Effects of chloride and other anions on electrochemical chlorine evolution over self-doped TiO₂ nanotube array

Abstract

Electrochemically reduced TiO₂ nanotube arrays (r-TiO₂ NTA) have emerged as an alternative that can replace the dimensionally stable anode (DSA®) due to comparable performance for chlorine evolution reaction (ClER). However, previous studies have reported applications of r-TiO₂ NTA for ClER only under limited conditions (concentrated NaCl solution without other anions). Thus, the potential of r-TiO₂ NTA for CIER has not yet been fully demonstrated. Therefore, this study focused on investigating ClER of r-TiO₂ NTA under various parameters such chloride concentration (5–1,000 mM) and the presence of other anions (i.e., SO ²⁻₄ , HPO ²⁻₄ , and CO ²⁻₃ ). The results suggest that, at low chloride concentration (5–50 mM NaCl), the r-TiO₂ NTA exhibited higher performance for CIER (production rate of 3.35–9.82 mg l⁻¹ min⁻¹, current efficiency of 14.43–42.04%, energy consumption of 69.24–11.02 Wh g(Cl₂)⁻¹) than RuO₂ (2.55–7.88 mg l⁻¹ min⁻¹, 11.07–33.85% and 77.29–6.84 Wh g(Cl₂)⁻¹, respectively). Additionally, other anions did not affect the ClER of r-TiO₂ NTA more than RuO₂. These can be explained by the indirect pathway of ClER in r-TiO₂ NTA while the direct pathway of RuO₂ was negatively affected by dilute chloride and other anions.