Tailoring electrocatalytic performance for ORR of medium-entropy Ruddlesden–Popper type electrode through rational ionic potential design

The mechanism by which the multicomponent systems in high-entropy perovskites regulate catalytic sites remains unclear, especially how the introduction of A-site elements with different radii influences the B-site catalytic centers. This study designed medium-entropy perovskite oxides, (La 0.2 Pr 0.2 Nd 0.2 Sm 0.2 M 0.2 ) 2 NiO 4 (M = Ca, Sr, Ba), by leveraging the differential ionic potentials of strategically selected alkaline earth metals, with the aim of elucidating how systematic modifications of the local polar environment influence the bonding state of catalytic sites and their electrocatalytic behavior. The differing ionic potentials of the A-site cations (Ca, Sr, Ba) modulate the bond strength and electron cloud overlap of the B-site transition metal‑oxygen bonds. This modulation, primarily through coulombic interactions with the B-site metal ions, induces significant electron transfer and consequently adjusts the energy of the d-band center. This weakened interaction facilitates the generation and migration of active oxygen species by lowering the metal‑oxygen bond strength. Electrochemical results indicate that (La 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Ba 0.2 ) 2 NiO 4 (LPNSBNO) exhibits a low polarization resistance of 0.29 Ω cm 2 at 700 °C. The single cell of LPNSBNO achieved a maximum power density of 0.82 W cm −2 in fuel cell mode. A current density of 0.58 A cm −2 was achieved in electrolyzer mode at 1.3 V and 700 °C. Furthermore, compared to Nd 1.6 Ba 0.4 NiO 4 , the entropy-enhanced LPNSBNO exhibits weaker Ba 2+ surface segregation energy, thereby demonstrating more robust Cr/CO 2 resistance. These results establish LPNSBNO as a catalyst with significant potential for bi-functional applications.