Breaking the Activity-Stability Trade-Off of RuO2-Based Electrocatalysts for Proton Exchange Membrane Water Electrolyzer: Modulation Strategies and Mechanism Elucidation.

Proton exchange membrane water electrolyzer (PEMWE) is a pivotal technology for renewable green hydrogen production, yet its large-scale deployment is limited by expensive and rare Ir-based oxygen evolution reaction (OER) electrocatalysts. RuO2 emerges as a promising Ir-free alternative attributed to relatively high reserves and optimal binding affinity for OER intermediates that overcomes the strong-binding limitations of Ir-based catalysts. However, the applications of RuO2 in PEMWE are severely hindered by the inherent activity-stability trade-off and severe overoxidation/leaching under harsh industrial operation. Against this background, various advanced electronic and geometric modulation approaches have been adopted to simultaneously enhance the activity and stability of RuO2 to push forward its practical applications. In this review, we start with a comprehensive overview of the recently developed strategies for enhancing the activity and stability of RuO2 in PEMWE. Then, the underlying mechanisms of each strategy in breaking the activity-stability trade-off of RuO2-based electrocatalysts are systematically described. Finally, key challenges and forward-looking optimization strategies are proposed. This review will deliver fundamental insights and rational guidelines for designing robust low-cost RuO2-based electrocatalysts toward scalable industrial PEMWE deployment.