Nanostructured α- and β-cobalt hydroxide thin films |
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| Authors: | Jeffrey RS Brownson Claude Lvy-Clment |
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| Affiliation: | aInstitut de Chimie et Matériaux de Paris-Est, CNRS-Université Paris 12, UMR 7182, 2/8 rue Henri Dunant, 94320 Thiais, France;bDepartment of Energy and Mineral Engineering, The Pennsylvania State University, University Park, PA 16802-5000, USA |
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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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| Keywords: | Cathodic electrodeposition Nitrite Nitrate Cobalt hydroxide Hydrotalcite |
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