Arunkumar Pandiyan1, Aarthi Uthayakumar, Chaesung Lim, Vinothkumar Ganesan, Wonjong Yu, Amit Das, Sanghoon Lee, Mihalis N.Tsamaps, Shobit Omar, Jeong Woo Han, Suresh Babu Krishna Moorthy, Suk Won Cha
The defect association modifies the energy barrier for oxygen ion hopping between the vacancies, which is sensitive to the dopant ionic size in the CeO2-δ. Here, the work focuses on the co-dopant strategy of M0.1Sm0.1Ce0.8O2-δ (M = Yb, Gd, Sm, Nd, La) to study the defect association energy, and its subsequent effect on ionic conduction and power density. The electrolyte material with different co-dopants modifies the lattice parameter and bond length of cation–anion, which changes the defect–dopant interactions. Among the tested dopant, Nd0.1Sm0.1Ce0.8O2-δ exhibits the highest ionic conductivity of 34 mS cm−1 at 550 °C, which is nearly 2.3 times higher than the conventional Sm0.2Ce0.8O2-δ. This experimental observation validates the theoretically proposed concept of the balanced defect–dopant interactions at different sites leading to the reduction in defect association enthalpy. The experimental results were rationalized by calculating the defect association enthalpy for the co-doped system using density functional theory via one-cell method. The cell with Nd0.1Sm0.1Ce0.8O2-δ as an electrolyte shows a peak power density of 466 mW cm−2 at 550 °C, which is twice higher than the cell containing standard Sm0.2Ce0.8O2-δ electrolyte (212 mW cm−2). The results confirm that Nd0.1Sm0.1Ce0.8O2-δ is the potential electrolyte for low temperature SOFC operation.