Chlorine, a key industrial chemical, is primarily produced through the chlor-alkali process using mixed-metal oxides (MMOs) like dimensionally stable anode (DSA). These anodes face challenges of high overpotential and poor selectivity due to competing oxygen evolution reaction (OER) pathways. This work presents a Zn-doped, defect-engineered RuTiSnZnO_x catalyst on Ti foam to address these issues. The introduction of low-valence Zn creates lattice defects and induces a charge-deficient state at Ru sites. Critically, in-situ electrochemical Raman spectroscopy revealed that this Zn doping facilitates a decisive shift in the key reaction intermediate from Ru-O-Cl to Ru-Cl. This change in the intermediate species directly suppresses the competing OER pathway, thereby enhancing chlorine evolution reaction (CER) selectivity. The catalyst achieves a remarkably low overpotential of 45 mV at 10 mA·cm^–2 and exhibits excellent stability with only 13 mV decay after 1000 hours of operation at 100 mA·cm^–2. Density functional theory (DFT) calculations further demonstrate that Zn incorporation optimizes the electronic structure by shifting the Ru d-band center closer to the Fermi level. This study elucidates how defect engineering through doping can selectively modulate reaction intermediates, providing a new strategy for developing high-performance, cost-effective CER electrocatalysts.

The composition and evolution of interfacial species play a key role during electrocatalytic process. Unveiling the structural evolution and intermediate during catalytic process by in situ characterization can shed new light on the electrocatalytic reaction mechanism and develop highly efficient catalyst. However, directly probing the interfacial species is extremely difficult for most spectroscopic techniques due to complicated interfacial environment and ultra-low surface concentration. Herein, electrochemical core–shell nanoparticle enhanced Raman spectroscopy is utilized to probe the composition and evolution processes of interfacial species on Au@Pt, Au@Co, and Au@PtCo core–shell nanoparticle surfaces. The spectral evidences of interfacial intermediates including hydroxide radical (OH*), superoxide ion (O₂⁻), as well as metal oxide species are directly captured by in situ Raman spectroscopy, which are further confirmed by the both isotopic experiment and density functional theory calculation. These results provide a mechanistic guideline for the rational design of highly efficient electrocatalysts.