Unveiling the role of crystallinity of RuO2 catalysts for regulating the acidic oxygen evolution reaction

The intrinsic role of crystallinity in regulating the acidic oxygen evolution reaction (OER) on RuO2 remains elusive due to the synthetic challenge of decoupling structural order from compositional variations. Here, we develop an oxygen-partial-pressure-controlled pyrolysis strategy to achieve graded crystallinity in pure RuO2 nanocatalysts, establishing a pristine model to elucidate this structure-function relationship. We reveal that amorphous RuO2 features disordered dangling oxygen that readily undergoes protonation, triggering a rapid but degradative lattice oxygen-mediated mechanism (LOM) with an ultralow overpotential of 154 mV at 10 mA cm−2. Conversely, increasing crystallinity stabilizes the RuO6 framework, suppressing protonation and shifting the pathway toward the stable adsorbate evolution mechanism (AEM). Crucially, highly crystalline RuO2 demands excessive cell voltages (1.72 V at 1.0 A cm−2) in proton exchange membrane electrolyzers, paradoxically accelerating oxidative etching. This work uncovers a crystallinity-driven LOM-to-AEM transition, identifying intermediate crystallinity as a practical strategy for balancing activity and stability.