An Electrochemical Model of a Solid Oxide Fuel Cell Using Experimental Data for Validation of Material Properties

Abstract

This paper reports an electrochemical model of a Solid Oxide Fuel Cell where the model is compared against experimental data using the results from a button cell electrical test. The model fits the experimental data reasonably well using material properties found in the literature. Some of the material properties were used as fitted parameters to improve the fit, and their values compared with reported measured values. Further, cell polarization losses are explored to determine which one influences the voltage-current density characteristics the most. In comparing the material properties found in the literature with the one appropriate for the model curve fit to the experimental results, some discrepancies were observed. Hence, a better methodology is needed to understand the actual cell behavior and where improvements are needed. The method developed here is very useful for a commercial supplier of Solid Oxide Fuel Cells where button cells taken from a batch can be used to determine how good the cells are before they are installed in a stack.

Solid Oxide Fuel Cell Performance Analysis through Local Modelling

“…The pre-exponential coefficients are specific to the electrocatalytic materials used (i.e., Ni/8YSZ-cermet as anode and LSCF as cathode), yet the detected values are comparable with the range in the literature (γ an 5.5 × 10 8 − 5.5 × 10 10 A/m 2 , γ cat 7 × 10 8 − 7 × 10 10 A/m 2 ) [30]. The requested parameters for concentration overpotential are presented in previous works [31,33], while the micro-structural cell features are derived from post-experimental characterization of different layers (refer to Section 4.4).…”

Optimization of a Reference Kinetic Model for Solid Oxide Fuel Cells

“…Indeed, resistances due to reaction development are relevant at a low current, while component diffusion mechanisms are the rate-limiting step under a high load. The charge transfer coefficients are usually assumed to be 0.5 (equal requested energy for forward and backward process) because electrode material is a good catalyst for both reactions [14]. Neglecting the concentration gradient between bulk and TPB at a low load, the activation overpotential (Equation 23) is written according to the hyperbolic sine form [13]:…”

“…In Equation (49), the molecular diffusivity is taken into account for a gas binary mixture on the basis of diffusion coefficient D i−j (Equation (50)), weighted on molar fractions (Equation (51)) [24]. Specifically, the molecular diffusion coefficient D i−j is calculated using the Fuller approach for binary system [14]:…”

“…Nonetheless, the first two are effective only at low and high overpotential, respectively [13]. Thereby, the hyperbolic sine equation is commonly used, assuring a wider validity range [5,10,14]. The activation polarization contribution is a function of the rate between effective and equilibrium current density.…”

“…According to the literature, this last term is expressed through several operating parameters. The equilibrium current density can be a constant value obtained by experimental data fitting [14], depending on temperature [5,10] and components composition [1,15]. More specific approaches introduce TPB length to underline electrocatalyst performance [11] or to evaluate composition dependence, considering the rate-limiting step of electrochemical reactions [16].…”