Superior Oxide Ion Conductivity of Novel Acceptor Doped Cerium Oxide Electrolytes for Intermediate-Temperature Solid Oxide Fuel Cell Applications

Novel compositions of Nd3+ and Dy3+ codoped cerium oxide according to the system of Ce0.8Ndx-yDyyO2-{x-y/2+y} (x = 0.2; y = 0.04, 0.08, 0.1) have been synthesized by a simple sol gel method and studied as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Thermal, microstructural, optical, and electrical properties have been enhanced to different extents by the addition of Nd3+ and Dy3+ ions in cerium lattice, in particularly Dy3+ ions because of their low ionic radius mismatch. Thermogravimetric/differential scanning calorimetric (TG/DSC) analysis exhibited a small weight loss and high thermal stability in the intermediate temperature range (400-800 degrees C). The addition of Dy3+ ions stabilized the cubic fluorite structure, which is confirmed from X-ray diffraction (XRD) studies. Lattice parameter expansion and contraction have been observed on account of their ionic radii trend. The formation of cubic fluorite structure has been confirmed by high-resolution transmission electron microscopy (HRTEM) along with XRD studies. Addition of Dy3+ ions acts as an oxygen vacancy generator that increases the oxygen vacancy concentration and efficient conversion of Ce4+ to Ce3+, which are affirmed with optical studies. Complex impedance analysis was performed at the temperature range from 300 to 600 degrees C in air atmosphere. Compositions of the system Ce0.8Ndx-yDyyO2-{x-y/2+y} (x = 0.2; y = 0.04, 0.08, 0.1) offer competitive oxide ion conductivities in the intermediate temperature range. Ce0.8Nd0.1Dy0.1O1.85 has been found to be an optimum composition with superior oxide ion conductivity of 2.2 X 10(-2) S/cm at 600 degrees C and activation energy of 0.83 eV. Oxide ion conductivity is largely enhanced by the introduction of Dy3+ at intermediate temperature due to the low ionic radius mismatch, concentration of surface oxygen vacancies, and stabilization of cubic fluorite structure. Hence, these results suggest that the composition of Ce0.8Nd0.1Dy0.1O1.85 can be a potential electrolyte for IT-SOFC applications.