Abstract
The growth of 3D printing has opened the scope for designing microstructures for solid oxide fuel cells (SOFCs) with improved power density and lifetime. This technique can introduce structural modifications at a scale larger than particle size but smaller than cell size, such as by inserting electrolyte pillars of ∼5–100 μm. This study sets the minimum requirements for the rational design of 3D printed electrodes based on an electrochemical model and analytical solutions for functional layers with negligible electronic resistance and no mixed conduction. Results show that this structural modification enhances the power density when the ratio keff between effective conductivity and bulk conductivity of the ionic phase is smaller than 0.5. The maximum performance improvement is predicted as a function of keff. A design study on a wide range of pillar shapes indicates that improvements are achieved by any structural modification which provides ionic conduction up to a characteristic thickness ∼10–40 μm without removing active volume at the electrolyte interface. The best performance is reached for thin (<∼2 μm) and long (>∼80 μm) pillars when the composite electrode is optimised for maximum three-phase boundary density, pointing toward the design of scaffolds with well-defined geometry and fractal structures.
Highlights
Flat electrode: the benchmark.—It is worth analysing the electrochemical performance of a flat electrode because any improvement provided by a mesoscale structural modification must be evaluated in comparison with the current density that a benchmark flat electrode would exhibit in the same conditions
The benefits of a mesoscale modification would be amplified, since min Remdin decreases as keff decreases. This implies that a composite electrode intended for mesoscale structural modification should be optimised for maximum three-phase boundary (TPB) density rather than for maximum keff, because the effective ionic conduction is provided by the ion-conducting pillars
The rational design of the electrode/electrolyte interface, here referred as mesoscale structural modification, in solid oxide fuel cells (SOFCs) porous composite electrode functional layers was addressed through modelling means for the limit case of negligible electronic resistance and no mixed ionic-electronic conduction
Summary
The values obtained from the application of Eqs. 7–9 are an approximate solution of the 2D model reported in the Model equations section. Eqs. 7–9 allow for a quick estimation of the current density by analytical means, providing an accurate assessment of the upper bound of performance as discussed later
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