Daria Vladikova

Selectivity study of the differential impedance analysis*/comparison with the complex non-linear least-squares method

The analytical power of the differential impedance analysis (DIA) as a new approach for model identification is investigated. The minimum of the ratio q of the two time-constants T1 and T2 (q=T2/T1) describing a two step reaction with ladder structure, at which the second time-constant T2 is recognized, is accepted as a measure for the selectivity evaluation. The investigation is performed on synthetic models with variation of q in the interval from 30 to 0.001. The influence of data quality is studied by applying data truncation from seven to two digits, as well as by introduction of a wild point. Experimental data measured on two actual dummy cells with q equal to 30 and 0.03, respectively, are also analyzed. The results are compared with those obtained by applying the algorithm of the wide-spread complex non-linear least-squares method, performed on zview software product. The comparative study demonstrates a higher selectivity of the DIA, combined with an additional noise immunity and increased robustness of the analysis.

Application of the differential impedance analysis for investigation of electroceramics

Abstract This work shows the enhanced performance of Impedance Spectroscopy for investigation and characterization of electroceramics by applying a new structural approach for data analysis, called Differential Impedance Analysis (DIA). The main advantage of this technique is the possibility for model identification directly from the experimental data, i.e. without the use of a preliminary working hypothesis. DIA provides for separation and phenomenological characterization of the different steps involved in the investigated object. The capabilities of the method are demonstrated in conductivity studies of yttrium iron garnet (YIG) single crystal and Er doped PTCR BaTiO 3 . The analysis ensures a more detailed investigation of the bulk properties of YIG, including the separation and characterization of the hopping conductivity. The application of DIA on BaTiO 3 enriches the information about the role of the ferroelectric domain structure on the PTCR.

IDEAL-Cell, Innovative Dual mEmbrAne fueL-Cell: Fabrication and Electrochemical Testing of First Prototypes

The IDEAL-Cell concept is based on the junction between a PCFC anode/electrolyte section and a SOFC cathode/electrolyte section, through a mixed proton and oxide ion conducting porous ceramic membrane, operating in the temperature range 600-700°C. Recombination of ions takes place within the junction, or central membrane (CM), and water vapor is evacuated through open porosity. The first results on the fabrication of multilayered samples reproducing the IDEAL-Cell structure are reported here, together with electrochemical tests carried out on selected samples in order to evaluate the performances of the chosen materials and to demonstrate the feasibility of this innovative concept of fuel cell.

Gigantic enhancement of the dielectric permittivity in wet yttrium-doped barium cerate

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.

Towards Understanding the Dual Membrane Fuel Cell (IDEAL-Cell) Using a Metallic Central Membrane

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 this 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.