Dynamically Activating Inert Ti⁴⁺ Sites to Redirect the Oxygen Evolution Pathway Toward Practical PEM Water...

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 RuO₂ (Ti-RuO₂) with atomic-level uniformity. This induces compressive lattice strain and a unique 3d-2p-4d orbital hybridization, dynamically activating traditionally inert Ti⁴⁺ 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-RuO₂ 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.