Modeling Analysis of Bi-Layer Ni-(ZrO2)x(Y2O3)1−x Anodes for Anode-Supported Intermediate Temperature-Solid Oxide Fuel Cells

Anna Enrico,Marco Cannarozzo,Paola Costamagna

doi:10.3390/en7095647

Abstract

Intermediate temperature-solid oxide fuel cell (IT-SOFC) Ni-(ZrO2)x(Y2O3)1−x (Ni-YSZ) anodes formed by two layers, with different thicknesses and morphologies, offer the possibility of obtaining adequate electrochemical performance coupled to satisfactory mechanical properties. We investigate bi-layered Ni-YSZ anodes from a modeling point of view. The model includes reaction kinetics (Butler-Volmer equation), mass transport (Dusty-Gas model), and charge transport (Ohm’s law), and allows to gain an insight into the distribution of the electrochemical reaction within the electrode. Additionally, the model allows to evaluate a reciprocal overall electrode resistance 1/Rp ≈ 6 S·cm−2 for a bi-layer electrode formed by a 10 µm thick active layer (AL) composed of 0.25 µm radius Ni and YSZ particles (34% vol. Ni), coupled to a 700 µm thick support layer (SL) formed by 0.5 µm radius Ni and YSZ particles (50% vol. Ni), and operated at a temperature of 1023 K. Simulation results compare satisfactorily to literature experimental data. The model allows to investigate, in detail, the effect of morphological and geometric parameters on the various sources of losses, which is the first step for an optimized electrode design.

Highlights

Solid oxide fuel cells (SOFCs) offer an electrochemical energy conversion technology featuring high efficiency and low pollution emissions
Our simulation results for φel,active layer (AL) = 0.55 are in agreement with literature data reporting that an increase of the AL thickness over 10 μm is practically non-influential, but the explanation we propose for this behavior is different from that reported in the literature, since simulation results show that increase of the AL thickness does not modify any of the sources of losses, neither activation nor diffusive
Even if our results suggest that bi-layered electrodes with thin support layer (SL) display better electrochemical performance, the choice of geometrical and morphological parameters of the SL must be made taking into account the electrode electrochemical performance, and the desired mechanical features

Summary

Introduction

Solid oxide fuel cells (SOFCs) offer an electrochemical energy conversion technology featuring high efficiency and low pollution emissions. Their reliability, modularity, and fuel adaptability make them good candidates for substituting, at least in some applications, more conventional energy conversion systems [1,2,3,4,5,6]. Lowering the operating temperature lowers the fuel cell performance, since the kinetics of the electrochemical reaction decreases rapidly as temperature decreases. The electrodes and electrolyte materials become less conductive [8], leading to higher ohmic losses. Considering the overall cell performance, the ohmic losses are dominated primarily by the electrolyte contribution [9]

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Results

Conclusion