Nd doping enables efficient and durable manganese-based water oxidation catalysts under acidic conditions.

Mn oxides are attractive non-noble-metal catalysts for the oxygen evolution reaction in proton exchange membrane water electrolyzers, but their performance is limited by unstable Jahn-Teller-active Mn3+ centers and a narrow potential window. Here, we show that Nd doping stabilizes Jahn-Teller-active Mn3+ centers within a mixed-phase Mn oxide catalyst. The catalyst requires an overpotential of 404 mV to reach 100 mA cm-2 and remains stable for more than 1000 h at 200 mA cm-2. A proton exchange membrane water electrolyzer employing this catalyst operates stably for more than 600 h at 100 mA cm-2. In situ Raman and X-ray spectroscopy, together with isotope-labeling experiments, support an oxide path mechanism and suppressed Mn overoxidation and dissolution. Phase-enriched reference experiments and density functional theory calculations show that Nd-doped α-Mn2O3 favors the oxide path mechanism through structural Mn3+ motifs, whereas β/R-MnO2-rich domains provide structural robustness. Nd-induced 4f-2p-3 d orbital coupling enhances Mn-O covalency and stabilizes Mn3+ centers, thereby improving the activity-stability balance of Mn-based acidic oxygen evolution catalysts.