Boosting selective chlorine evolution reaction: Impact of Ag doping in RuO₂ electrocatalysts

The chlor-alkali process is critical to the modern chemical industry because of the wide utilization of chlorine gas (Cl₂). More than 95 % of global Cl₂ production relies on electrocatalytic chlorine evolution reaction (CER) through chlor-alkali electrolysis. The RuO₂ electrocatalyst serves as the main active component widely used in commercial applications. However, oxygen evolution reaction (OER) generally competes with CER electrocatalysts at RuO₂ electrocatalyst owing to the intrinsically scaling reaction energy barrier of *OCl and *OOH intermediates, leading to decreased CER selectivity, high energy consumption, and increased cost. Here, the effect of Ag doping on selective CER over RuO₂ electrocatalysts prepared by a sol-gel method has been systematically studied. We found that Ag-doping can effectively improve the Faradaic efficiency of RuO₂ electrocatalyst for CER. Furthermore, the improved CER selectivity of Ag-doped RuO₂ electrocatalysts is highly dependent on the Ag-doping concentration. The optimized Ag_0.15Ru_0.85O₂ electrocatalyst displays an overpotential of 105 mV along with a selectivity of 84.64 ± 1.84 % in 5.0 M NaCl electrolyte (pH = 2.0 ± 0.05), significantly outperforming undoped one (142 mV, 72.75 ± 1.52 %). Our experiments and density functional theory (DFT) calculations show electron transfer from Ag⁺ to Ru⁴⁺ suppresses *OOH intermediates desorption on Ag-doped RuO₂, enabling improved CER selectivity. Such designs of Ag-doped RuO₂ electrocatalysts are expected to be favorable for practical chlor-alkali applications.