Validation of a physically-based solid oxide fuel cell anode model combining 3D tomography and impedance spectroscopy

A Bertei,E Ruiz-Trejo,F Tariq,V Yufit,A Atkinson,N.P Brandon

doi:10.1016/j.ijhydene.2016.09.100

A Bertei, E Ruiz-Trejo + Show 4 more

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https://doi.org/10.1016/j.ijhydene.2016.09.100

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Abstract

This study presents a physically-based model for the simulation of impedance spectra in solid oxide fuel cell (SOFC) composite anodes. The model takes into account the charge transport and the charge-transfer reaction at the three-phase boundary distributed along the anode thickness, as well as the phenomena at the electrode/electrolyte interface and the multicomponent gas diffusion in the test rig. The model is calibrated with experimental impedance spectra of cermet anodes made of nickel and scandia-stabilized zirconia and satisfactorily validated in electrodes with different microstructural properties, quantified through focused ion beam SEM tomography. Besides providing the material-specific kinetic parameters of the electrochemical hydrogen oxidation, this study shows that the correlation between electrode microstructure and electrochemical performance can be successfully addressed by combining physically-based modelling, impedance spectroscopy and 3D tomography. This approach overcomes the limits of phenomenological equivalent circuits and is suitable for the interpretation of experimental data and for the optimisation of the electrode microstructure.

Highlights

Solid oxide fuel cells (SOFCs) are electrochemical systems which convert the chemical energy of a fuel, such as hydrogen, directly into electric energy and heat, allowing for high efficiency of power generation [1,2], low emission of pollutants [3] and fuel flexibility [4]
This study describes the validation of a physically-based electrochemical model by using impedance spectroscopy data for different operating conditions and different electrode microstructures
At 700 C the i0TPB fitted in this study for Ni:scandiastabilized zirconia (ScSZ) is equal to 46.0$10À6 A mÀ1, while in Ni:yttria-stabilized zirconia (YSZ) anodes the i0TPB is 27.5$10À6 or 3.8$10À6 A mÀ1 according to Bieberle et al [87] or de Boer [86], respectively, for 97% H2e3% H2O

Summary

Introduction

Solid oxide fuel cells (SOFCs) are electrochemical systems which convert the chemical energy of a fuel, such as hydrogen, directly into electric energy and heat, allowing for high efficiency of power generation [1,2], low emission of pollutants [3] and fuel flexibility [4]. The performance and durability of the cell are strongly dependent on the electrodes [5e7], which are porous layers, typically made of a composite of ceramics and/or metallic particles, wherein electrochemical reactions occur. Understanding how the microstructure affects the electrochemical response would allow researchers to better design the electrodes to increase power density and extend lifetime [13e17]. This task can be accomplished by using physically-based models. The continuum approach is adopted in developing electrochemical models [19,29e31] In this approach the particle-level details are represented through effective microstructural properties, which can be obtained from the application of empirical correlations [32], percolation models [33e35], packing algorithms [36,37] or 3D tomography [38]. Several modelling studies have been presented to predict the microstructural contribution to electrochemical performance and enhance the power density via an optimisation of the microstructural properties [19,37,39e43]

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