Electrochemical and electrical properties of doped CeO₂-ZnO composite for low-temperature solid oxide fuel cell applications

Zinc oxide (ZnO) as a multi-function semiconductor is widely known for photocatalysis and electronic applications but exceptionally new in Solid State Ionics. In this study, a new semiconducting-ionic conductor is reported for solid oxide fuel cells (SOFCs) applications by composing ZnO with an ionic conductor La/Pr co-doped CeO₂ (LCP) in various mass ratios. The prepared composites acting as membranes are sandwiched between two Ni_0.8Co_0.15Al_0.05LiO_2-δ (NCAL) electrodes to construct fuel cells. A remarkable maximum power output of 1055 mW cm⁻² is attained along with a high open circuit voltage (OCV) of 1.04 V at 550 °C by the fuel cell using an optimal composition of 7LCP-3ZnO. The electrical properties of the composites as a function of LCP/ZnO ratio are studied through EIS measurements and polarization curves. It has been found that the composite of 7LCP-3ZnO exhibits a higher ionic conductivity than other composite samples at 475-550 °C, while possessing both high electronic and ionic conduction. Our further investigation also verifies the appreciable protonic conduction in LCP-ZnO, suggesting that the developed composite is a triple O^2-/H⁺/e⁻ conducting material. Additionally, rectification characteristic of the best-performance cell is also measured to interpret the high OCVs and power outputs of LCP-ZnO fuel cells.