Single‐Atom Ruthenium Sites on Cobalt‐Titanium Surfaces for Efficient and Selective Chloride Electrolysis

ABSTRACT The development of efficient, stable, cost‐effective catalysts for seawater electrolysis is crucial to achieving carbon neutrality and sustainability. Isolated ruthenium single‐atom sites in Ru–O coordination environments are incorporated onto Co ₂ TiO ₄ /Ti supports via an electrostatic approach using Ru–ethylenediaminetetraacetic acid (EDTA) complexes, enabling atomic‐Ru dispersion through interactions between [Ru(EDTA)] ⁻ and metal hydroxide precursors. The resulting Ru(SA)–Co ₂ TiO ₄ /Ti catalyst, with an ultra‐low Ru loading of 0.08 mg cm ^{− 2} (<0.1%), achieves an overpotential of 26.2 mV at 10 mA cm ^{− 2} , a Tafel slope of 39.2 mV dec ^{− 1} , and 87% selectivity toward active chlorine in seawater‐relevant sodium chloride solutions, outperforming state‐of‐the‐art CER systems while using less Ru. Compared to Ru(NC)–Co ₂ TiO ₄ /Ti—prepared by direct RuCl ₃ deposition without chelating agents and featuring RuO ₂ nanoclusters (NC)—the single‐site structure in Ru(SA)–Co ₂ TiO ₄ /Ti shows significantly improved atomic utilization and durability. Electrochemical analysis indicates that both catalysts share a rate‐determining second electron transfer step, yet Ru(SA)–Co ₂ TiO ₄ /Ti exhibits proton‐independent CER kinetics across pH 4.5–9. Structural characterization and X‐ray absorption spectroscopy (XANES and EXAFS) confirm the presence of oxygen‐coordinated, mixed‐valence Ru ³⁺ /Ru ⁴⁺ single‐atom Ru within the orthorhombic Co ₂ TiO ₄ phase, accompanied by increased Co ^δ+ and oxygen vacancies, promoting Cl ⁻ adsorption and facilitating Cl ₂ formation via a positive‐valent chlorine intermediate.