Nanostructured α- and β-cobalt hydroxide thin films

Jeffrey R.S. Brownson; Claude Lévy-Clément

doi:10.1016/j.electacta.2009.06.034

Nanostructured α- and β-cobalt hydroxide thin films

Jeffrey R.S. Brownson, Claude Lévy-Clément

Research output: Contribution to journal › Article › peer-review

47 Scopus citations

Abstract

A new perspective in the use of electrochemical methods to deposit cobalt hydroxide thin films is presented. Ordered arrays of α-Co(OH)₂ (hydrotalcite-like (Co-HT)) and β-Co(OH)₂ nanoparticles were synthesized on transparent conductive oxide (TCO) substrates by localized cathodic electrogeneration of hydroxyl via the reduction of NO₂^- (or NO₃^-) ion precursors in solution containing Co²⁺ in very low concentration. The thin films, analyzed by X-ray diffraction and scanning electron microscopy were found to be composed of vertically oriented platelets with the crystallographic c-axis parallel to the substrate surface. Turbostratic disorder was not observed in the films. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated distinct variation between the Co-HT structures. Films deposited at 60 °C using a nitrite precursor generated uniform, vibrant-green mixed-valence Co-HT (Co²⁺/Co³⁺). Nitrate precursors yielded a "hydroxyl-deficient" Co-HT (Co²⁺ only). Films deposited at 95 °C in nitrate solution yielded β-Co(OH)₂. The films obtained in presence of nitrite were thicker than those obtained in nitrate. They were formed of β-Co(OH)₂ and contained traces of Co-HT.

Original language	English (US)
Pages (from-to)	6637-6644
Number of pages	8
Journal	Electrochimica Acta
Volume	54
Issue number	26
DOIs	https://doi.org/10.1016/j.electacta.2009.06.034
State	Published - Nov 1 2009

All Science Journal Classification (ASJC) codes

General Chemical Engineering
Electrochemistry

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10.1016/j.electacta.2009.06.034

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abstract = "A new perspective in the use of electrochemical methods to deposit cobalt hydroxide thin films is presented. Ordered arrays of α-Co(OH)2 (hydrotalcite-like (Co-HT)) and β-Co(OH)2 nanoparticles were synthesized on transparent conductive oxide (TCO) substrates by localized cathodic electrogeneration of hydroxyl via the reduction of NO2- (or NO3-) ion precursors in solution containing Co2+ in very low concentration. The thin films, analyzed by X-ray diffraction and scanning electron microscopy were found to be composed of vertically oriented platelets with the crystallographic c-axis parallel to the substrate surface. Turbostratic disorder was not observed in the films. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated distinct variation between the Co-HT structures. Films deposited at 60 °C using a nitrite precursor generated uniform, vibrant-green mixed-valence Co-HT (Co2+/Co3+). Nitrate precursors yielded a {"}hydroxyl-deficient{"} Co-HT (Co2+ only). Films deposited at 95 °C in nitrate solution yielded β-Co(OH)2. The films obtained in presence of nitrite were thicker than those obtained in nitrate. They were formed of β-Co(OH)2 and contained traces of Co-HT.",

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AB - A new perspective in the use of electrochemical methods to deposit cobalt hydroxide thin films is presented. Ordered arrays of α-Co(OH)2 (hydrotalcite-like (Co-HT)) and β-Co(OH)2 nanoparticles were synthesized on transparent conductive oxide (TCO) substrates by localized cathodic electrogeneration of hydroxyl via the reduction of NO2- (or NO3-) ion precursors in solution containing Co2+ in very low concentration. The thin films, analyzed by X-ray diffraction and scanning electron microscopy were found to be composed of vertically oriented platelets with the crystallographic c-axis parallel to the substrate surface. Turbostratic disorder was not observed in the films. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated distinct variation between the Co-HT structures. Films deposited at 60 °C using a nitrite precursor generated uniform, vibrant-green mixed-valence Co-HT (Co2+/Co3+). Nitrate precursors yielded a "hydroxyl-deficient" Co-HT (Co2+ only). Films deposited at 95 °C in nitrate solution yielded β-Co(OH)2. The films obtained in presence of nitrite were thicker than those obtained in nitrate. They were formed of β-Co(OH)2 and contained traces of Co-HT.

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Nanostructured α- and β-cobalt hydroxide thin films

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