Design and 3D Printing of Controllable and Gradient Porous Supports for Solid Oxide Fuel Cells

Abstract

A controllable and gradient porous structure is desirable for many applications including solid oxide fuel cells (SOFC) electrodes. A SOFC contains a minimum three basic ceramic thin films with a thin yet dense electrolyte layer separates the adjacent porous anode and cathode layers. In general, the thinner the electrolyte layer, the smaller the ohmic resistance would be. The anode and cathode layers need to be porous so to allow gases (e.g. H2 and O2) to easily penetrate to the triple-phase boundary (TPB). At the same time the anode and cathode layers serve as the paths of removing the electrons generated at the TPBs. Properly design and fabricated porous electrode microstructure could greatly increase the connectedness of gas, electrons and/or protons/oxygen ions, and therefore reduce the gas diffusion and ohmic resistances of the SOFC electrodes and boost the overall fuel cell performance.Although there are electrolyte- and cathode- supported SOFC developers, the most used configuration is anode-supported or additional component-supported, for example metal-supported or ceramic-supported with a planar or tubular geometry. Conventionally, the porosity is generated by using sacrificial templates or pyrolyzable pore-formers for pore formation. Pores are formed after the burning off these sacrificial templates or pyrolyzable pore-formers at elevated temperatures. The size, shape and amount of the pore-formers can be controlled. However, the connectivity and orientation of these pores are not easily controllable, leaving significant amount of closed and isolated pores. These isolated and/or closed pores do not contribute to the TBP. Freeze casting of water-based suspension slurries could generate aligned pores, the low connectivity and weak mechanical strength challenges remain.This paper focuses on the design and fabrication of a desired gradient porous microstructure for use as a SOFC support. The pore size and shape, porosity and connectivity could be determined and strictly controlled by design. Tubular and planar parts with metal, cermet and/or ceramic materials are to be fabricated. Additive manufacturing (AM, or 3D printing) process enables the fabrication of the complicated parts with the desired microstructure directly from the computer-aided design (CAD) models. The morphology, porosity, permeability and tortuosity of the 3D printed parts are investigated and results are discussed.