Unravelling the synergistic effect on ionic transport and sintering temperature of nanocrystalline CeO2 tri-doped with Li Bi and Gd as dense electrolyte for solid oxide fuel cells

Abstract Microstructural and electrochemical investigations of tri-doped (Gd, Li and Bi) cerium oxide, with theoretical formula Ce0.8(1-x-y)Gd0.2(1-x-y)LixBiyO[1.9(1-x-y)+x/2+3y/2] (x = 0.02 or 0.03 and y = 0.03 or 0.02 and x+y = 0.05) were carried out by XRD, BET, SEM, Raman, and EIS analyses. According to the dilatometer analysis, the synergistic combination of lithium and bismuth promotes the reduction of sintering temperature down to 800-900°C. A densification >95% was achieved for the electrolytes sintered at 900°C. Raman analysis, in agreement with XRD, demonstrated that the lithium and bismuth induced changes due to the growth of the topological disorder and a higher defectiveness provoked by doping. The high dopant concentration (5 mol%) is well distributed into the lattice and forms a complex network of defects that traps the oxygen vacancies and hence mobile ions promoting the ionic transport. As compared to a single (CGO) or a bi-doped system (BiCGO and LiCGO) an improvement of total conductivity was achieved at lower sintering temperature, with a maximum value for Ce0.76Gd0.19Li0.03Bi0.02O1.85 of 2.68·10-3-1.66·10-1 S cm-1 in temperature range of 400-800°C.