A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode

A p-type Cu3Ta7O19 semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamic...

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Autores principales:	Zahirul Sohag, Shaun O’Donnell, Lindsay Fuoco, Paul A. Maggard
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	metastability photoelectrode solar energy conversion semiconductor Organic chemistry QD241-441
Acceso en línea:	https://doaj.org/article/534e4364c54b43239c43f22691fc533f
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spelling	oai:doaj.org-article:534e4364c54b43239c43f22691fc533f2021-11-25T18:27:34ZA Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode10.3390/molecules262268301420-3049https://doaj.org/article/534e4364c54b43239c43f22691fc533f2021-11-01T00:00:00Zhttps://www.mdpi.com/1420-3049/26/22/6830https://doaj.org/toc/1420-3049A p-type Cu<sub>3</sub>Ta<sub>7</sub>O<sub>19</sub> semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu<sub>3</sub>Ta<sub>7</sub>O<sub>19</sub> + x/2 O<sub>2</sub> → Cu<sub>(3−x)</sub>Ta<sub>7</sub>O<sub>19</sub> + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm<sup>−2</sup> up to >0.5 mA cm<sup>−2</sup>, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm<sup>−2</sup>) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.Zahirul SohagShaun O’DonnellLindsay FuocoPaul A. MaggardMDPI AGarticlemetastabilityphotoelectrodesolar energy conversionsemiconductorOrganic chemistryQD241-441ENMolecules, Vol 26, Iss 6830, p 6830 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	metastability photoelectrode solar energy conversion semiconductor Organic chemistry QD241-441
spellingShingle	metastability photoelectrode solar energy conversion semiconductor Organic chemistry QD241-441 Zahirul Sohag Shaun O’Donnell Lindsay Fuoco Paul A. Maggard A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
description	A p-type Cu<sub>3</sub>Ta<sub>7</sub>O<sub>19</sub> semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu<sub>3</sub>Ta<sub>7</sub>O<sub>19</sub> + x/2 O<sub>2</sub> → Cu<sub>(3−x)</sub>Ta<sub>7</sub>O<sub>19</sub> + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm<sup>−2</sup> up to >0.5 mA cm<sup>−2</sup>, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm<sup>−2</sup>) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.
format	article
author	Zahirul Sohag Shaun O’Donnell Lindsay Fuoco Paul A. Maggard
author_facet	Zahirul Sohag Shaun O’Donnell Lindsay Fuoco Paul A. Maggard
author_sort	Zahirul Sohag
title	A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
title_short	A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
title_full	A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
title_fullStr	A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
title_full_unstemmed	A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode
title_sort	metastable p-type semiconductor as a defect-tolerant photoelectrode
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/534e4364c54b43239c43f22691fc533f
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A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode

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