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 similar to 5-100 mu m. 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 k(eff) 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 k(eff). 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 similar to 10-40 mu m without removing active volume at the electrolyte interface. The best performance is reached for thin (similar to 80 mu m) 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. (c) The Author(s) 2016. Published by ECS.