Overcoming Kinetic Limitations of Ruddlesden–Popper Cathode via Hollow Nanofiber toward Intermediate-Temperature SOFCs

The electrochemical performance of Nd 0.8 Sr 1.2 CoO 4 ± δ (NSC 214 ) hollow nanofiber cathodes was evaluated using electrochemical impedance spectroscopy (EIS) combined with distribution of relaxation time (DRT) analysis. Compared with the NSC 214 composition investigated in bulk powder form, which represents the intrinsic electrochemical activity of the A 2 BO 4 phase, the hollow nanofiber architecture with a specific surface area of ∼36 m 2 g –1 delivers substantially reduced polarization resistance ( R p ) values of 0.51 and 0.32 Ω cm 2 at 600 and 650 °C, respectively, approximately three times lower than those of the powder electrode. Conventional equivalent circuit modeling (ECM) provides an overall resistance hierarchy, whereas DRT analysis enables frequency-domain deconvolution of the impedance response, revealing significantly reduced resistive contributions in the midfrequency processes and a lower apparent activation energy ( E a ) for the oxygen reduction reaction (ORR) in the nanofiber cathode. The observed performance enhancement is consistent with a vacancy-enriched surface chemistry and increased Co 2+ surface concentration promoted by the high surface area. These features are associated with facilitated oxygen surface exchange and vacancy-mediated transport, resulting in reduced R p and lower apparent activation barriers. It is noted that the DRT peak assignments discussed herein are based on literature analogy; p O 2 -dependent validation experiments were not performed in this study. This work demonstrates that hollow nanofiber architectures represent an effective morphological engineering strategy for developing high-performance oxygen electrodes for intermediate-temperature SOFCs (IT-SOFCs).