Fabrication of Tubular Ceramics Consisting of a Solid Electrolyte and Various Thin Film Ceramic Membranes By Rotational Additive Manufacturing (RAM)
Authors: Emley Benjamin , Yao Yan 
Published: February 2020

Fabrication methods to make low cost, tubular multi-layered ceramic structures are of great interest for producers of solid oxide fuel cell (SOFC) technology.  Effort in the art of manufacturing SOFC technology over the past 20+ years has given rise to multiple methods of making SOFC structures that have exhibited a range of power densities and have demonstrated reduced degradation of performance over long operating times (>1,000 hours).  The development of multiple geometry-types for the SOFC unit cell as well as various materials sets have also evolved in an effort to reduce fabrication costs and/or increase the lifetime of a working cell under a constant electrical load.  The recent development of “stacking” ceramic films as layers in the shape of a ceramic tube has recently been demonstrated to significantly reduce the overall time and cost of making SOFC structures also while improving performance of the SOFC compared to conventionally manufactured SOFC tubes.   The method, referred herein as Rotational Additive Manufacturing (RAM), is a process of printing ceramic inks onto a spinning, cylindrical mandrel which is later removed after the printing process is completed.  The composition of each layer is controlled by selecting materials from different reservoirs that feed into the nozzle of the printer.  The result is a tailored, multi-layered, ceramic tube using one processing strategy consisting of stacked layers as thin as 0.5 microns each, and a controlled composition within each layer of almost limitless compositional varieties.  The layer thickness per “pass” of the print head can be much higher than 0.5 microns and is simply a function of the deposition rate of materials sent to the nozzle of the printer.   Increasing the thickness of each layer is useful when printing the bulk support material of the tubular structure.  Additionally, the process is especially useful for grading the interface between different functional layers of an electrochemical cell providing for an economical approach to providing for the most ideal interface (controlled porosity, minimized thermo-mechanical differences, and optimized electrical/ionic conduction pathways) between functional layers such as the anode and the electrolyte interface of a SOFC unit cell.  Porosity, particle size/ surface area of materials, and composition can be easily controlled and changed from layer to layer as required. 

Complete, tubular SOFCs consisting of a zirconium based electrolyte, lanthanum ferrite based cathode in perovskite form, and a nickel-zirconium cermet anode have been fabricated using the RAM process by a private developer.   No known special processing parameters for the compositional grading of these cells have been disclosed, but the overall performance has been reported to be significantly greater than that of conventionally processed tubular cells consisting of similar material sets.  The power density of cells using the RAM method has been reported to be as much as five times (2 Watts per cm2 vs. 400 mW per cm2; RAM cells vs. extruded cells) as well as an improvement of gravimetric power density as much as 144% (2.2 Watts per gram of the unit cell vs. 0.9 Watts per gram).  These results were reported for cells operating at 800 oC and using hydrogen gas and air as the fuel.  It is important to note, also, that the total thickness (active + bulk support layer(s)) of the SOFC produced using the RAM method is much thinner than that of conventionally extruded SOFCs, and it was reported that the RAM provides this unique capability which is limited with conventional methods.

This project was initiated in joint collaboration with the developer of RAM to help understand the fundamental explanations for the increased performance of tubular SOFCs produced using the RAM method.  Several analytical techniques have been completed that analyze the performance of cells made from both RAM strategies as well as conventional means and provide insight to such differences in maximum performance.  Furthermore, we provide additional insight to further improve the performance of tubular SOFCs made using RAM by optimizing the gradation between the functional layers and by introducing new material sets of the SOFC.