Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Review on recent progress of nanostructured anode materials for Li-ion batteries

Cobalt oxide nanoparticles can carry out overall water splitting with a solar-to-hydrogen efficiency of around 5%.

Efficient solar water-splitting using a nanocrystalline CoO photocatalyst

Photocatalytic water splitting by solar light has received tremendous attention for the production of clean and renewable hydrogen energy from water. Some challenges still remain in improving the solar-to-hydrogen energy conversion efficiency, such as utilizing longer-wavelength photons and enhancing the photocatalytic activity and stability of H2 production over semiconducting materials. Dye sensitization, as a successful strategy for extending the spectral responsive region (even to near-IR light) of wide bandgap semiconductors for H2 production, was developed more than 30 years ago, but it still lacks the corresponding specialized review. This review emphasizes especially the fundamental aspects and the research advances in heterogeneous dye-sensitized semiconductor suspension systems for visible (and even near-IR) light responsive photocatalytic H2 production, and the commonly used dyes, semiconductors, co-catalysts and electron donors are systematically discussed. Also, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest in the field of solar fuel conversion.

Recent advances in dye-sensitized semiconductor systems for photocatalytic hydrogen production

To advance current Li rechargeable batteries further, tremendous emphasis has been made on the development of anode materials with higher capacities than the widely commercialized graphite. Some of these anode materials exhibit capacities above the theoretical value predicted based on conventional mechanisms of Li storage, namely insertion, alloying, and conversion. In addition, in contrast to conventional observations of loss upon cycling, the capacity has been found to increase during repeated cycling in a significant number of cases. As the internal environment in the battery is very complicated and continuously changing, these abnormal charge storage behaviors are caused by diverse reactions. In this review, we will introduce our current understanding of reported reactions accounting for the extra capacity. It includes formation/decomposition of electrolyte-derived surface layer, the possibility of additional charge storage at sharp interfaces between electronic and ionic sinks, redox reactions of Li-containing species, unconventional activity of structural defects, and metallic-cluster like Li storage. We will also discuss how the changes in the anode can induce capacity increase upon cycling. With this knowledge, new insights into possible strategies to effectively and sustainably utilize these abnormal charge storage mechanisms to produce vertical leaps in performance of anode materials will be laid out.

Exploring Anomalous Charge Storage in Anode Materials for Next-Generation Li Rechargeable Batteries.

The design and assembly of suitable nanosystems are key issues in the development of smaller and more efficient lithium batteries. To this regard, cobalt oxides possess very favorable properties for use as negative electrode materials. In this work, we describe a convenient synthesis route to cobalt oxide nanomaterials (both single- and mixed-phase CoO and Co3O4) supported on Ti. The systems are grown by chemical vapor deposition starting from an innovative second-generation molecular source, Co(hfa)2·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, TMEDA = N,N,N′,N′-tetramethylethylenediamine). Controlled variations of the substrate temperature and O2 pressure in the reaction atmosphere enabled tailoring both the phase composition and the system morphology. The electrochemical properties of the obtained nanosystems were evaluated by galvanostatic measurements and impedance spectroscopy. The results showed excellent cycling performances and very high specific capacity values, offering attractive pe...

Cobalt Oxide Nanomaterials by Vapor-Phase Synthesis for Fast and Reversible Lithium Storage

Cobalt oxide nanostructures are deposited by Chemical Vapor Deposition (CVD) on Si(100) substrates at temperatures between 300 and 550 °C, using for the first time a novel Co(II) adduct as molecular precursor [Co(hfa)2·TMEDA; hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, TMEDA = N,N,N′,N′-tetramethylethylenediamine]. The preparation is conducted either under dry (O2) or wet (O2 + H2O) oxygen atmospheres, at total pressures of 3.0 or 10.0 mbar. The obtained results evidence that, upon dry O2 at 10.0 mbar, the initial nucleation of CoO occurs, followed by its progressive oxidation to Co3O4 during the subsequent growth stages. In a different way, cobalt monoxide can be selectively obtained at 3.0 mbar. In all cases, water vapor acts as an oxidant towards cobalt, favoring the formation of Co3O4 phases with a more pronounced {111} and {110}-type faceting. Structural, compositional and morphological characterization evidences the possibility of obtaining high purity CoO/Co3O4 systems with tailored morphological features, from films to columnar nanostructures, thus highlighting the potential and versatility of the proposed synthetic strategy.

http://ematweb.cmi.ua.ac.be/emat/pdf/1644.pdf

Controlled vapor-phase synthesis of cobalt oxide nanomaterials with tuned composition and spatial organization

Al2O3-supported Co3O4 nanosystems were grown by a Chemical Vapor Deposition route under O2 + H2O atmospheres at 500 degrees C. Subsequently, the preparation of Au/Co3O4 composites was attained by Radio Frequency-Sputtering of gold onto the previous Co3O4 nanodeposits. Important data on the system structure, morphology and chemical composition were obtained by the combined use of complementary techniques, namely Glancing Incidence X-ray Diffraction, Field Emission-Scanning Electron Microscopy, Atomic Force Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry. Finally, the gas sensing properties of the synthesized systems were probed in the detection of ethanol and hydrogen. The obtained results revealed significant responses already at moderate temperatures, which could be further enhanced by Co3O4 functionalization with Au nanoparticles.

Andrea Pozza

Papers

Cobalt Oxide Nanomaterials by Vapor-Phase Synthesis for Fast and Reversible Lithium Storage

Controlled vapor-phase synthesis of cobalt oxide nanomaterials with tuned composition and spatial organization

Vapor phase synthesis, characterization and gas sensing performances of Co3O4 and Au/Co3O4 nanosystems.

CVD Co3O4 Nanopyramids: a Nano‐Platform for Photo‐Assisted H2 Production