Unveiling the Valence‐Driven Charge Compensation Mechanism to Direct Phase Engineering in Ru‐Based Catalysts for Acidic Water Electrolysis

ABSTRACT 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 RuO 2 via charge neutrality and lattice matching; trivalent dopants (Cr, Fe, Ga) induce a synergistic RuO 2 ‐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.