The Effect of Electrode Morphology on Solid Oxide Fuel Cell Performance

Abstract

The morphology of the active electrode in a solid oxide fuel cell has a strong impact on both the transport properties and the active triple phase boundary length and distribution. The performance of the electrode emerges from the interaction of these two parameters and is impacted strongly by the size and shape of the starting powders used to make the ionically and electronically conducting phases of the electrode as well as by the manufacturing method used and the sintering process post manufacture. This paper presents a numerical study over a range of electrode morphologies chosen to represent different manufacturing processes and presents comparisons of geometric characteristics, transport properties and electrode performance. Three different morphologies are generated from three different starting powders, spheres representing non aggregated powders, agglomerates of spheres and high aspect ratio cylinders modelling splats formed in plasma sprays. Of particular interest in this study is the effect of anisotropy of the base particles on the resulting electrode. For each base particle shape multiple stochastic realizations of densely packed particle systems are generated using a collective rearrangement algorithm. The structures are then analysed geometrically with methods from spatial statistics using our own Java-based software, and meshed, solved and analysed with respect to transport and performance using a custom modified version of the open source computational fluid dynamics package, openFOAM. Detailed comparisons are presented in terms of tortuosity of paths through each phase of the material, constrictivity and chord lengths in different directions, directional transport properties in each of the three phases, distribution of the triple phase boundary lines and electrode performance