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

Electrochemically reduced TiO 2 nanotube arrays (r-TiO 2 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-TiO 2 NTA for ClER only under limited conditions (concentrated NaCl solution without other anions). Thus, the potential of r-TiO 2 NTA for CIER has not yet been fully demonstrated. Therefore, this study focused on investigating ClER of r-TiO 2 NTA under various parameters such chloride concentration (5–1,000 mM) and the presence of other anions (i.e., SO 4 2− , HPO 4 2− , and CO 3 2− ). The results suggest that, at low chloride concentration (5–50 mM NaCl), the r-TiO 2 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(Cl 2 ) −1 ) than RuO 2 (2.55–7.88 mg l −1 min −1 , 11.07–33.85% and 77.29–6.84 Wh g(Cl 2 ) −1 , respectively). Additionally, other anions did not affect the ClER of r-TiO 2 NTA more than RuO 2 . These can be explained by the indirect pathway of ClER in r-TiO 2 NTA while the direct pathway of RuO 2 was negatively affected by dilute chloride and other anions.