Determination and validation of polarization losses parameters to predict current/voltage-characteristics for SOFC button cell

Abstract

Solid Oxide Fuel Cell represents a valid and clean alternative to conventional combined heat and power systems. These devices can convert different kinds of fuels into electricity with high efficiencies (up to 75–80 %) and low CO2 or hazardous emissions. In order to understand and validate Solid Oxide Fuel Cell behavior at different operating conditions, investigations are currently focusing their attention on modeling. In this work, an experimental-based model to study the effect of different hydrogen and temperature conditions on both the polarization processes and its effect on Solid Oxide Fuel Cell performance is presented. Experimental parametric campaigns were carried out using a button anode supported Solid Oxide Fuel Cell with an active area of about 2 cm2. A practical zero-dimensional mathematical model based on low and high voltage approximations of the Butler-Volmer equations was used starting from an experimental current–voltage dataset to obtain polarization curve parameters representing different physical phenomena associated with the cell. To validate the obtained results and gain additional information, electrochemical impedance spectroscopy measurements and distribution of relaxation times analysis were performed both in open circuit voltage and underload at 0.5 A/cm2. Finally, from the fitted parameters, it was possible to derive dimensionless charge transfer coefficients related to the most probable reaction mechanisms occurring in the cell, equal to 2 for the anodic process and 3.5 for the cathodic process. Moreover, from the results the obtained exchange current densities range from 0.024 A/cm2 to 0.048 A/cm2 for O2 reduction and from 0.012 A/cm2 to 0.073 A/cm2 for H2 oxidation and subsequently, the activation energies equal to 100 kJ/mol and 66 kJ/mol for anodic and cathodic electrochemical processes, respectively.