Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment
Journal
ACS Catalysis
Journal Volume
8
Journal Issue
5
Pages
4278-4287
Date Issued
2018
Author(s)
Abstract
TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO2 nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO2 nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO4 electrolyte at 10 mA cm-2. Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (Ov) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, Ov, and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO2 anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoOx film on top of Co-Black electrode. The CoOx/Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO2 (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm-2. © 2018 American Chemical Society.
Subjects
cobalt oxide; conductive TiO2 nanotube array; oxygen evolution reaction; oxygen vacancies; wastewater treatment
Other Subjects
Anodes; Chemicals removal (water treatment); Chlorine compounds; Cobalt compounds; Electrochemical oxidation; Electrolysis; Electrolytes; Electron spin resonance spectroscopy; Iridium compounds; Nanotubes; Paramagnetic resonance; Passivation; Potassium hydroxide; Semiconductor doping; Sodium compounds; Titanium dioxide; Wastewater treatment; Water pollution; Water pollution control; X ray absorption spectroscopy; X ray photoelectron spectroscopy; Yarn; Cobalt oxides; Continuous operation; Electrochemical wastewater treatment; Electrolytic oxidation; Electron conductivity; Enhanced conductivity; Oxygen evolution reaction; TiO2 nanotube arrays; Oxygen vacancies
Type
journal article