Optimization of safe doping level for enhanced CO2 flux in composite membrane

Abstract

Rare earth doped oxides have been intensively promoted for the last two decades to embrace the high-performance target of a ceramic–carbonate composite CO₂-separation membrane, with countless incidents of exsolution. Unfortunately, information about securing a safe doping limit in the above case is unavailable in the public domain. Herein we provide a first report, where an answer to this question is rigorously attempted. Thus, the study demonstrates a maximum safe level of doping in a Ce_1−XGd_XO_2−δ–LiNaCO₃ (80 : 20 vol%) composite, where X = 0.10, 0.15 or 0.20. The required sets of ceramic matrix powders were prepared using the Pechini method and consolidated at 1500 °C, with intermediate powder coarsening. The composite membranes were obtained by impregnating these matrices with LiNaCO₃ at 700 °C. The impedance measurement illustrated the highest bulk and total conductivity, at 250 °C, in composites with 10 mol% and 15 mol% of Gd doping, respectively. CO₂-separation followed the trend in total conductivity, with highest flux of 0.14 cm³ min⁻¹ cm⁻² at 650 °C for 15 mol% Gd. Post-mortem analysis showed the precipitation of Gd and evaporation of the melt with retention of carbon allotropes on the sweep face of the membrane of 20 mol% Gd. In short, this work gives some insight into optimizing rare earth Gd-doping for improved the performance of a composite CO₂-separation membrane.