Sacrificial Doping of Interstitial Lithium Facilitated Undoped Amorphous/Crystalline RuO₂ Toward Boosted Acidic Water Oxidation

Ruthenium (Ru)‐based catalysts offer a cost‐effective alternative for the large‐scale deployment of proton exchange membrane water electrolysis (PEMWE), but suffer from severe degradation under high anodic potential due to strong Ru‐O covalency and undesirable lattice oxygen participation. Herein, a sacrificial doping of interstitial lithium (Li) strategy is developed to engineer an undoped amorphous/crystalline RuO 2 catalyst (undoped a/c RuO 2 ). Such dual‐phase heterostructure optimizes the d‐band center of Ru and weakens the Ru–O covalency, effectively inhibiting the lattice oxygen participation by steering the reaction toward a more favorable and stable oxygen pathway mechanism (OPM). Operando X‐ray absorption spectroscopy analysis demonstrates that the oxidation states of Ru remain stable even after OER test, effectively suppressing the over‐oxidation to higher valence states and mitigating Ru dissolution. As a result, the undoped a/c RuO 2 delivers outstanding OER performance under acidic conditions, requiring only 178 mV overpotential at 10 mA cm −2 . In PEMWE, it only needs a low cell voltage of 1.55 V to reach 1 A cm −2 , and maintains stable operation for 800 h at 0.2 A cm −2 . This work provides a new phase‐engineering paradigm toward designing highly robust Ru‐based catalysts for acidic water electrolysis.