Dynamic Structural Self-Optimization in Mn and Ta Codoped RuO₂ for Efficient and Long-Term Acidic Water Oxidation

The instability of ruthenium-based catalysts during the acidic oxygen evolution reaction (OER) remains an obstacle to their practical implementation. In this work, we explore the dynamic self-optimization process (e.g., depletion, migration, and self-healing) of oxygen species in a Mn and Ta codoped RuO₂ catalyst (i.e., MTRO), which acts as a model catalyst for stabilizing the active site during the acidic OER. By integrating tetramethylammonium cation (TMA⁺) chemical probes specific to deprotonated surface oxygen species with differential electrochemical mass spectrometry analysis, we tracked oxygen behavior, revealing that the reaction mechanism shifts from an initial lattice oxygen mechanism (LOM) to a subsequent adsorbate evolution mechanism (AEM). Analysis of the oxygen diffusion coefficient (e.g., D_O) during the LOM pathway indicates that oxygen transportation drives reconstruction of the catalysts, while only moderate transportation could result in a structurally stable catalyst with a constant Ru-O coordination number and an optimal balance between high activity and durability: After codoping Mn and Ta into the RuO₂, the D_O reaches 1.40 × 10^-15 cm² s^-1, which is 1/9 that of undoped RuO₂, ∼25 times that of Mn-doped RuO₂ (MRO). The optimized MTRO catalyst exhibits a low overpotential of 215 mV at 10 mA cm^-2 and operates stably for over 1200 h in 0.5 M H₂SO₄, as well as 600 h of continuous operation in a proton exchange membrane electrolyzer at 0.5 A cm^-2. This work elucidates that the "real" working OER catalysts based on RuO₂ can be of a defective low-coordination structure (in contrast to perfect crystals) with moderate oxygen diffusion efficiency, formed through in situ self-optimization that simultaneously modulates the catalytic reaction pathway.