxygen reduction (occurring at solid oxide fuel cell cathodes) and oxygen evolution (occurring at solid oxide electrolysis cell anodes) at 600 °C in air. The electrodes were deposited by screen-printing on Ce_0.8Gd_0.2O_1.9 substrates. The pastes were prepared with nanoparticles synthesised by flame spray synthesis and graphite pore former. Without graphite, the electrodes sintered at 1000 °C exhibit relatively low porosity and significant densification which led to partial delamination and large overpotentials. The addition of graphite, which was removed by combustion at ca. 650 °C during sintering, markedly improves electrode performance by increasing porosity and reducing densification. A minimal overpotential for both the oxygen reduction and oxygen evolution was reached for a layer porosity of ca. 50–60 vol.%.     

Surface modification of La0.3Sr0.7CoO3−δ ceramic membranes

The dependence of oxygen permeability of dense La_0.3Sr_0.7CoO_3−δ ceramics on membrane thickness indicates significant surface exchange limitations to the permeation fluxes, which suggests a possibility to increase membrane performance by surface activation. The cobaltite membranes with various porous layers applied onto the permeate-side surface were tested at 850–1120 K. Silver-modified La_0.3Sr_0.7CoO_3−δ membranes showed enhanced permeation at temperatures above 950 K; deposition of porous layers of PrO_x and Pr_0.7Sr_0.3CoO_3−δ had no positive effect. The maximum oxygen permeability at 850–1120 K was observed in the case of porous La_0.3Sr_0.7CoO_3−δ layers with surface density about 10 mg cm⁻². These results suggest that the surface exchange of lanthanum–strontium cobaltite membranes under an oxygen chemical potential gradient is limited by both oxygen sorption at the surface and ion diffusion through the surface oxide layers. Oxygen permeability of La_0.3Sr_0.7CoO_3−δ ceramics was found to increase with increasing grain size due to decreasing grain-boundary resistance to ionic transport.     

Electrochemical evaluation of La2NiO4+δ -based composite electrodes screen-printed on Ce0.8Sm0.2O1.9 electrolyte

La₂NiO_4+δ , 60 wt.% La₂NiO_4+δ –40 wt.% La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ , and 60 wt.% La₂NiO_4+δ –40 wt.% Ce_0.8Sm_0.2O_1.9 electrodes were prepared from fine powders on dense Ce_0.8Sm_0.2O_1.9 electrolyte substrates by screen-printing technique. Electrochemical impedance spectroscopy and chronopotentiometry techniques were employed to evaluate the electrochemical properties of the composite electrodes in comparison with the La₂NiO_4+δ electrode. For the three electrodes, main electrode processes were resolved to be charge-transfer at the electrode/electrolyte interface and oxygen exchange on the electrode surface. The contribution of the surface oxygen exchange process was detected to be dominant for the overall electrode polarization. The addition of Ce_0.8Sm_0.2O_1.9 into La₂NiO_4+δ was favorable for the charge transfer process whereas it was undesired for the surface oxygen exchange process. On comparison, adding La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ into La₂NiO_4+δ was found to benefit both the two electrode processes. The La₂NiO_4+δ -La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ composite electrode showed optimum electrochemical properties among the three electrodes. At 800 °C, the composite electrode achieved a polarization resistance of 0.20 Ω cm², an overpotential of 45 mV at a current density of 200 mA cm^?2, together with an exchange current density of ～200 mA cm^?2.     

Structure,chemical stability and electrical properties of BaCe0.9Y0.1O3−δ modified with V2O5

Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe_0.9Y_0.1O_3?δ–V₂O₅ system. Single-phase BaCe_0.9Y_0.1O_3?δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO₃ in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO₄ and BaV₂O₆) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO₂/H₂O. All BaCe_0.9Y_0.1O₃-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe_0.9Y_0.1O_3?δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe_0.9Y_0.1O_3?δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO₃ lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO₃ during applied synthesis procedure.

     

Electrochemical properties of La0.8Sr0.2FeO3 − δ –La0.45Ce0.55O2 − δ composite cathodes for intermediate temperature SOFC

The electrochemical properties of La_0.8Sr_0.2FeO_3???δ (LSF)–La_0.45Ce_0.55O_2???δ (LDC) composite cathodes coated on LSGM electrolyte were studied by electrochemical impedance spectroscopy and cathodic polarization technique. Results showed that the composite cathodes possessed superior electrochemical performance compared to that of pure LSF cathode. The cathodic overpotential of Cathode C was only 100 mV at 0.3 A cm^?2, and the charge transfer resistance and the gas phase diffusion resistance were decreased to 0.105 Ω cm² and 0.257 Ω cm², respectively at 800 °C. The improvement of the electrochemical performance is contributed to the increase of the triple-phase boundary, enlargement of the effective area for electrode reaction, and increase of the porosity of the cathode by adding LDC to the cathode material.     

Nd0.6-xBaxSr0.4Co0.2Fe0.8O3-δ-30％Ce0.9Gd0.1O1.95复合阴极的性能

采用溶胶-凝胶法合成了Nd0.6-xBaxSr0.4Co0.2Fe0.8O3-δ(NBSCF)阴极粉体和Ce0.9Gd0.1O1.95(GDC)电解质粉体.利用X射线衍射仪(XRD)、电子能谱仪(XPS)分别对NBSCF的结构及其与GDC的化学相容性、NBSCF表面的化学状态进行表征.用直流四端子法和交流阻抗谱法分别测...