Isovalent A-Site Nd substitution in La-based high-entropy perovskites for enhanced bifunctional oxygen electrocatalysis and rechargeable zinc–air batteries

Rechargeable zinc–air batteries require bifunctional air-cathode catalysts capable of efficiently catalyzing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, La_1-xNd_x (Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2) O₃ (x = 0, 0.1, 0.2, and 0.3) high-entropy perovskites (HEP) were synthesized to examine the influence of isovalent Nd³⁺ substitution at the A site on bifunctional oxygen electrocatalysis. Replacement of La³⁺ with smaller Nd³⁺ preserves the nominal A-site charge while inducing lattice contraction and modifying the surface chemical environment of the multication perovskite. Among the investigated compositions, HEP-Nd-0.3 exhibits the best bifunctional activity, delivering an OER overpotential of 290 mV at 10 mA cm⁻², an ORR half-wave potential of 0.75 V versus RHE, and a bifunctional potential gap of 0.77 V. When used as the air-cathode catalyst in a rechargeable zinc–air battery, HEP-Nd-0.3 achieves a peak power density of 115 mW cm⁻² and stable charge–discharge operation for >340 h. The enhanced performance is associated with Nd-content-dependent variations in lattice structure, surface oxygen chemistry, electrochemically accessible surface area, and charge-transfer characteristics. These results identify isovalent rare-earth A-site substitution as a practical strategy for tuning high-entropy perovskite oxygen electrocatalysts.