Selective chlorine evolution reaction using Pt-RuO₂ electrocatalysts in brackish water and seawater at circum-neutral pH and its application to seawater desalination

Precious metal-based mixed metal oxides have been widely used as catalysts for the chlorine evolution reaction (CER). However, a concurrent oxygen evolution reaction (OER) leads to insufficient selectivity for CER at circum-neutral pH. Herein, nanoparticulate Pt-RuO₂ (PRO) is synthesized with various Pt/Ru ratios at sub-boiling temperatures, followed by post-annealing. The synthetic conditions significantly influence the physicochemical properties (crystalline structures, morphologies, surface areas, double-layer capacitance, and charge transfer resistance) and the electrocatalytic activities of CER in NaCl solutions (0.137 and 0.5 M) and seawater (with a salinity of 3.6 g L^–1). Among PRO-x@y samples (where x is the mole fraction of Pt in the mixed Pt and Ru precursor solutions, and y is the annealing temperature [°C]), PRO-0.2@800 and PRO-0.8@500 show remarkable faradaic efficiencies (FEs) for CER (CER-FE). Despite their similar FEs (CER-FEs of approximately 95 % and 99 %, and OER-FEs of 4–6 % and <1 %, for PRO-0.2 and PRO-0.8, respectively), the Pt-rich PRO requires less potential for the same current density (J) and exhibits excellent stability at J = 800 mA cm^–2 over 250 h in seawater at circum-neutral pH. The optimized PRO electrode is further used for seawater desalination and simultaneous production of HClO, achieving FEs of ∼100 %. Finally, various electrochemical analyses are conducted to elucidate the CER mechanism.