Applications of rare earth doped complex oxides in potentiometric sensors, solid oxide full cells, and thermoelectrics

Abstract

Rare-earth doped complex oxide materials have a number of interesting applications in the clean energy economy. By tailoring the materials composition, the electronic, thermal, and ionic transport properties can be tuned for the intended application. In this study, three examples of such applications are considered. First, a crystal structure known as sodium super ionic conductors (Na1+3xZr2(P1-xSixO4)3 ) was modified to synthesize a cerium super ion conductor [Ce.1Zr.9)40/39Nb(PO4)3]. Tuning the composition resulted in a complex oxide that has been shown to have selective cerium ion conductivity, making it a candidate as a solid electrolyte in a real time rare earth ion sensor. These sensors were successfully applied to demonstrate real time monitoring of cerium concentrations in aqueous solutions and could potentially be modified to detect other rare earth elements, eliminating the time intensive chemical assay testing currently used in rare earth recycling and refining. Another application of complex oxides includes the use of lanthanum doped strontium manganese oxide (La.8Sr.2MnO3) as an electronically conductive diffusion barrier. This material was applied to 2205 stainless steel to test its potential as an interconnect in solid oxide fuel cells (SOFCs). These barrier layers can reduce high temperature oxidation and spallation in SOFCs interconnects, potentially increasing the lifetime of SOFC stacks, and allowing for cheaper ferrous alloys to be used in operating conditions up to 800°C, further lowering the overall cost of SOFCs. Lastly, gadolinium doped strontium titanate (Gd.08Sr.92TiO3) is considered as a thermoelectric material. Specifically the addition of a second phase of gadolinium doped cerium oxide (Gd.2Ce.8O3-δ) was used to achieve enhancements in the thermoelectric properties.