90% Current Efficiency At 0.3% Salinity: Practical Disinfection Of Low Temperature And Low Salt Swimming Pool With RuO ₂ - IrO ₂ Titanium Anode

90% current efficiency at 0.3% salinity: practical disinfection of low-temperature and low salt swimming pools using RuO ₂ - IrO ₂ titanium anodes

The titanium anode plate's core role in swimming-pool disinfection is an in-situ hypochlorous-acid generator. The substrate is commercial-purity titanium TA1 with tensile strength ≥ 240 MPa; in 35 °C, 6 g L⁻¹ NaCl its free-corrosion potential is only –0.09 V vs. SCE, far superior to –0.28 V for 316 L stainless steel, so it tolerates pH 5.5–9.0 and ORP > 800 mV without pitting. The functional coating is a binary RuO₂–IrO₂ oxide (7:3 molar ratio) with rutile structure, 1.2–1.5 µm thick, Ra 0.8–1.0 µm, yielding an active-site density ≥ 2 × 10¹⁴ cm⁻². At 1 kA m⁻² and 1.25 V vs. RHE the chlorine-evolution over-potential is 45 mV, current efficiency 92–94 %, and oxygen side-reaction < 5 %. Free chlorine hydrolyses instantly (pKa 7.54); at 25 °C 83 % is HOCl with E° = +1.49 V, giving > 5-log reduction of Pseudomonas aeruginosa in 30 s. Operation builds a nano IrO₂-rich layer that extends service life to 5 × 10⁴ A h m⁻², equivalent to 1.5–2 swim seasons. Failure mode is coating spallation; the Ti substrate remains intact and can be 100 % re-coated, meeting WEEE ≥ 75 % recyclability.