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Cobalt doped black TiO_2 nanotube array as a stable anode for oxygen evolution and electrochemical wastewater treatment

Yang, Yang and Kao, Li Cheng and Liu, Yuanyue and Sun, Ke and Yu, Hongtao and Guo, Jinghua and Liou, Sofia Ya Hsuan and Hoffmann, Michael R. (2018) Cobalt doped black TiO_2 nanotube array as a stable anode for oxygen evolution and electrochemical wastewater treatment. ACS Catalysis, 8 (5). pp. 4278-4287. ISSN 2155-5435. PMCID PMC5939910. doi:10.1021/acscatal.7b04340.

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TiO_2 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 TiO_2 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-TiO_2 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 (O_v) 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 IrO_2 anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoO_x film on top of Co-Black electrode. The CoO_x/Co-Black composite electrode was found to have a lower OER overpotential (352 mV) compared to a DSA IrO_2 (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).

Item Type:Article
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URLURL TypeDescription CentralArticle Information
Yang, Yang0000-0003-3767-8029
Liu, Yuanyue0000-0002-5880-8649
Sun, Ke0000-0001-8209-364X
Guo, Jinghua0000-0002-8576-2172
Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 2018 American Chemical Society. ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Received: December 18, 2017. Revised: April 9, 2018. Published: April 10, 2018. This research was supported by the Bill and Melinda Gates Foundation (BMGF RTTC Grants OPP1111246 and OPP1149755). We also used the resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. This work benefited from the use of the TEM facility of Applied Physics and Materials Science Department at Caltech. We acknowledge the National Science Foundation for its support of the Caltech EPR Facility via NSF-1531940. We are grateful to Dr. Paul Oyala from Division of Chemistry and Chemical Engineering of Caltech for help with the EPR measurements and data interpretation.
Funding AgencyGrant Number
Bill and Melinda Gates FoundationOPP1111246
Bill and Melinda Gates FoundationOPP1149755
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:conductive TiO2 nanotube array, cobalt oxide, oxygen vacancies, oxygen evolution reaction, wastewater treatment
Issue or Number:5
PubMed Central ID:PMC5939910
Record Number:CaltechAUTHORS:20180411-114229081
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Official Citation:Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment Yang Yang, Li Cheng Kao, Yuanyue Liu, Ke Sun, Hongtao Yu, Jinghua Guo, Sofia Ya Hsuan Liou, and Michael R. Hoffmann ACS Catalysis 2018 8 (5), 4278-4287 DOI: 10.1021/acscatal.7b04340
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85750
Deposited By: George Porter
Deposited On:11 Apr 2018 19:42
Last Modified:15 Nov 2021 20:31

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