SOFC Modeling and Parameter Identification by Means of Impedance Spectroscopy

Abstract

A zero-dimensional stationary model for the I-U characteristics of anode-supported solid oxide fuel cells (SOFC) is presented. The different kinds of electrode polarization resistances are separated from experimental impedance data by means of a detailed equivalent circuit model specified for anode-supported cells. This has the big advantage that partial pressure and temperature dependency of electrode exchange current densities could be determined by a fit of semi-empirical power law model equations. For the first time, the exponents a and b for the pH2- and pH2O-dependency of the anodic exchange current density are obtained independently. Equally, the exponent m for the pO2-dependency of the cathodic exchange current density is derived. The anodic and cathodic gas diffusion polarization is calculated without the estimation of parameters such as tortuosity and porosity. Our approach is advantageous to separate anodic and cathodic activation and diffusion polarization and precisely predicts I-U characteristics for a wide operating range.

Three-dimensional printed yttria-stabilized zirconia self-supported electrolytes for solid oxide fuel cell applications

“…The optimum attachment temperature of both electrodes was determined, with especial attention to the one of the cathode side, after systematical evaluation of the polarization resistance in symmetrical cell configuration (not presented here for conciseness reasons). Area specific resistances of ASR=0.4 Ωcm 2 and ASR=0.2 Ωcm at 900ºC and activation energies of Ea=1.12±0.04 eV and Ea=1.43±0.02 eV were 2 obtained for the optimized anode and cathode layers, respectively, being in reasonable agreement with the literature [43] [44]. A detail of the attachment of a typical cathode to the electrolyte layer is presented in Figure 2c showing the good connnectivity required to ensure a high performance in SOFC mode.…”

Evaluation of electrochemical impedance spectra by the distribution of relaxation times

“…More details on the analytical calculation of the DRT of these equivalent circuit elements and a comparison of the analytical and numerical result are discussed in. 46) The impedance of an RQ-element (the parallel connection of resistance and constant phase element Q) is given by:…”

“…with the corresponding DRT, a complex valued function with a singularity at x = ln(1/t chem ): which can be simplified 46) to: …”

“…(9) would probably deliver a more definitive conclusion about the correct analytical DRT-expression of a Gerischer-impedance. 46) …”

ELECTRODOS AVANZADOS PARA PILAS DE COMBUSTIBLE DE ÓXIDO SÓLIDO (SOFCs)

“…Los datos se han representado en configuración tipo Arrhenius. [123] , ambas series de parámetros se pueden comparar directamente, puesto que este material es rico en electrones [124,125] o huecos electrónicos.…”