Modulating Ru‐O Covalency Enables Suppressed Lattice Oxygen Pathway and Ru Dissolution for Robust Acidic Chlorine Evolution

The chlorine evolution reaction (CER) is central to chlor‐alkali electrolysis, yet Ru‑based anodes often suffer from competitive oxygen evolution and anodic dissolution under acidic potentials. Here, we report 2D ultrathin amorphous Sn‑doped RuO x nanosheets prepared via atomic engineering, in which Ru‐O covalency and the Ru oxidation state are simultaneously modulated. Structural and spectroscopic analyses indicate that Ru centers are stabilized against over‑oxidation, suppressing the formation of volatile RuO 4 or soluble RuO 5 2− . Operando attenuated total reflection surface‐enhanced infrared absorption spectroscopy, combined with 18 O isotope labeling, reveals negligible lattice‑oxygen participation and a preference for direct Cl − adsorption, thereby suppressing oxygen evolution and promoting CER. The optimized Ru‐based catalyst achieves high CER selectivity (∼97%), long‐term stability (>300 h), and mass activity nearly 40 times higher than commercial benchmarks. These results highlight the significant potential of metal‐oxide bond‐covalency modulation as a viable strategy for durable anodic oxidation electrocatalysis.