Design of La ³⁺ -Engineered Ruddlesden−Popper Manganite: Electrostatic Bandwidth Expansion and Oxygen Vacancy Activation for Robust OER/HER Catalysis

Scalable hydrogen production from seawater electrolysis is constrained by the lack of robust, non-noble catalysts that combine high activity with resistance to chloride-induced degradation. Here, we report a series of La3+-engineered Ruddlesden−Popper manganites synthesized via a mild hydrothermal route, enabling precise control over A-site chemistry and electronic structure. Spectroscopic and electrochemical analyses reveal that La3+ incorporation induces electrostatic modulation that stabilizes Jahn−Teller-active Mn3+, broadens the Mn 3d−O 2p bandwidth, and promotes oxygen-vacancy formation. These effects enhance redox flexibility, accelerate Mn−O charge-transfer kinetics, and activate lattice-oxygen redox pathways. As a result, the La-rich composition exhibits outstanding bifunctional performance in alkaline seawater, requiring overpotentials of 330 mV for oxygen evolution and 306 mV for hydrogen evolution at 100 mA cm−2, and sustaining operation at current densities up to 300 mA cm−2. The catalyst further demonstrates minimal degradation under prolonged operation, indicating strong resistance to chloride corrosion.