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

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 Co₂TiO₄/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)-Co₂TiO₄/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)-Co₂TiO₄/Ti-prepared by direct RuCl₃ deposition without chelating agents and featuring RuO₂ nanoclusters (NC)-the single-site structure in Ru(SA)-Co₂TiO₄/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)-Co₂TiO₄/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 Ru³⁺/Ru⁴⁺ single-atom Ru within the orthorhombic Co₂TiO₄ phase, accompanied by increased Co^δ+ and oxygen vacancies, promoting Cl^- adsorption and facilitating Cl₂ formation via a positive-valent chlorine intermediate.