Experimental and Modeling Study of the Impedance of Ni/YSZ Cermet Anodes

Gewies, Stefan; Bessler, Wolfgang G.; Sonn, Volker; Ivers‐Tiffée, Ellen

doi:10.1149/1.2729264

Cited by 24 publications

(25 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…50 The introduction of two RQ elements mirrors the shape of the anode spectra simulated by the physical-based model ( Figure 7B), which shows two overlapping arcs. This choice has two consequences: only the sum of the resistances (R an tot = R an1 + R an2 ) can be compared to the anode resistance simulated by the model (R an ); the equivalent capacitances estimated via fitting cannot be directly compared to the double layer capacitances included in the model for the electrode/electrolyte interface.…”

Section: Impedance Experiments At 700mentioning

confidence: 71%

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

Rahmanipour

Pappacena

Boaro

et al. 2017

J. Electrochem. Soc.

View full text Add to dashboard Cite

A distributed charge transfer model for IT-SOFCs with MIEC electrolyte and composite electrodes is developed. A physically-based description of the electronic leakage current in the electrolyte is included, together with mass and charge conservation equations. The model is applied to simulate experimental polarization curves and impedance spectra collected on IT-SOFCs consisting of SDC electrolytes, Cu-Pd-CZ80 infiltrated anodes and LSCF/GDC composite cathodes. Hydrogen electro-oxidation experiments are examined (H 2 /N 2 humidified mixtures, 700 • C, 30-100% H 2 molar fraction). A significant increase of the ohmic resistance measured in the impedance spectra is revealed at decreasing the H 2 partial pressure or increasing the voltage (from 0.71 cm 2 at 100% H 2 to 0.81 cm 2 at 30% H 2 ). Good agreement between the calculated and experimental polarization and EIS curves is achieved by fitting the exchange current density and the capacitance of each electrode. Model and theoretical analyses allow to rationalize the observed shift of the ohmic resistance, highlighting the key-role played by the electronic leakage current. Overall, the model is able to capture significant kinetic features of IT-SOFCs, and allows to gain insight into relevant parameters for the optimal design of the cell (electrochemically active thickness, current and potential distribution, mass diffusion gradients). Samaria doped Ceria (SDC) and Gadolinia doped Ceria (GDC) are reference electrolyte materials for intermediate temperature solid oxide fuel cell (IT-SOFC) applications, thanks to their high ionic conductivity between 500• C and 700• C. 1-5 Associated to a high ionic conductivity, however, these materials show mixed ionic and electronic conductive (MIEC) properties, and their electronic conductivity increases when exposed to reducing atmospheres. The MIEC character of the electrolyte, in turn, results in the onset of electronic leakage currents (or short circuit currents) and low open-circuit voltage values. The leakage current has a chemical origin and is due to the partial reduction of Ce 4+ ions to Ce 3+ ions, prompted by the different chemical potential at the electrodes: this current is active also in the absence of an electric field applied on the cell, since it stems from the spontaneous transfer of ions across the lattice structure. As a consequence, the effects of the leakage current are not confined to the electrolyte, but extend to the electrodes, and entail a complex relationship with the current drawn from the cell. 6 Deeper insight can therefore be achieved by mathematical modeling.In the literature, comprehensive models can be found, which take into account the MIEC properties of Ce-based electrolytes. Starting from continuum rigorous descriptions, a series of models has been derived for the prediction of impedance spectra collected on MIEC electrolytes, the most important examples being those by Jamnik and Maier, 7 by the group of Haile 8,9 and by Atkinson et al. 10 These models propose closed-form, equivalent circuit-l...

show abstract

Section: Impedance Experiments At 700mentioning

confidence: 71%

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

Rahmanipour

Pappacena

Boaro

et al. 2017

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…The two low frequent processes P1 and P2 show the properties of concentration polarization as describes in (7,8). P1 is caused by the diffusive mass transport in the flow channels of the flow field, whereas P2 can be attributed to the diffusion in the contact meshes (8).…”

Section: Resultsmentioning

confidence: 96%

“…P1 is caused by the diffusive mass transport in the flow channels of the flow field, whereas P2 can be attributed to the diffusion in the contact meshes (8). The higher frequent parts of the spectra are not affected by concentration polarization.…”

Section: Resultsmentioning

confidence: 96%

Towards Understanding the Impedance Response of Ni/YSZ Anodes

Sonn¹,

Leonide²,

Ivers‐Tiffée³

2007

ECS Trans.

Self Cite

View full text Add to dashboard Cite

A comprehensive impedance study on the hydrogen oxidation in Ni/8YSZ cermet anodes has been realized in consideration of a broad range of operating conditions. A major problem in this respect concerns the origin and physical interpretation of empirical 'equivalent circuits' used to fit the experimental data. We applied a two-stage approach for the evaluation of the impedance data: I) at first by the deconvolution of a distribution function of relaxation times (DRT) four different processes and their characteristic relaxation times have been identified. Two parts at frequencies <1 kHz represent a gas-conversion process or respectively a gas diffusion, whereas two parts at higher frequencies (2-30 kHz) are associated with the electro-oxidation of hydrogen at active sites. II) Subsequently the last mentioned processes were fitted to a "transmission line" model describing the electronic and ionic transport properties of the Ni/8YSZ cermet. This approach resulted in the determination of 1) the total ionic conductivity of the Ni/8YSZ cermet and 2) the spatial extension of the electrochemical active area adjacent to the electrolyte/electrode interface. Pre-Identification of Impedance DataIt is often a questionable and fraught task to use equivalent circuit models for the evaluation of EIS data when the number and nature of physical processes that contribute to the overall impedance are not known. This especially holds true for technical electrode structures that often do not allow a detailed modelling because of their complex interfacial geometries. Therefore we use a pre-identification method based on the "Distribution Function of Relaxation Times". This method separates polarisation processes with different time constants directly from impedance data (1). Distribution Function of Relaxation Times (DRT)In the simplest case a polarization process in an electrochemical system can be described by an equivalent circuit made of a parallel connection of an ohmic resistance R and a capacitance C. This process is characterised by its time constant ( )

show abstract

“…Recently, a number of authors have modeled the impedance of solid oxide fuel cells ͑SOFCs͒ based on a detailed description of the governing physicochemical processes ͑chemistry, transport, and electrical properties͒. [8][9][10][11][12][13] This approach allows a physically based assignment of impedance features to the underlying processes. It therefore yields a much more detailed understanding of the electrochemical system than the use of equivalent circuit models.…”

mentioning

confidence: 99%

Rapid Impedance Modeling via Potential Step and Current Relaxation Simulations

Bessler

2007

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

We present a fast computational technique for the electrochemical impedance of solid oxide fuel cells ͑SOFCs͒ based on detailed electrochemistry and transport models. The technique is based on the transient numerical simulation of a fast, submicrosecond potential step followed by current relaxation. The impedance is reconstructed by applying a Fourier transform to the resulting current and potential traces. The successful application of this technique is based on the combination of ͑i͒ numerical time integration of the governing equations using a time-adaptive solution algorithm, and ͑ii͒ a Fourier transform algorithm for arbitrarily spaced time points. Results are presented for a two-dimensional model of a symmetrical SOFC including gas-phase transport, pore phase transport, surface chemistry, and elementary kinetic charge transfer. Calculation speed is increased by a factor of 10-200 in comparison to a conventional simulation technique based on frequency-resolved sinusoidal excitation, depending on the frequency resolution of the conventional technique and the imposed precision of the numerical solver. The technique is an important tool for a model-based interpretation of experimental impedance data without using equivalent circuits.

show abstract

Experimental and Modeling Study of the Impedance of Ni/YSZ Cermet Anodes

Cited by 24 publications

References 21 publications

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

Towards Understanding the Impedance Response of Ni/YSZ Anodes

Rapid Impedance Modeling via Potential Step and Current Relaxation Simulations

Contact Info

Product

Resources

About