Search

International audience

International audience; PrSrCo1-xCuxO4+δ (x = 0.0, 0.1, 0.3, 0.5) are synthesized by solid-state reaction method. The effects of Cu2+ doping on electrical conductivity, thermal expansion, oxygen diffusion properties and oxygen reduction reaction (ORR) activity are investigated. PrSrCo1-xCuxO4+δ oxides crystallize in a single-phase tetragonal structure with I4/mmm space group. Partial substitution Co3+ by Cu2+ results the increase of electrical conductivity and decrease of thermal expansion coefficient. Introducing Cu2+ promotes the formation of interstitial oxygen, accelerates the kinetics of oxygen transport, and significantly improves the electrocatalytic activity of ORR. The lowest area specific resistance (ASR) value of 0.08 Ω cm2 is obtained for the PrSrCo0.7Cu0.3O4+δ cathode at 700 °C in air. The ORR mechanism study demonstrates that Cu-doping (30%) promotes the charge transfer process. The reaction rate control step on PrSrCo0.7Cu0.3O4+δ cathode is the dissociation and surface diffusion process of adsorbed molecular oxygen.

International audience; We report a combined study of whole-rock major- and trace-element geochemistry, SmNd isotope composition, zircon U/Pb dating, and LuHf systematics of peralkaline and aluminous A-type granites from the Ririwai Ring Complex in north-central Nigeria. The Ririwai peralkaline and aluminous A-type granites are strongly ferroan, alkalic to alkali-calcic, and enriched in Hf, Zr, Ga, Rb, Y and REEs. They were emplaced between 176 ± 2.3 Ma and 169.6 ± 0.75 Ma. The peralkaline granites yield relatively higher ɛNd(t) (−2.3 to −1.2) and zircon ɛHf(t) values (−5.8 to −1.7) than the aluminous granites (ɛNd(t) = −3.6 to −3.3; zircon ɛHf(t) = −7.8 to −2.4). In addition, inherited zircons in the aluminous granites yield Pan-African (~590 Ma) ages and low ɛHf(t) values (−14.0). Taken together, these data suggest that the granites formed from extensive fractional crystallization of a transitional basaltic melt derived from an enriched OIB mantle source. The depletions of MgO, CaO, Ti2O, Sr and Ba in the granites indicate that Mg-rich olivine, calcic pyroxene, calcic amphibole, feldspars and FeTi oxides were the major fractionated phases during magma evolution. In addition, several types of evidence, e.g., moderately negative ɛNd(t) and ɛHf(t) values, and the presence of inherited zircons, imply that the parental melt was modified by assimilation of Pan-African upper crust into which the granites were emplaced. A transtensional regime generated prior to late Jurassic breakup of Gondwana, which led to reactivation of shear zones and opening of associated transcurrent faults, paved the way for emplacement of the A-type suite. The Sn–Nb–Zn mineralization of the Ririwai A-type suite was probably linked to complex magmatic evolutionary processes involving extensive fractional crystallization coupled with crustal assimilation and late-stage hydrothermal fluid activity.

Sr-doped double perovskite oxides PrBa 1− x Sr x Co 2 O 5+ δ ( x = 0.0–1.0) are prepared and characterized by X-ray diffraction, X-ray photoelectron spectra, cyclic voltammetry and linear sweep voltammetry, respectively. Sr 2+ doping is found to promote the electrocatalytic activity towards both oxygen evolution reduction and oxygen reduction reaction, due to the concentration enhancement of Co 4+ (e g = 1) on the oxide surface. The PrBa 0.25 Sr 0.75 Co 2 O 5.95 catalyst, with the highest concentration of Co 4+ , exhibits the superior electrocatalytic activity. The onset potential, Tafel slope and the overpotential at given current density of 10.0 mA·cm geom −2 for the OER are 1.52 V, 75.8 mV·dec −1 and 0.42 V, respectively, comparable to the currently reported high performance OER catalysts. At the same time, the onset potential, Tafel slope, limiting current density and electron transfer number of PrBa 0.25 Sr 0.75 Co 2 O 5.95 for ORR are 0.753 V, 58.3 mV·dec −1 , 4.081 mA·cm geom −2 and n = 3.92, respectively, implying much improved ORR activity.

International audience; The double perovskite oxides La2-xNiMnO6-δ (x = 0.0, 0.1, 0.2, 0.3) are evaluated as potential cathodes for intermediate temperature solid oxide fuel cells. The effects of La-deficiency on the crystal structure, high temperature thermal and electrical properties, and catalytic activity for oxygen reduction reaction are comprehensively investigated. La2-xNiMnO6-δ crystallizes in monoclinic structure with the space group P21/n. The cell volume expands with the increase of La-deficiency. The highest electrical conductivity of 25 S cm−1 is found for La1.8NiMnO5.71 at 800 °C in air. Introducing La3+ deficiency greatly improves the amount of chemical adsorbed oxygen species on material surface, which promotes the oxygen reduction reaction of La2-xNiMnO6-δ cathode. The optimum composition, La1.8NiMnO5.71 exhibits the lowest area specific resistance of 0.21 Ω cm2 at 700 °C in air. Meanwhile the peak power density of the anode-supported single cell with La1.8NiMnO5.71 cathode reaches 0.6 W cm−2 at 700 °C. The electrochemical impedance spectra measurements combining with distribution of relaxation times analysis prove that the charge transfer process is the rate-limiting step of the ORR reaction.

We consider a simple hierarchical renormalization model which was introduced in the study of depinning transition in presence of strong disorder, by Derrida and Retaux. Our interest is focused on the critical regime, for which we study the extinction probability, the first moment and the moment generating function. Several stronger assertions are stated as conjectures.

International audience; Anode-supported solid oxide fuel cells consisting of nickel-gadolinium doped ceria (NiO-CGO, 60:40 wt%) anode, gadolinium doped ceria (CGO) electrolyte and lanthanum strontium cobaltite ferrite-gadolinium doped ceria (LSCF-CGO) cathode are developed and operated under single-chamber conditions, utilizing methane/air mixture. The cell performance is optimized regarding the electrolyte microstructure, cathode composition and testing conditions. The performance of the cell improves with the decrease of the thickness of the electrolyte and the increase of the ratio of methane to oxygen. The test cell with LSCF-CGO cathode (70:30 wt%) that was sintered at 1100 °C for 2 h and 150 μm dense electrolyte exhibits the maximum power output of ∼260 mW cm−2 at 600 °C in CH4/O2 = 2 atmosphere.

A cobalt-free perovskite oxide Bi 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3− δ (BSFC) has been investigated as novel cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The BSFC cathode exhibits good thermal stability and chemical compatibility with Ce 0.9 Gd 0.1 O 1.95 (CGO) electrolyte below 950 °C. The average thermal expansion coefficient (TEC) of BSFC is 13.1 × 10 −6 K −1 within a temperature range of 50–800 °C in air, which is close to that of CGO electrolyte. Meanwhile, the polarization resistant values ( R P ) of BSFC cathode on CGO electrolyte are 0.13, 0.32 and 0.76 Ω cm 2 at 700, 650 and 600 °C, respectively; the lowest cathode overpotential is 37 mV at a current density of 125 mA cm −2 at 700 °C in air. The CGO electrolyte-supported single cell with BSFC cathode exhibits maximum power density of 290 mW cm −2 at 700 °C using dry H 2 as the fuel. The rate-limiting step for oxygen reduction reaction (ORR) on BSFC cathode is oxygen surface adsorption-dissociation process. The attractive electrochemical performance demonstrates that BSFC oxide is a promising cathode material for IT-SOFCs.

International audience; The electrochemical performance of Pr2NiMnO6 (PNMO)-xCe0.9Gd0.1O1.95 (CGO) (x = 0–40 wt%) composite oxides as intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode materials are evaluated. The electrochemical impedance spectroscopy (EIS) analysis results identify two consecutive electrode processes on the composite cathode. Among the various composites, PNMO-30CGO cathode exhibits the best electrochemical performance with the minimum polarization resistance of 0.23 Ω cm2 and the maximum exchange current density of 75 mA cm−2 at 700 °C in air. These values are almost constant even after 30-h operation. The oxygen reduction reaction (ORR) mechanism studies prove that the major rate-determining step is the charge-transfer process. Introducing CGO significantly improves the charge-transfer process, by increasing the triple phase boundary (TPB) length and oxygen vacancy concentration in the composite cathode.

International audience; Nd1−xBaCo2O6−δ (N1−xBCO) is evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of Nd-deficiency on the crystal structure, thermal expansion behavior, electrical conductivity and electrochemical performance are studied. N1−xBCO oxides crystallize in the orthorhombic symmetry with Pmmm space group. A good chemical compatibility between N1−xBCO and CGO electrolyte is found at 1100 °C in air. Introducing Nd-deficiency promotes the formation of oxygen vacancy, and significantly improves the electrochemical performance of N1−xBCO cathodes. The lowest area specific resistance (ASR) value of 0.043 Ω cm2 is obtained on the N0.96BCO cathode at 700 °C in air. The rate limiting step for electrochemical oxygen reduction reaction (ORR) is charge transfer process at the interface. The power output of the electrolyte supported cell Ni-CGO/CGO/N0.96BCO reaches 0.6 W cm−2 at 700 °C.

International audience; Sr2−xLaxMnO4+δ (x = 0.4, 0.5, 0.6) oxides were studied as the cathode material for solid oxide fuel cells (SOFC). The reactivity tests indicated that no reaction occurred between Sr2−xLaxMnO4+δ and CGO at annealing temperature of 1000 ◦C, and the electrode formed good contact with the electrolyte after being sintered at 1000 ◦C for 4 h. The total electrical conductivity, which has strong effect on the electrode properties, was determined in a temperature range from 100 to 800 ◦C. The maximum value of 5.7 S cm−1 was found for the x = 0.6 phase at 800 ◦Cin air. The cathode polarization and AC impedance results showed that Sr1.4La0.6MnO4+δ exhibited the lowest cathode overpotential. The area specific resistance (ASR) was 0.39_cm2 at 800 ◦C in air. The charge transfer process is the rate-limiting step for oxygen reduction reaction on Sr1.4La0.6MnO4+δ electrode.

International audience; The development of highly active, inexpensive and clean catalysts for applications in the oxygen evolution reaction (OER) is very important for energy storage and conversion. In this study, a reduced graphene oxide–Co3O4 yolk-shell nanocage (rGO–Co3O4 YSNC) composite material is prepared through a facile precipitation reaction with subsequent calcination and hydrothermal treatment. A strong chemical interaction formed between Co3O4 YSNCs and r-GO nanosheets is vital to produce a well wrapped composite material. This specific composite structure combines the high conductivity of r-GO together with the promising catalytic properties of the highly porous Co3O4 YSNCs, therefore the enhanced OER activity and stability is realized. The Tafel slope, current density at an overpotential of 450 mV and the overpotential at 10.0 mA cm−2 for the rGO–Co3O4 YSNC composite electrode are 84.9 mV dec−1, 19.9 mA cm−2 and 410 mV, respectively. Moreover, the composite electrode exhibits 2.8% attenuation of the current density after the 500th cyclic voltammetry test. These results are comparable to the currently reported high-performance OER catalysts, which prove that the rGO–Co3O4 YSNC composite material is a potential catalyst for oxygen evolution reactions.

International audience; The Pr2CuO4 (PCO) submicrofiber precursors are prepared by electrospinning technique and the thermo-decomposition procedures are characterized by thermal gravity (TG), X-ray diffraction (XRD), Fourier transform infrared spectoscopy (FT-IR), and scanning electron microscopy (SEM), respectively. The fibrous PCO material was formed by sintering the precursors at 900 °C for 5 hrs. The highly porous PCO submicrofiber cathode forms good contact with the Ce0.9Gd0.1O1.95 (CGO) electrolyte after heat-treated at 900 °C for 2 hrs. The performance of PCO submicrofiber cathode is comparably studied with the powder counterpart at various temperatures. The porous microstructure of the submicrofiber cathode effectively increases the three-phase boundary (TPB), which promotes the surface oxygen diffusion and/or adsorption process on the cathode. The PCO submicrofiber cathode exhibits an area specific resistance (ASR) of 0.38 Ω cm2 at 700 °C in air, which is 30% less than the PCO powder cathode. The charge transfer process is the rate limiting step of the oxygen reduction reaction (ORR) on the submicrofiber cathode. The maximum power densities of the electrolyte-support single cell PCO|CGO|NiO-CGO reach 149 and 74.5 mW cm−2 at 800 and 700 °C, respectively. The preliminary results indicate that the PCO submicrofiber can be considered as potential cathode for intermediate temperature solid fuel cells (IT-SOFCs).

International audience; Sr1.5La0.5Mn1-xCoxO4 (SLMCOx) cathode materials for IT-SOFCs (intermediate temperature solid oxide fuel cells) were synthesized by EDTA-citric acid method and characterized by XRD, XPS and EIS, respectively. The results show that SLMCOx has no reaction with Ce0.9Gd0.1O1.95 at 1 200℃ for 12 h. Both the amount of Mn3+ and Co2+ in the oxide increase with the Co doping concentration; at the same time the content of lattice oxygen reduces, and the distortion ratio (c/a) of the lattice increases. The EIS results show that Co-doping dramatically reduces the polarization resistance (Rp) of SLMCOx cathode. The Sr1.5La0.5Mn0.7Co0.3O4 has the lowest Rp of 0.62 Ω·cm2 at 700℃ in air, which is clearly smaller than the Rp value of Sr1.5La0.5Mn0.7O4 that measured at 750℃ (1.5 Ω·cm2). Our results indicate that the Co doped Sr1.5La0.5Mn1-xCoxO4 is potential cathode material for IT-SOFC.

International audience; Double perovskite oxide Pr2NiMnO6 is evaluated as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The reactivity test indicates that no reaction occurs between Pr2NiMnO6 and CGO at 1200 °C in air. The thermal expansion coefficients (TEC) of Pr2NiMnO6 are 10.6 × 10−6 K−1 in air and 11.5 × 10−6 K−1 in nitrogen atmosphere within a temperature range of 100–800 °C. The electrochemical properties of Pr2NiMnO6 cathode are characterized by ac impedance and dc polarization methods, respectively. The lowest area specific resistance (ARS) is 0.38 Ω cm2 at 700 °C in air. The dependence of ASR with oxygen partial pressure indicates that the charge transfer process is the rate-limiting step for oxygen reduction reaction on Pr2NiMnO6 cathode.

Loss of E-cadherin marks a defect in epithelial integrity and polarity during tissue injury and fibrosis. Whether loss of E-cadherin plays a causal role in fibrosis is uncertain. α3β1 Integrin has been identified to complex with E-cadherin in cell-cell adhesion, but little is known about the details of their cross talk. Herein, E-cadherin gene ( Cdh1 ) was selectively deleted from proximal tubules of murine kidney by Sglt2Cre . Ablation of E-cadherin up-regulated α3β1 integrin at cell-cell adhesion. E-cadherin–deficient proximal tubular epithelial cell displayed enhanced transforming growth factor-β1–induced α-smooth muscle actin (α-SMA) and vimentin expression, which was suppressed by siRNA silencing of α3 integrin, but not β1 integrin. Up-regulation of transforming growth factor-β1–induced α-SMA was mediated by an α3 integrin-dependent increase in integrin-linked kinase (ILK). Src phosphorylation of β-catenin and consequent p-β-catenin-Y654/p-Smad2 transcriptional complex underlies the transcriptional up-regulation of ILK. Kidney fibrosis after unilateral ureteric obstruction or ischemia reperfusion was increased in proximal tubule E-cadherin–deficient mice in comparison to that of E-cadherin intact control mice. The exacerbation of fibrosis was explained by the α3 integrin-dependent increase of ILK, β-catenin nuclear translocation, and α-SMA/proximal tubular–specific Cre double positive staining in proximal tubular epithelial cell. These studies delineate a nonconventional integrin/ILK signaling by α3 integrin–dependent Src/p-β-catenin-Y654/p-Smad2–mediated up-regulation of ILK through which loss of E-cadherin leads to kidney fibrosis.

In this study, high-quality mesoporous Fe 3 O 4 nanocages (MFONs) have been synthesized by a facile complex-coprecipitation method at 100 °C with addition of triethanolamine and ethylene glycol. The as-prepared Fe 3 O 4 nanocages possess a mesoporous structure and highly uniform dispersion. When used as an anode material for rechargeable lithium-ion batteries, MFONs anode shows high specific capacities and excellent cycling performance at high and low current rates. At a current density of 200 mA g −1 , the discharge specific capacities are 876 mAh g −1 at the 2nd cycle and 830 mAh g −1 at the 100th cycle. Even at the high current density of 1000 mA g −1 , MFONs anode still retains a stable capacity of 573 mAh g −1 after 300 cycles. This superior electrochemical performance is attributed to the unique mesoporous cage-like structure and high specific surface area (133 m 2 g −1 ) of MFONs, which may offer large electrode/electrolyte contact area for the electron conduction and Li + storage. Furthermore, the good mechanical flexibility of the mesoporous nanocages can readily buffer the massive volume expansion/shrinkage associated with the reversible electrode reaction. These results indicate that MFONs can be used as a promising high-performance anode material for lithium-ion batteries.

International audience; A layered perovskite EuBaCo2O5+δ (EBCO) has been prepared by a solid-state reaction, and evaluated as potential cathode for intermediate-temperature solid oxide fuel cells. Structural characterizations are determined at room temperature using powder X-ray diffraction and transmission electron microscopy technique. The good fits to the XRD data by Rietveld refinement method are obtained in the orthorhombic space group (Pmmm). The lower average thermal expansion coefficient, 14.9 × 10–6 °C–1 between 100 and 800 °C, indicates its better thermal expansion compatibility with conventional electrolytes, compared with the other cobalt-containing cathode materials. The high electrical conductivity and large oxygen nonstoichiometry at intermediate temperatures suggest the effective charge transfer reactions including electron conduction and oxide-ion motion in cathode. As a result, a highly electrochemical activity towards the oxygen reduction reaction is achieved between 600 and 700 °C, as evidenced by low area-specific resistances, e.g. 0.14–0.5 Ω cm2. In addition, cathodic overpotential and oxygen reduction kinetics of the EBCO cathode have also been studied.

International audience; The layered perovskite PrBaxCo2O5+δ (PBxCO, x = 0.90–1.0) oxides have been synthesized by a solid-state reaction technique, and evaluated as the potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature X-ray diffraction patterns show the orthorhombic structures which double the lattice parameters from the perovskite cell parameter as a ≈ ap, b ≈ ap and c ≈ 2ap (ap is the cell parameter of the primitive perovskite) in the Pmmm space group. There is a good chemical compatibility between the PBxCO cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 °C. The electrical conductivity and thermal expansion coefficient of PBxCO are improved due to the increased amount of electronic holes originated from the Ba-deficiency. The results demonstrate the high electrochemical performance of PBxCO cathodes, as evidenced by the super low polarization resistances (Rp) over the intermediate temperature range. The lowest Rp value, 0.042 Ω cm2, and the cathodic overpotential, −15 mV at a current density of −25 mA cm−2, are obtained in the PrBa0.94Co2O5+δ cathode at 600 °C in air, which thus allow to be used as a highly promising cathode for IT-SOFCs. A CGO electrolyte fuel cell with the PrBa0.94Co2O5+δ cathode presents the attractive peak power density of ∼1.0 W cm−2 at 700 °C. Furthermore, the oxygen reduction kinetics of the PrBa0.94Co2O5+δ cathode is also studied, and the rate-limiting steps for oxygen reduction reaction are determined at different temperatures.

International audience; La1.6Sr0.4NiO4 (LSN) nanofibers are prepared by electrospinning technique and used as cathode materials for solid oxide fuel cells (SOFCs) with Ce0.9Gd0.1O1.95 (CGO) as electrolyte. The as-prepared cathode is highly porous but forms a good contact with the CGO electrolyte after rapid sintering at 900 °C for 15 min in air. The electrode performance of LSN nanofibers is measured at various temperatures and under different oxygen partial pressures. Two main oxygen reduction reaction (ORR) processes are identified. The rate limiting step for the ORR is the charge transfer process. The LSN nanofiber cathode exhibits a polarization resistance (Rp) of 0.40 Ω cm2 at 700 °C in air, 0.80 Ω cm2 at 650 °C and 1.59 Ω cm2 at 600 °C. These results demonstrate that the LSN nanofiber architecture significantly enhances the electrochemical activity of these cathodes for the ORR compared to usual porous electrodes, which points out the interest of such a synthesis technique for preparing SOFCs cathode materials with peculiar morphology.

International audience; A-site deficient perovskite La0.57Sr0.15TiO3 (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 Ce0.9Gd0.1O2−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.

International audience; This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa1−xSrxCo2O5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18-0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm−1 at 400-700 °C in air. The results demonstrate the promising performance of YBa1−xSrxCo2O5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21-0.59 Ω cm2 at 700 °C. The lowest ASR, 0.44 Ω cm2, and the cathodic overpotential, −40 mV at a current density of −136 mA cm−2, are obtained in YBaCo2O5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo2O5+δ cathode.

Brownmillerite oxide Ca 2 Fe 1.3 Mn 0.7 O 5+ δ is synthesized and evaluated as a new cathode material for solid oxide fuel cells (SOFCs). The average thermal expansion coefficient (TEC) of Ca 2 Fe 1.3 Mn 0.7 O 5+ δ is 13.3 ± 0.2 × 10 −6 K −1 , close to that of the typical electrolyte materials. The lowest polarization resistance ( R p ) (0.22 ± 0.02 Ω cm 2 at 750 °C in air) and cathodic overpotential values are achieved when the material is sintered at 1000 °C on Ce 0.9 Gd 0.1 O 1.95 (CGO) electrolyte. Two main oxygen reduction reaction (ORR) processes are identified. The rate limiting step for ORR is found to depend on the oxygen partial pressure. The excellent electrochemical performance indicates that Ca 2 Fe 1.3 Mn 0.7 O 5+ δ can be a promising cathode material for SOFCs.

Different amount of metal silver particles are infiltrated into porous Sm 1.8 Ce 0.2 CuO 4 (SCC) scaffold to form SCC–Ag composite cathodes. The chemical stability, microstructure evolution and electrochemical performance of the composite cathode are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance spectroscopy respectively. The composite cathode exhibits enhanced chemical stability. The metal Ag remains un-reacted with SCC and Ce 0.9 Gd 0.1 O 1.95 (CGO) at 800 °C for 72 h. The polarization resistance of the composite cathode decreases with the addition of metal Ag. The optimum cathode SCC-Ag05 exhibits the lowest area specific resistance (ASR, 0.43 Ω cm 2 ) at 700 °C in air. Investigation shows that metal Ag accelerates the charge transfer process in the composite cathode, and the rate limiting step for electrochemical oxygen reduction reaction (ORR) changes to oxygen dissociation and diffusion process.

International audience; K2NiF4-type structure oxides La2Cu1−xCoxO4 (x = 0.1, 0.2, 0.3) are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The materials are characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. The results show that no reaction occurs between La2Cu1−xCoxO4 electrode and Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 °C. The electrode forms good contact with the electrolyte after sintering at 800 °C for 4 h in air. The electrode properties of La2Cu1−xCoxO4 are studied under various temperatures and oxygen partial pressures. The optimum composition of La2Cu0.8Co0.2O4 results in 0.51 Ω cm2 polarization resistance (Rp) at 700 °C in air. The rate limiting step for oxygen reduction reaction (ORR) is the charge transfer process. La2Cu0.8Co0.2O4 cathode exhibits the lowest overpotential of about 50 mV at a current density of 48 mA cm−2 at 700 °C in air.

International audience; A-site non-stoichiometric materials Sr1.5LaxMnO4 (x = 0.35, 0.40, 0.45) are prepared via solid state reaction. The structure of these materials is determined to be tetragonal. Both the lattice volume and the thermal expansion coefficient reduce with the decrease of lanthanum content. On the contrary, the conductivity increases and the maximum value of 13.9 S cm−1 is found for Sr1.5La0.35MnO4 at 750 °C in air. AC impedance spectroscopy and DC polarization measurements are used to study the electrode performance. The optimum composition of Sr1.5La0.35MnO4 results in 0.25 Ω cm2 area specific resistance (ASR) at 750 °C in air. The oxygen partial pressure measurement indicates that the charge transfer process is the rate-limiting step of the electrode reactions.

International audience; Sm1.8Ce0.2CuO4-xCe0.9Gd0.1O1.95 (SCC-xCGO, x = 0-12 vol.%) composite cathodes supported on Ce0.9Gd0.1O1.95 (CGO) electrolyte are studied for applications in IT-SOFCs. Results show that Sm1.8Ce0.2CuO4 material is chemically compatible with Ce0.9Gd0.1O1.95 at 1000 °C. The composite electrode exhibits optimum microstructure and forms good contact with the electrolyte after sintering at 1000 °C for 4 h. The polarization resistance (Rp) reduces to the minimum value of 0.17 Ω cm2 at 750 °C in air for SCC-CGO06 composite cathode. The relationship between Rp and oxygen partial pressure indicates that the reaction rate-limiting step is the surface diffusion of the dissociative adsorbed oxygen on the composite cathode. Highlights : * SCC material exhibits good chemical compatibility with CGO at 1000 °C. * The optimum composite SCC-CGO06 gives the lowest ASR of 0.17 Ω cm2 at 750 °C in air. * The rate-limiting step for oxygen reduction is surface diffusion of the dissociative adsorbed oxygen.

La 1.6 Sr 0.4 NiO 4 –Ag (LSN–Ag) composite cathodes are prepared and characterized by XRD and SEM, respectively. The electrochemical properties of the composite cathodes are investigated using AC impedance and DC polarization methods from 500 to 700 °C under different oxygen partial pressures. The polarization resistance ( R p ) decreases with the increase of Ag content in the composite electrode. The addition of 5 vol.% Ag in LSN results in the lowest R p of 0.21 Ω cm 2 at 700 °C in air. Oxygen partial pressure dependence study indicates that the charge transfer process is the reaction rate limiting step, while the diffusion process has no sensitive to the Ag loading. LSN–5Ag cathode exhibits the lowest overpotential of about 32 mV at a current density of 144 mA cm −2 at 700 °C in air.

International audience; LaBiMn2O6 (LBM) cathode for IT-SOFCs (intermediate temperature solid oxide fuel cells) has been prepared by solid state reaction and studied by XRD and EIS spectrum, respectively. The results show that LBM has no reaction with Ce0.7Bi0.3O1.85(CBO) electrolyte at 1 000 °C for 12 h. AC impedance spectroscopy and DC polarization measurements are used to study the electrode performances+ The polarization resistance decreases with temperature and reaches 0.71 Ω ·cm2 at 700 °C in air. Oxygen partial pressure study indicated that charge transfer process is the major rate limiting step for LaBiMn2O6 cathode from 600 to 700 °C. The LaBiMn2O6 cathode exhibits the lowest overpotential of 85 mV under current density of 216 mA ·cm-2 at 700 °C in air. This preliminary work showes that LaBiMn2O6 material may be potential cathodes for IT-SOFCs.