Regulating the transition-metal d-band center and metal-oxygen orbital alignment represents a potentially useful approach to improve cathodic oxygen reduction reaction (ORR) kinetics in protonic ceramic fuel cells (PCFCs). Herein, K₂NiF₄-type La_0.5Sr_1.5MnO_4+δ (LSMO) and Fe-based La_0.5Sr_1.5FeO_4+δ (LSFO) cathodes were investigated to clarify how electronic-structure regulation affects oxygen-defect chemistry, oxygen/proton transport, and proton-involved ORR activity. Density functional theory (DFT) calculations reveal that the work-function difference between LSFO and LSMO is negligible, whereas LSFO possesses a more favorable Fe 3d-O 2p energy alignment. This electronic configuration lowers the energetic cost of oxygen-vacancy formation, improves hydration-related proton incorporation, reduces the proton-hopping barrier, and decreases the free-energy barrier for key ORR intermediates. Experimentally, LSFO exhibits enriched oxygen-vacancy-related surface oxygen species, much higher electronic conductivity, and accelerated oxygen/proton surface exchange and diffusion. P_O2/P_H2O-dependent electrochemical impedance spectra further confirm that LSFO promotes multiple p-ORR sub-processes, including interfacial charge/proton transfer, oxygen reduction, and surface oxygen transport. Consequently, the optimized LSFO cathode achieves a peak power density of 2.2 W cm^-2 and a polarization resistance of 0.04 Ω cm² at 700 °C, outperforming LSMO and many reported R-P cathodes. Moreover, the LSFO cell exhibits stable operation over 400 h. These results demonstrate that coordinated regulation of the d-band center and d-p orbital alignment is a viable way to design high-performance K₂NiF₄-type PCFC cathodes.

Efforts to improve the performance of protonic ceramic fuel cells (PCFCs) have been hampered by the limited availability of cathode materials with high activity and durability. One potential approach to enhance electrocatalytic performance is by modifying the particle morphology of the cathode, which potentially reforms transport properties and active reaction sites. Herein, the configuration of cathode particles via controllable growth of cubes was used to ameliorate perovskite-related Pr_1.5Ba_1.5Cu₃O₇ (PBC). The PBC particle geometry changes to a cube when the calcination temperature is switched from 900 to 950 °C, exposing the {100} crystal facets on the surface. This gives rise to more surface oxygen vacancies and efficient Cu²⁺–O–Cu³⁺ electron hopping transition paths, favoring high electrocatalytic activity with expeditious oxygen adsorption/activation and facilitating the oxygen reduction reaction (ORR) process. The particle-cubic PBC cathode assembled at 950 °C (PBC-950) exhibited significantly enhanced performance, with a power output of 1982 mW·cm⁻² and a polarization resistance (R_P) of 0.028 Ω·cm² at 700 °C on a PCFC, outperforming other Co-based and Cu-based single-phase cathodes reported in the literature. Overall, the superior power and polarization performance, along with excellent durability over 200 h, suggest that PBC-950 is a promising alternative for PCFC cathodes. This study demonstrates the potential of controlling particle growth to design highly active electrodes with specialized properties, opening new avenues for material design in PCFCs and related electrocatalytic fields.