Mechanical and electrical properties Ge and Gd co-doped CeO2-based electrolyte for intermediate-temperature solid oxide fuel cells

This study utilizes the citric acid-EDTA combustion method to synthesize Gd0.1Ce0.9-xGexO1.95 (x = 0.005,0.01,0.04,0.07), marked as nGGDC (n = 0.5,1,4,7), and Gd0.1Ce0.9O1.95 (10GDC) composite materials, focusing on electrochemical performance and mechanical properties. The prepared materials all form a cubic fluorite structure. Doping with Ge4+ increased the densification of the electrolyte, enlarged the grain volume, and reduced the number of grain boundaries, thereby enhancing the dielectric constant. This improvement reduces intragranular resistance and grain boundary resistance, promoting the migration of oxygen ions. The Scavenging Ratio (SR) of Gd0.1Ce0.89Ge0.01O1.95 (1GGDC) is the highest, reaching 4.1 at 975 K, and the Blocking Factor (partial derivative(t)) of 1GGDC decreases by 52 % compared to 10GDC. 1GGDC exhibits the highest conductivity and the lowest activation energy, increasing by 424% and decreasing by 20% compared to 10GDC, respectively. In terms of mechanical properties, compared to 10GDC, 1GGDC samples exhibit improved hardness (10.85 GPa), fracture toughness (3.18 MPa m(1/2)), and flexural strength (97.62 MPa). Electrolyte single cells containing 1GGDC demonstrate higher power density and current density, particularly at 1023 K (955 mW/cm(2) vs. 740 mW/cm(2) for 10GDC). According to density functional theory calculations, the oxygen vacancy formation energy, binding energy, and migration barrier of GGDC electrolyte co-doped with Ge and Gd are all lower than those of GDC. Therefore, 1GGDC can be considered as a potential intermediate-temperature solid oxide fuel cells (IT-SOFCs) electrolyte material.