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CoOx thin film deposited by CVD as efficient water oxidation catalyst: change of oxidation state in XPS and its correlation to electrochemical activity

Weidler, Natascha and Paulus, Sarina and Schuch, Jona and Klett, Joachim and Hoch, Sascha and Stenner, Patrick and Maljusch, Artjom and Brötz, Joachim and Wittich, Carolin and Kaiser, Bernhard and Jaegermann, Wolfram (2016):
CoOx thin film deposited by CVD as efficient water oxidation catalyst: change of oxidation state in XPS and its correlation to electrochemical activity.
In: Phys. Chem. Chem. Phys., pp. 10708 -10718, 18, ISSN 1463-9076, [Online-Edition: http://dx.doi.org/10.1039/C5CP05691H],
[Article]

Abstract

To reduce energy losses in water electrolysers a fundamental understanding of the water oxidation reaction steps is necessary to design efficient oxygen evolution catalysts. Here we present CoOx/Ti electrocatalytic films deposited by thermal and plasma enhanced chemical vapor deposition (CVD) onto titanium substrates. We report electrochemical (EC), photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. The electrochemical behavior of the samples was correlated with the chemical and electronic structure by recording XPS spectra before and after each electrochemical treatment (conditioning and cyclovoltammetry). The results show that the electrochemical behavior of CoOx/Ti strongly depends on the resulting electronic structure and composition. The thermal deposition leads to the formation of a pure Co(II)Ox which transforms to a mixed Co(II)Co(III)Ox during the OER. This change in oxidation state is coupled with a decrease in overpotential from η = 0.57 V to η = 0.43 V at 5 mA cm−2. Plasma deposition in oxygen leads to a Co(III)-dominated mixed CoOx, that has a lower onset potential as deposited due to a higher Co(III) content in the initial deposited material. After the OER XPS results of the CoOx/Ti indicate a partial formation of hydroxides and oxyhydroxides on the oxide surface. Finally the plasma deposition in air, results in a CoOxOH2 surface, that is able to completely oxidizes during OER to an oxyhydroxide Co(III)OOH. With the in situ formed CoOOH we present a highly active catalyst for the OER (η = 0.34 at 5 mA cm−2; η = 0.37 V at 10 mA cm−2).

Item Type: Article
Erschienen: 2016
Creators: Weidler, Natascha and Paulus, Sarina and Schuch, Jona and Klett, Joachim and Hoch, Sascha and Stenner, Patrick and Maljusch, Artjom and Brötz, Joachim and Wittich, Carolin and Kaiser, Bernhard and Jaegermann, Wolfram
Title: CoOx thin film deposited by CVD as efficient water oxidation catalyst: change of oxidation state in XPS and its correlation to electrochemical activity
Language: English
Abstract:

To reduce energy losses in water electrolysers a fundamental understanding of the water oxidation reaction steps is necessary to design efficient oxygen evolution catalysts. Here we present CoOx/Ti electrocatalytic films deposited by thermal and plasma enhanced chemical vapor deposition (CVD) onto titanium substrates. We report electrochemical (EC), photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. The electrochemical behavior of the samples was correlated with the chemical and electronic structure by recording XPS spectra before and after each electrochemical treatment (conditioning and cyclovoltammetry). The results show that the electrochemical behavior of CoOx/Ti strongly depends on the resulting electronic structure and composition. The thermal deposition leads to the formation of a pure Co(II)Ox which transforms to a mixed Co(II)Co(III)Ox during the OER. This change in oxidation state is coupled with a decrease in overpotential from η = 0.57 V to η = 0.43 V at 5 mA cm−2. Plasma deposition in oxygen leads to a Co(III)-dominated mixed CoOx, that has a lower onset potential as deposited due to a higher Co(III) content in the initial deposited material. After the OER XPS results of the CoOx/Ti indicate a partial formation of hydroxides and oxyhydroxides on the oxide surface. Finally the plasma deposition in air, results in a CoOxOH2 surface, that is able to completely oxidizes during OER to an oxyhydroxide Co(III)OOH. With the in situ formed CoOOH we present a highly active catalyst for the OER (η = 0.34 at 5 mA cm−2; η = 0.37 V at 10 mA cm−2).

Journal or Publication Title: Phys. Chem. Chem. Phys.
Volume: 18
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Surface Science
11 Department of Materials and Earth Sciences > Material Science > Structure Research
Date Deposited: 23 Mar 2016 17:15
Official URL: http://dx.doi.org/10.1039/C5CP05691H
Identification Number: doi:10.1039/C5CP05691H
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