Fabrication of Solid State Ionic Devices Using Additive Manufacturing

Abstract

The fabrication of solid state ionic devices requires customization of size, shape, geometry, and composition for various components. Traditionally used fabrication methods are tape casting and screen printing. Although these methods are well developed they are difficult, time consuming, and costly to adjust to fit particular device requirements. Sandia National Laboratory has recently developed Robocasting, an additive manufacturing technique that was developed as a method that allows for the adaptation needed to rapidly prototype specialty ceramics in a more economically efficient way. Robocasting is currently used commercially to produce complex ceramic parts that are used in various applications including catalyst supports and casting filters. The technology has not been developed for the fabrication of ceramic electrochemical devices. While this has worked well for these limited specific needs, this technology has been optimized primarily for alumina based ceramic materials. In order to expand the versatility of this method for solid state ionic devices, powder precursors of solid electrolytes and electrode materials with specific properties must be developed. Tailoring the rheology of the pastes and slurries used in this extrusion method is an important aspect that determines the resolution of the resulting ceramic components. Another challenge is controlling the residual stress and shrinkage through the material properties of various components. We have applied this additive manufacturing technique to our unique design of gas sensors. These multi-component sensors consist of a yttria-stabilized zirconia substrate onto which a set of three solid electrodes and a porous YSZ electrolyte are deposited. The production method employed involves the direct printing of a suspended powder of the electrode and electrolyte components using Robocasting technology. This allows for the rapid prototyping of these devices. The key to this process is the use of high temperature co-fired ceramics which enables all components to be fired together. The electrodes consist of a platinum counter electrode and lanthanum-strontium-chromite and gold-palladium working electrodes. By taking advantage of the dissimilar electrochemical catalytic activity of these materials, the difference in mixed potential between two electrodes can be used to quantify the concentration and discriminate the type of gas present. These devices are capable of detecting NOx, hydrocarbons, H2, and NH3 at concentrations on the order of parts per million. Figure 1