High Oxygen Reduction Reaction Activity (Sm_0.6Sr_0.4)_n+1(Ni_0.6Fe_0.4)_nO_3n+1 (n = 1, 2, 3) Cathode with a...

The slow reaction kinetics of the oxygen reduction reaction (ORR) is one of the important challenges facing the development of a cathode in low-temperature solid oxide fuel cells (LT-SOFCs). Herein, we developed the (Sm_0.6Sr_0.4)_n+1(Ni_0.6Fe_0.4)_nO_3n+1 [n-SSNF (n = 1, 2, 3)] cathode with a Ruddlesden-Popper (R-P) structure to investigate its oxygen ion conduction mechanism and cathodic ORR activity. Consequently, the cell device of the n-SSNF (n = 3) cathode accomplished an impressive peak power density of 658 mW·cm^-2. Simultaneously, the device also delivered better low-temperature characteristics and can still operate at 400 °C with a maximum power density of 298 mW·cm^-2. The excellent performance is mainly attributed to the higher cathodic ORR activity, which benefits from the unique R-P structure with the AO rock salt layer and perovskite layer. The AO rock salt layer possess a large number of interstitial oxygen ions, while the perovskite layer can offer a certain amount of oxygen vacancy, which provides a fast channel for oxygen ion transport. Additionally, it exhibits a reduced R_p as low as 0.41 Ω·cm² and has a smaller activation energy (0.31 eV) and bandgap (0.92 eV). The analysis results of time-domain distribution of relaxation times and frequency-domain electrochemical impedance spectroscopy are consistent. These findings open up directions for the design of high-order R-P-structured cathodes for LT-SOFCs.