Synergistic modulation of Ru oxidation state and oxygen vacancies in Hf x Ru 1− x O 2 for efficient acidic water electrolysis

Proton exchange membrane water electrolysis (PEMWE) is a key technology for sustainable hydrogen production; however, its efficiency is limited by the sluggish kinetics and high overpotential of the anodic oxygen evolution reaction (OER). Although RuO2 offers a cost-effective alternative to scarce IrO2-based catalysts, its application is impeded by a fundamental trade-off between activity and stability under acidic conditions. Herein, we incorporate Hafnium (Hf) into the RuO2 lattice to modulate the Ru oxidation state and oxygen vacancy concentration. The introduction of Hf suppresses Ru overoxidation, while controlled generation of oxygen vacancies minimizes lattice oxygen participation. The optimized Hf0.1Ru0.9O2 catalyst exhibits a low overpotential of 187 mV at 10 mA cm-2 and outstanding durability, maintaining performance for 1500 hours in 0.5 M H2SO4. Notably, a practical PEMWE device employing this catalyst achieves stable operation for over 600 hours at 500 mA cm-2. A combination of in-situ differential electrochemical mass spectrometry (DEMS) and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveal that Hf0.1Ru0.9O2 facilitates oxygen evolution primarily through a multiple-pathway mechanism dominated by the adsorbate evolution mechanism (AEM) and the oxide pathway mechanism (OPM), with effectively suppressed lattice oxygen-mediated mechanism (LOM). These findings establish a new design principle for the development of durable acidic OER electrocatalysts.