Zn doping effects on oxygen reduction kinetics of PrBa_0.5Ca_0.5Fe₂O_5+δ double perovskite cathode for...

In this study, a series of Zn-doped double perovskite oxides, PrBa_0.5Ca_0.5Fe_2-xZn_xO_5+δ (PBCFZ_x, x = 0-0.20), were synthesized by a sol-gel method and systematically evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Owing to its fully filled 3d¹⁰ electronic configuration, Zn²⁺ incorporation disrupts the Fe-O-Fe superexchange pathway, thereby shifting the dominant charge transport mechanism from long-range electron hopping to localized small-polaron conduction. This modification suppresses surface overoxidation and premature passivation, enhances interfacial charge transfer kinetics at the electrode/gas interface, and significantly reduces the overall charge transfer resistance within the electrochemical system. Electrochemical impedance spectroscopy shows that the optimized composition, PBCFZ_0.10, exhibits a low area-specific resistance of 0.13 Ω cm² at 800 °C, representing a 54% reduction compared with undoped PBCF. An anode-supported single cell employing a PBCFZ_0.10 cathode delivers a peak power density of 673.58 mW cm^-2 at 750 °C, which is 69% higher than that of the pristine PBCF cathode. Density functional theory (DFT) calculations indicate that the incorporation of zinc ions (Zn²⁺) can coordinate and regulate the carrier concentration and spatial distribution through charge compensation-induced oxygen vacancies, thereby simultaneously enhancing the kinetics of oxygen reduction reaction (ORR) and interface charge transport, and effectively reducing the activation energy barrier for oxygen ion migration. In addition, PBCFZ_0.10 shows good chemical compatibility with the Sm_0.2Ce_0.8O_2-δ (SDC) electrolyte and a suitable thermal expansion coefficient of 16.63 × 10^-6 K^-1. These results demonstrate that Zn doping is an effective strategy for developing high-performance iron-based double perovskite cathodes for IT-SOFCs.