Gd0.1Ce0.9-xGaxO2-δ (x = 0, 0.04,0.07, 0.12) are synthesized via the citric acid-EDTA combustion method as an electrolyte material for intermediate-temperature solid oxide fuel cells. XRD and Rietveld refinement revealed that the material exhibits a single-phase cubic fluorite structure. SEM and EDS analyses demonstrated that the incorporation of Ga ions improved the sample's density, increased the grain size, and provided better element dispersion. XPS analysis confirms that Ga-Gd co-doping leads to increased oxygen vacancy concentration and modifies the oxidation states of Ce. Impedance spectroscopy results indicated that Ga-Gd co-doped ceria has higher ionic conductivity and lower activation energy compared to Gd single-doped ceria. In comparison to Gd0.1Ce0.9O1.95, the best-performing Gd0.1Ce0.83Ga0.07O2-δ achieved nearly a 26-fold increase in ionic conductivity and a 66 % reduction in activation energy. The clearance coefficient of Gd0.1Ce0.83Ga0.07O2-δ reached 100.95, while the blocking factor decreased by nearly 73 % compared to Gd0.1Ce0.9O1.95. The incorporation of Ga ions led to a nearly one order of magnitude reduction in the dissipation of oxygen vacancy concentration in the space charge layer, with the potential decreasing from 0.3971V (Gd0.1Ce0.9O1.95) to 0.3117V (Gd0.1Ce0.83Ga0.07O2-δ). Dielectric studies clarified the contribution of the Gd-Ga synergistic effect on interfacial polarization. In terms of single-cell performance, the NiO-GDC| Gd0.1Ce0.83Ga0.07O2-δ|LSCF cell exhibited higher power density and current density, particularly showing a 42.9 % performance improvement at 650 °C compared to NiO-GDC|Gd0.1Ce0.9O1.95|LSCF. Density functional theory calculations indicated that the incorporation of Ga ions effectively suppresses the electronic conductivity of CeO2 and significantly reduces the formation energy, binding energy, and migration barrier of oxygen vacancies. Therefore, Ga-Gd co-doping can be regarded as an effective strategy for enhancing the performance of ceria-based electrolytes in IT-SOFCs.
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