Anomalous potential dependence of conducting property in black titania nanotube arrays for electrocatalytic chlorine evolution

Ru- and Ti-based oxide electrocatalysts have been intensively studied for chlorine evolution reactions since their synergistic effect was demonstrated in commercial dimensionally stable anodes. Basically, oxide materials intrinsically possess a semiconducting nature; therefore, tuning conducting properties is important in achieving high electrocatalytic activity. Here, black TiO2 nanotube arrays deposited with RuO2 by pulsed electrodeposition are investigated as a three-dimensional supporting electrode for chlorine and hydrogen evolution. RuO2-loaded black titania achieves high chlorine evolution activity (10 and 100 mA cm−2 at 1.090 and 1.125 V vs. SCE) with a faradaic efficiency of 95.25% while RuO2-loaded titania has no activity, though hydrogen evolution reaction performance is similar. This suggests that the type of titania support affects the conducting property at anodic potentials and chlorine evolution activity. This work provides new insights into the importance of black titania materials in enhancing the electrocatalytic activity of anodic reactions.