Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment.

Yang Yang,Ke Sun,Sofia Ya Hsuan Liou,Yuanyue Liu,Jinghua Guo,Hongtao Yu,Li Cheng Kao,Michael R Hoffmann

doi:10.1021/acscatal.7b04340

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.

Highlights

TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution.[1]
Even though bulk CoOx is reported to be unstable for the oxygen evolution reaction (OER) at pH
An increase in current response is observed on both the Blue and Black NTA electrodes at onset potentials of 2.7 and 1.7 V, respectively (Figure 1c)

Summary

■ INTRODUCTION

TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution.[1]. All of the thermally of cobalt onto Black TiO2 NTA (Co-Black NTA) that results in treated NTAs were determined to be in the anatase phase by a lowering of the OER overpotential and increases electrode XRD (Figure S1). Even though bulk CoOx is reported to be unstable for the OER at pH

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES