Since colossal ionic conductivity was detected in the planar heterostructures consisting of fluorite and perovskite, heterostructures have drawn great research interest as potential electrolytes for solid oxide fuel cells (SOFCs). However, so far, the practical uses of such promising material have failed to materialize in SOFCs due to the short circuit risk caused by SrTiO3. In this study, a series of fluorite/perovskite heterostructures made of Sm-doped CeO2 and SrTiO3 (SDC–STO) are developed in a new bulk-heterostructure form and evaluated as electrolytes. The prepared cells exhibit a peak power density of 892 mW cm−2 along with open circuit voltage of 1.1 V at 550 °C for the optimal composition of 4SDC–6STO. Further electrical studies reveal a high ionic conductivity of 0.05–0.14 S cm−1 at 450–550 °C, which shows remarkable enhancement compared to that of simplex SDC. Via AC impedance analysis, it has been shown that the small grain-boundary and electrode polarization resistances play the major roles in resulting in the superior performance. Furthermore, a Schottky junction effect is proposed by considering the work functions and electronic affinities to interpret the avoidance of short circuit in the SDC–STO cell. Our findings thus indicate a new insight to design electrolytes for low-temperature SOFCs.

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Recently, appreciable ionic conduction has been frequently observed in multifunctional semiconductors, pointing out an unconventional way to develop electrolytes for solid oxide fuel cells (SOFCs). Among them, ZnO and Li-doped ZnO (LZO) have shown great potential. In this study, to further improve the electrolyte capability of LZO, a typical ionic conductor Sm0.2Ce0.8O1.9 (SDC) is introduced to form semiconductor-ionic composites with LZO. The designed LZO-SDC composites with various mass ratios are successfully demonstrated in SOFCs at low operating temperatures, exhibiting a peak power density of 713 mW cm−2 and high open circuit voltages (OCVs) of 1.04 V at 550 °C by the best-performing sample 5LZO-5SDC, which is superior to that of simplex LZO electrolyte SOFC. Our electrochemical and electrical analysis reveals that the composite samples have attained enhanced ionic conduction as compared to pure LZO and SDC, reaching a remarkable ionic conductivity of 0.16 S cm−1 at 550 °C, and shows hybrid H+/O2− conducting capability with predominant H+ conduction. Further investigation in terms of interface inspection manifests that oxygen vacancies are enriched at the hetero-interface between LZO and SDC, which gives rise to the high ionic conductivity of 5LZO-5SDC. Our study thus suggests the tremendous potentials of semiconductor ionic materials and indicates an effective way to develop fast ionic transport in electrolytes for low-temperature SOFCs.