Dynamically Activating Inert Ti 4+ Sites to Redirect the Oxygen Evolution Pathway Toward Practical PEM Water Electrolysis

ABSTRACT Developing highly active and durable non‐iridium electrocatalysts for the acidic oxygen evolution reaction (OER) is critical for scalable proton exchange membrane water electrolyzers (PEMWE). Here, we report an acid‐dissolution inverse‐doping strategy to synthesize Ti‐doped RuO 2 (Ti‐RuO 2 ) with atomic‐level uniformity. This induces compressive lattice strain and a unique 3d–2p–4d orbital hybridization, dynamically activating traditionally inert Ti 4+ sites into highly active centers for direct water molecule activation while lowering the rate‐determining step barrier. Operando spectroscopy and theoretical calculations reveal a cooperative interaction between Ti and Ru sites via a Ti–O–O–Ru bridged intermediate, shifting the mechanism from the conventional adsorbate evolution mechanism (AEM) to a Ti–Ru dual‐site oxide path mechanism (OPM). Furthermore, activated Ti sites optimize interfacial water structure, accelerating proton transfer and suppressing lattice oxygen oxidation, thereby enhancing the catalyst's stability. Consequently, Ti‐RuO 2 achieves an overpotential of 218 mV at 10 mA cm −2 and operates stably for over 800 h. In a practical PEMWE device, it delivers 3 A cm −2 at 1.787 V, exceeding the US DOE 2026 target, and operates over 400 h at 1 A cm −2 with a minimal voltage degradation. This work introduces a promising non‐iridium catalyst and a general strategy for dynamic dopant activation.