Solid Oxide Membrane for Reduction of Ce0.8Gd0.2O2 and TiO2 in LiCl-Li2O

A solid oxide membrane was used in a three electrode electrochemical cell to separately reduce, both Ce_0.8Gd_0.2O₂ and TiO₂ in molten solution of LiCl-Li₂O.  The Ce_0.8Gd_0.2O₂ was used as a surrogate for UO₂, with the goal of using a similar technique during potential nuclear fuel reprocessing scenarios. The solid oxide membrane was a closed-end yttria stabilized zirconia tube inserted in an electrochemical cell with an argon cover gas.  A tungsten electrode was used as a quasi reference, and a graphite basket was used to separately hold both Ce_0.8Gd_0.2O₂ and TiO₂ powders. One end of the YSZ tube was held at room temperature, while the closed end was submerged in the molten salt at 650 °C. A platinum bearing paint coated the inside of the SOM and facilitated electrical contact from the nonconductive cold region to the conductive hot region.  Argon gas was swept through the solid oxide membrane and an oxygen detector, where the oxygen pumped through the membrane during reduction was monitored.  Initial oxygen evolution was measured using the oxygen meter and readings were observed to correlate to reduction of the Ce_0.8Gd_0.2O₂ and TiO₂ as determined from electrochemical data.  The reduced Ce and Ti oxides were examined post experiment via SEM, EDS, and XRD.  EDS and XRD were used to prove partial reduction in both the Ce_0.8Gd_0.2O₂ and TiO₂, but complete reduction to the metallic state was not observed for either oxide to date.  EDS analysis found reduction of the TiO₂ to as low as Ti­_0.8O_0.2 (with trace Cl, Li could not be detected).  EDS analysis of the Ce_0.8Gd_0.2O₂ found evidence of reduction to Ce_0.8Gd_0.2O (with trace Cl, Li not detected).  XRD found evidence of LiTiO₂, LiTi₂O₄, and (Li_0.54Ti_2.86)O₆ from the TiO₂ basket/electrode.  Analysis of reduced products may have been impacted from air exposure during analysis.  Fragility of the electrode basket used for the TiO₂ experiment was believed to be the limiting factor in achieving reduction, and further experiments are ongoing using a more robust metallic basket/electrode design.