Proteic sol–gel synthesis of Gd-doped ceria: a comprehensive structural, chemical, microstructural and electrical analysis

Gd-doped ceria (Ce_1−xGd_xO_2-δ; x = 0, 0.1 and 0.2) is one of the best ceramic electrolytes for application in solid oxide electrochemical devices. This work reports an innovative and environmentally friendly route known as “proteic sol–gel synthesis” using gelatin for their preparation. Materials are characterized via thermogravimetric analysis, X-ray diffractometry, scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, and electrochemical impedance spectroscopy. The proposed method allows to produce pure phase nanosized powders at 400 °C that exhibit excellent sinterability at 1350 °C. Significant differences are found in the bulk at lower temperatures, with estimated defect association enthalpies of 0.45 and 0.56 eV for the compositions containing 10 and 20 mol% Gd, respectively, leading to an increased bulk conductivity in the first case. In contrast, identical grain boundary Schottky barrier height values of around 0.2 V are a possible result of the relatively low sintering temperature, decreasing the extent of the acceptor dopant segregation to the grain boundaries due to insufficient cation mobility. This leads to similar specific grain boundary characteristics in both doped compositions. Overall, this work provides a rational understanding of a novel route for the synthesis of CGO ceramics with competitive performance and decreased sintering temperature.