In the solid oxide fuel cell field, heterogeneous ion doping is a common methodology to improve the ionic conductivity of electrolytes, but overwhelming grain boundary resistance is still the main obstacle for low‐temperature applications. According to previous reports, building rapid ion transport at the grain boundary through compositing methods was considered as a proposed design for electrolytes to decrease the grain boundary resistance and obtain high ionic conductivity. Herein, Ce0.9Gd0.1O2 − δ (GDC) is selected as the matrix material and composited with Na2CO3 and NdBa0.5Sr0.5Cu2O5 + δ (NBSCu) to form GDC‐Na2CO3 nanocomposite and GDC‐NBSCu composite. The grain boundary conductivity (σb) is delicately separated from the EIS results, demonstrating that the σb of GDC‐NBSCu and GDC‐Na2CO3 composite are both substantially higher than that of pure GDC. Therefore, the power density maximum of GDC‐NBSCu and GDC‐Na2CO3 electrolyte is 726 mW cm−2 at 600 °C and 797 mW cm−2 at 575 °C, respectively. Variety of characterization reveales that the proton contributes to the enhancement of σb in GDC‐Na2CO3, while the band energy alignment between GDC and NBSCu works as an accelerator to promote the ionic conduction for GDC‐NBSCu.
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