Effect of Thermal Treatment on the Electronic Conductivity Properties of Cobalt Spinel Phases Synthesized by Electro-Oxidation in Ternary Alkaline Electrolyte (KOH, LiOH, NaOH)

Douin, Myriam; Guerlou‐Demourgues, Liliane; Ménétrier, Michel; Bekaert, Émilie; Goubault, Lionel; Bernard, Patrick; Delmas, Claude

doi:10.1021/cm801775g

Cited by 20 publications

(32 citation statements)

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“…Generally, the structural flexibility of spinel-type oxides is an asset for the tuning of site occupancies, oxidation states, and dopant contents toward higher catalytic activity. [31][32][33][34][35][36] On the other hand, the comprehensive surface, structural, and morphological characterization of a given spinel-based material quickly turns into a demanding task that requires numerous complementary analytical techniques, especially for complex and mixed-valent compounds. UV/Vis spectroscopic analyses, for example, impressively demonstrate the diver-Abstract: Water oxidation is the "bottleneck" of artificial photosynthesis on the way to clean and sustainable solar fuels production.…”

Section: Introductionmentioning

confidence: 99%

Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies

Liu

Patzke

2014

Chemistry An Asian Journal

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Water oxidation is the "bottleneck" of artificial photosynthesis on the way to clean and sustainable solar fuels production. Although spinel-type Co3 O4 keeps attracting considerable research interest as a robust and low-cost water oxidation catalyst (WOC), full control over its manifold performance parameters remains a preparative and analytical challenge. The present study screens a wide spectrum of influential factors (such as surface area and adsorption processes, morphology, crystallinity, and cobalt oxidation states) with respect to straightforward WOC optimization strategies. Tuning of crystallinity and cobalt valence states emerges as a major guideline for spinel catalyst synthesis, thus adding a key complementary factor to the main design paradigm of surface area maximization. In contrast to the prevailing amorphous characteristics of electrocatalytic WOCs, crystallinity was found to be crucial for photochemical WOC development. The interplay of synthetic history, crystallinity, and cobalt valence states in hydrothermally synthesized Co3 O4 WOCs was investigated with a variety of analytical techniques, including electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and various electron microscopy and spectroscopic techniques. Complementary "top down" and "bottom up" optimization strategies introduce new Co3 O4 WOC design parameters for facile catalyst production.

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Section: Introductionmentioning

confidence: 99%

Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies

Liu

Patzke

2014

Chemistry An Asian Journal

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“…3, together with the diagram of a reference high temperature Co 3 O 4 phase. They are characteristic of pure phases with a spinel type structure (cubic structure, Fd3m space group), 23,25 and exhibit very broad lines, which are typical of nanometric coherent domains. Scherrer formula allows indeed to evaluate coherent domain sizes ranging from 5 to 10 nm.…”

Section: Resultsmentioning

confidence: 99%

“…This behavior could be attributed to the presence of cobalt vacancies (16 d and 8a sites) in the spinel network, as we already pointed out in cobalt spinel phases prepared by electrooxidation. 23,25,26 A more detailed structural analysis of our materials will be published elsewhere.…”

Section: Resultsmentioning

confidence: 99%

“…,25 A detailed characterization of these phases, especially by X ray diffraction, leads to propose formulae such as: H x On the basis of these previous studies and of the chemical analysis results ofTable I, we can reason-Table I. Weight percentages of cobalt, lithium, hydrogen, sodium and potassium; corresponding molar ratio; and average oxidation state of cobalt in the as-prepared spinel materials.…”

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confidence: 99%

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Strategies for Synthesizing Conductive Spinel Cobalt Oxide Nanoparticles for Energy Storage Applications

Shaju

Guerlou‐Demourgues

Godillot

et al. 2012

J. Electrochem. Soc.

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Co 3 O 4 spinel type nanoparticles (5-10 nm) were synthesized by oxidizing precipitation in various basic solutions. The materials prepared in lithium-containing hydroxide solutions exhibit high electronic conductivity (higher than 10 −2 S.cm −1 at room temperature), which can be increased (up to 3 S.cm −1 ) by electrochemical oxidation. This high conductivity is due to the presence of Co 4+ ions in the octahedral framework of the spinel structure, which entails electronic delocalization. In addition to high conductivity, the obtained powder exhibits a high surface area (around 200 m 2 .g −1 ), which should be suitable for applications in electrodes: as conductive additive in the positive electrode of alkaline Ni-MH cells, or directly as electrode material in hybrid C/metal oxide supercapacitors.Co 3 O 4 was intensively studied for its potential applications in numerous fields such as electrochemistry and energy storage, 1-5 catalysis, 6-9 sensors 10,11 or magnetism. 12 A classical synthesis procedure of Co 3 O 4 consists of thermal decomposition of cobaltous salts at high temperature (300 • C-900 • C) under oxidizing conditions. 13,14 But such methods lead often to large crystallites (0.1-1 μm), unsuitable to explore the full range of intrinsic properties. Various synthesis procedures of Co 3 O 4 nanoparticles were reported in the literature: oxidative precipitation from aqueous solutions, 15,16 thermal decomposition of cobalt alkoxides 3 or inorganic precursors. 8,17 Mesoporous Co 3 O 4 was also synthesized by hydrothermal method, 18,19 template removal 9,20,21 or decomposition of cobalt oxalate. 22 We reported recently the preparation and characterization, in our laboratory, of battery-related H x Li y Co 3−δ O 4 original spinel materials, exhibiting high electronic conductivity. 23-26 These materials were synthesized by electrochemical oxidation of CoO in alkaline electrolyte containing the three components: KOH, NaOH, LiOH. They were intended to be used as conductive additives in the positive electrode of Ni-MH batteries. Let us remind that the structure of ideal cubic Co 3 O 4 , which is a normal spinel with the general formula A[B 2 ]O 4 , can be described as a 3 dimensional -[Co 2 O 4 ] framework of Co 3+ ions in edge-sharing octahedral B sites, where Co 2+ ions are located in tetrahedral A sites that share only corners with the octahedra. An overlapping of the cobalt t 2g orbitals across the shared edges of the CoO 6 octahedra occurs. In the case of ideal Co 3 O 4 , the t 2g band is completely filled, due to the electronic configuration of Co 3+ (d 6 LS) ions, leading to a semi-conductor behavior with a very low electronic conductivity (about 10 −5 S.cm −1 at room temperature). The phases that we synthesized in the presence of lithium ions are different from the ideal Co 3 O 4 phase, by the presence of protons, of lithium and of cobalt vacancies within the spinel structure, and of Co 4+ in the octahedral [Co 2 O 4 ] framework. 23 The negative charge resulting from cobalt vacancies is compensated by lithi...

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“…That is the reason why research works are now devoted to new additives, to prevent the instability of the conductive network. The addition of bismuth to the cobalt phases [8] or the use of a conductive H x Li y Co 3−ı O 4 spinel type phase, formed in situ under specific conditions [9][10][11], are solutions proposed in literature.…”

Section: Introductionmentioning

confidence: 99%

Effect of deep discharge on the electrochemical behavior of cobalt oxides and oxyhydroxides used as conductive additives in Ni-MH cells

Douin¹,

Guerlou‐Demourgues²,

Goubault³

et al. 2009

Journal of Power Sources

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Effect of Thermal Treatment on the Electronic Conductivity Properties of Cobalt Spinel Phases Synthesized by Electro-Oxidation in Ternary Alkaline Electrolyte (KOH, LiOH, NaOH)

Cited by 20 publications

References 23 publications

Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies

Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies

Strategies for Synthesizing Conductive Spinel Cobalt Oxide Nanoparticles for Energy Storage Applications

Effect of deep discharge on the electrochemical behavior of cobalt oxides and oxyhydroxides used as conductive additives in Ni-MH cells

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Effect of Thermal Treatment on the Electronic Conductivity Properties of Cobalt Spinel Phases Synthesized by Electro-Oxidation in Ternary Alkaline Electrolyte (KOH, LiOH, NaOH)

Cited by 20 publications

References 23 publications

Visible‐Light‐Driven Water Oxidation with Nanoscale Co3O4: New Optimization Strategies

Visible‐Light‐Driven Water Oxidation with Nanoscale Co3O4: New Optimization Strategies

Strategies for Synthesizing Conductive Spinel Cobalt Oxide Nanoparticles for Energy Storage Applications

Effect of deep discharge on the electrochemical behavior of cobalt oxides and oxyhydroxides used as conductive additives in Ni-MH cells

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Product

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Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies

Visible‐Light‐Driven Water Oxidation with Nanoscale Co₃O₄: New Optimization Strategies