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Water behavior studies were performed in porous ceramic media based on proton conducting yttrium-doped barium cerate BaCe0.85Y0.15O3-α (BCY15), which is a component of a new high-temperature dual membrane fuel cell (dmFC) design. Complex permittivity measurements were carried out on porous samples at room temperature. A new phenomenon was observed during wetting—a gigantic enhancement of the real component of the capacitance at lower frequencies. A possible explanation is the formation of semi-liquid layer with dipole structure on the pores walls, which is supposed to be organized also at operating temperatures. Since the electrochemically active volumetric layer facilitates the water formation, it should improve the operation of the dmFC by decreasing its resistance, which is experimentally confirmed. This phenomenon can be of importance also for classical proton conducting solid oxide fuel cells, as well as for operation in electrolyzer mode.

International audience; This paper reports impedance studies of a dual membrane fuel cell - an innovative design based on the idea for a junction between an oxygen ion conducting cathode/electrolyte part and proton conducting anode/electrolyte part through a mixed oxygen ion and proton conducting porous membrane. Thus oxygen, hydrogen and water are located in three independent chambers. This concept allows avoiding all the severe pitfalls connected to the presence of water at electrodes in both SOFC and PCFC. The performed measurements of the 3 compartments and the data analysis are improved by introducing some specialized approaches and techniques, which are discussed. The impedance contribution in the proof of the new concept is also presented.

This work presents results of a measurement setup which was constructed for understanding the performance contributions of the individual compartments and reactions taking place in the patented concept of IDEAL-Cell (described in detail in[1]). By inserting a third measurement point at the central membrane of an ideal cell it was possible to measure the cell in three different modes corresponding to hydrogen, oxygen compartment and the full cell. Recorded maximum power densities of (~4, ~7, 11, 16) mW/cm² at (600, 650, 700, 750) °C in H2-O2 atmosphere respectively were observed which were similar to the values of proof of concept ideal cell samples tested so far. Moreover in our setup it was possible to record higher maximum power densities for the hydrogen (proton conducting) compartment which was (~14, 22, 33*, ~38*) mW/cm² at (600, 650, 700, 750) °C.

This paper reports impedance studies of the cathode/electrolyte behaviour in solid oxide fuel cells (SOFC), based on comparative investigation of half-cells with yttria stabilized zirconia (YSZ) electrolyte and different cathode materials: lanthanum strontium manganite (LSM), and composite LSM/YSZ with low ionic conductivity as well as the electron conducting Ag, Pt and Au. For improved impedance data analysis the technique of the differential impedance analysis is applied. It ensures structural and parametric identification without preliminary assumptions about the working model. It is found that despite the low ionic conductivity of LSM, the cathode reaction of the oxide cathode materials is a two-step process including: (i) charge transfer with activation energy of the resistivity E a increasing with the temperature and (ii) transport of oxygen ions through the bulk of the electrode (rate-limiting stage) with E a independent on the temperature. For the metal (electron conducting) electrodes, the reaction behaviour is described with one step process with higher E a at higher temperatures. The activation energy of the electrolyte conductivity decreases with the increase of the temperature. The observed changes in E a for the electrolyte and the cathode reaction (the charge transfer step for the LSM-based electrodes) appear in the same temperature interval. This interesting coincidence suggests for correlation between the bulk (electrolyte) and surface conduction properties. Approaches for improvement of both the ionic conductivity and the supply with electrons in LSM should be also searched.

In this study the technique of the Differential Impedance Analysis (DIA) is applied for distinction of two models which give similar impedance diagrams presented with slightly depressed semi-circles—two time-constants Voigt model with high degree of mixing and one time-constant model in which the capacitance is replaced with constant phase element (CPE). Those two models are often used for impedance investigations of solid state. The applicability of the recognition procedure is confirmed on synthetic models as well as on real samples of yttria-stabilized zirconia (YSZ) and Er-doped BaTiO 3 .

This work shows the enhanced capability of differential impedance analysis (DIA) for recognition of CPE behavior. It is based on the procedure of a secondary DIA, which analyses the frequency dependence of the local operating model parameters' estimates in the zones where there is no adequacy between the object and the local estimator. The new algorithm is successfully examined on synthetic models of CPE, Warburg, Randles, Randles with CPE modification, simple Faradaic reaction with CPE capacitance, as well as on real data obtained on yttrium iron garnet single crystals and yttria stabilized zirconia single crystals.

International audience; Recently a new design of solid oxide fuel cell (SOFC) named dual membrane fuel cell (dmFC) has been introduced and proved. It is based on the introduction of three independent compartments for hydrogen, oxygen and water, which eliminate the dilution of the fuel or the oxidizer respectively in the SOFC construction or in its proton conducting (pSOFC) modification. Due to the registered sufficient mixed ionic conductivity of BaCe0.85Y0.15O2.925 (BCY15), a simplified modification in respect to shaping technology and construction is introduced. It's performance is better than the one of pSOFC cell produced with the same material and shaping procedure: 76 mW/cm2 (dmFC thickness 1.1 mm) against 71 mW/cm2 (pSOFC thickness 0.66 mm) at 700 °C. Impedance measurements carried out down to 1 mHz ensure information about the water formation and behaviour in the separate central membrane compartment of the dmFC design, which brings to performance improvements, registered also in electrolyser mode of operation.

The purpose of this study is to compare the investigations of amorphous magnetic ribbons combining the usual structural methods with physical impedance spectroscopy (PIS) and X-ray photoelectron spectroscopy (XPS). The samples are commercially available rapidly quenched ribbons for torroidal transformers. Two types of ribbons were thermally treated below the temperature of amorphous–crystalline phase transition. Two binding energies of B 1 s electrons are determined by XPS in one of the as-quenched ribbons, which show impedance time constant spectra without dispersion. The other ribbon, possessing only one value of binding energy of the B 1 s electron (B I state) in a rapidly as-quenched state, undergoes transition to a still amorphous state but acquires high electromagnetic losses and show another value of the binding energy of the B 1 s electron (B II state) after the heat-treatment procedure. This latter type of ribbons show structural impedance spectra containing various time constant values.

The nanosized Co, B, H, particles synthesized by the ‘tea’ and ‘antigravity’ methods using a borohydride reduction process have been subjected to structure and composition studies by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected area diffraction (SAD). The amounts of the elements Co, B, O2, H2 and C as mean volume values, and surface values for the as-prepared particles, as well as after Ar+ etching to a depth of about 15 nm and 30 nm from the initial particle surface, are determined. About 1.5 atoms of cobalt per atom of boron correspond to samples obtained by the ‘antigravity’ method. The binding energy (BE) of 1s electrons of boron atoms has only one value. These particles are angular and are in the typical nanocrystalline state. In the case of samples prepared by the ‘tea’ method, two atoms of cobalt per atom of boron are found. The presence of two kinds of BE (B1 and B11) of 1s electrons of boron atoms in the particles obtained by the ‘tea’ method is observed and almost equal amounts of these two states are established in the spectrum. The particles' shape and structure are typical of the amorphous state. The fact that there is one peak when the ‘antigravity’ method is applied, in contrast to the two peaks with the ‘tea’ method indicates the presence of a metal amorphous state in the latter case.

The effect of tap water contaminants on the kinetics of the hydrogen evolution reaction on a nickel electrode in 1 mol dm(-3) KOH was investigated by galvanostatic polarization and electrochemical impedance spectroscopy techniques. It was found that the tap water contaminants lead to an increase in the overpotential of the hydrogen evolution reaction, especially at low temperatures. The combination of electrochemical techniques, as well as physicochemicals such as SEM and EDAX ones, confirmed that the contaminants are specifically adsorbed and blocked the available electrode surface for the reaction. It was concluded that they do not participate in an electrochemical reaction in the potential region where HER occurs. Besides the short term negative impact on the rate of hydrogen evolution, a 55 h test revealed that the overpotential shows a steady increase over time in presence of tap water contaminants, while in absence of these contaminants the overpotential is constant. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

This paper presents results for the conductivity of BaCe0.85Y0.15O2-δ (BCY15) measured by electrochemical impedance spectroscopy in wet hydrogen and in Air, as well as test results from the application of the material in a new dual membrane fuel cell configuration (“IDEAL Cell”), in which the water is produced and evacuated through a separate chamber. The conductivity of dense BCY15 in wet hydrogen atmosphere at 700 °C is 2.0 10-2 S/cm. The measured values in air are of the same order. Preliminary tests of the material in the new cell design, where the three types of conductivity (protonic, oxide ion and mixed) are used in different cell compartments, are successfully performed.

Most electrochemical objects are intrinsically nonstationary or contain valuable evolving phenomena. This paper presents the essentials of the theory of Nonstationary Impedance Spectroscopy (NIS) including the ideas of nonstationary and instantaneous impedance, the new mathematical background and the main approach to the development of nonstationary impedance models. The practical issues for the application of the new techniques are discussed.

The oxygen reduction (OR) mechanism at the Sr-doped LaMnO3 (LSM) and yttria stabilized zirconia (YSZ) composite cathode for high temperature solid oxide fuel cells is still uncertain, despite of the great deal of work carried out over the last years about this system. In previous works, we tested a half-cell (with a YSZ electrolyte pellet) in a typical three-electrode configuration: It was observed that the portion of the composite cathode volume involved in the reaction depends on the operating temperature. Moreover, we analyzed part of the impedance data by the differential impedance analysis, which does not need a preliminary working hypothesis. The results suggested that significant limitations in the oxygen ion transport occur in the LSM pure material, which are not observed in the composite YSZ/LSM cathode. In this study, we investigate the behavior of the LSM/YSZ system in a Ni/YSZ cermet anode-supported half-cell with yttria stabilized zirconia (8YSZ) electrolyte and a screen printed LSM/YSZ composite cathode. The aim is to individuate and characterize the cathodic contribution from the overall impedance response, varying the partial pressure of the reactant gases, to obtain additional information about the OR mechanism from the p(O2) dependence. By a possible interpretation of the oxygen reaction mechanism, a comparative study of the cathode behavior with previous results is performed.

The impedance study of non-stationary systems is of a great interest to electrochemistry concerning the investigation of real objects in low and infra low frequency ranges. The method described in this paper requires the measurement of a consecutive series of impedance diagrams during the time of the system evolution. The analysis of this four-dimensional data set is based on the hypothesis of a continuum of the state and parameter spaces. This approach allows the estimation of the non-stationary transfer function of the system presented by its instantaneous impedance projections. The method described is applied to simulated data and the validity of the non-stationary estimation is verified.

Structural simulation is a new approach to modeling of more complex electrochemical systems, the impedance of which is hard to present in an explicit analytical form. This method is based on the parameters and structure of the impedance model only and eliminates the solution of the impedance equations. It renders possible the simulation of complex models with variation of both their parameters and structures and provides a complete computerization of the simulation process.

The main problem in parameter estimation of electrochemical systems is related to their significant response in a very large frequency range. Using the classical least-squares method leads to the solution of “ill-conditioned” matrices. To avoid this problem, a model reduction method has been developed for parametrical identification of electrochemical systems in the frequency domain. According to this approach, the system is represented by reduced lumped parameter submodels. Parameter estimation of these submodels is consecutively performed using simple least-squares estimators on the basis of the impedance data reduced for the participation of the previous submodels. For more efficient computer handling of the models, a matrix description of the electrochemical impedances is introduced. A number of simulated models and measured data are identified showing the applicability of this method.