Unveiling the Valence-Driven Charge Compensation Mechanism to Direct Phase Engineering in Ru-Based Catalysts for...

Phase engineering is pivotal for optimizing the electronic structure and reaction pathways of electrocatalysts, balancing high-efficiency charge transfer in single-phase structures against synergistic effects in mixed-phase structures. However, the underlying principles governing phase evolution remain poorly understood. Herein, a valence-driven phase engineering paradigm is established that enables deterministic control over Ru-based catalysts. We reveal that phase formation trajectories are intrinsically dictated by charge compensation mechanisms: tetravalent dopants (Hf, Mn, Sn) maintain single-phase RuO₂ via charge neutrality and lattice matching; trivalent dopants (Cr, Fe, Ga) induce a synergistic RuO₂-Ru hetero-phase structure; whereas divalent dopants (Ni, Cu, Zn) trigger oxide phase separation due to severe charge mismatch. As a demonstration, the RuGa mixed-phase catalyst delivers an exceptional overpotential of 180 mV at 10 mA cm^-2 and survives 500 h in acidic media. When integrated into a PEMWE cell, it achieves 1 A cm^-2 at only 1.63 V with robust stability of 100 h at 500 mA cm^-2. This work provides a fundamental framework for rationally designing durable acidic OER catalysts via valence-controlled phase regulation.