Low-Valent RuIr Oxide With Reversible Valence Dynamics and Robust Framework for Oxygen Evolution Electrocatalysis.

The widespread deployment of proton exchange membrane water electrolyzers for hydrogen production is hindered by a lack of durable and active anode electrocatalysts for the oxygen evolution reaction (OER). Here, we report a class of low-valent RuIr oxide nanocatalysts that simultaneously achieve high OER activity and durability. Through an ethylene glycol-mediated reduction, the conventional RuIr oxide framework with metals in tetravalent oxidation states is transformed into a distorted monoclinic structure in which Ru and Ir are stabilized at reduced valence states below +4. A combination of in situ spectroscopies and isotope-tracing mass spectrometry reveals a dynamic yet structurally robust behavior of the chemically reduced catalyst. During OER, Ru and Ir undergo reversible valence changes and recover after potential relaxation, while the oxide framework remains unchanged and the catalyst follows the adsorbate evolution mechanism. In a PEMWE cell, the optimal catalyst achieves current densities of 1.0 A cm-2 at 1.61 V and 2.0 A cm-2 at 1.74 V, with low degradation rates over 2000 h for each current density, and retains more than 94% of its initial activity after 40 000 dynamic voltage cycles. The low-valent strategy, with dynamic adaptability and structural robustness, offers an efficient design principle for high-performance RuIr-based catalysts.