Effects of Chloride and Other Anions on Electrochemical Chlorine Evolution over Self-Doped TiO2 Nanotube Array

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 4 2− , HPO 4 2− , and CO 3 2− ). 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.