Activating Lattice Oxygen Oxidation Mechanism in Asymmetric [IrO6] Octahedra of Ir-Based Oxides Toward Superior Acidic Electrochemical Water Oxidation

The activation of lattice oxygen oxidation mechanism (LOM) will endow iridium-based electrocatalysts with desired acid-available water oxidation activity, compared to the conventional adsorbate evolution mechanism (AEM). However, the inherent symmetric [IrO₆] octahedra of commercial Ir-based catalysts generally thermodynamically favor the AEM pathway contributing to the moderate water oxidation performance. Here, based on typical layered Ca₂IrO₄ (CIO) modeled materials, the d-orbitals electron repulsion strategy is demonstrated, via constructing asymmetrically polarized Ir‒O‒Ru configuration in Ru-CIO, to effectively activate the lattice oxygen participating in water oxidation process for decent oxygen-related electrocatalytic activity. Specifically, a great increase of ≈700-fold and ≈170-fold in mass activity and turnover frequency, respectively, has been realized for the optimal Ru-CIO electrocatalyst in an acid medium relative to the commercial IrO₂ electrocatalysts, where a small overpotential of only 175 mV is required for achieving 10 mA cm_geo^‒2. In situ X-ray fine structure spectroscopies combined with in situ ¹⁸O- isotope-labeled differential electrochemical mass spectrometry analyses reveal that desirable LOM has been boosted by the activated lattice oxygen and the flexible Ir^(3+δ)+ active sites of asymmetric [IrO₆] octahedra, which results in superior OER kinetics for Ir-based oxide catalysts.