Preparation and electrochemical properties of nano-sized cryptomelane particles for the formation of potentiometric potassium ion sensors

The potentiometric response of 100-nm spherical K1.3Mn 8O16 particles versus K+ ions has been studied in aqueous media using a polymeric technology. The stoichiometry of this material evolves in potassium nitrate solution towards K1.08Mn 8O16. A stable and reversible response has been obtained with a sensitivity of 47 mV dec-1 in the range from 8 × 10 -5 to 1 mol·L-1, and a rather good selectivity towards Li+, Na+, Mg2+ and Ca2+ (logKK+/Xn+ ≈-3). We assume that this potentiometric response is the result of the ability of K1.08Mn8O16 to specifically adsorb K+ ions. © 2008 Springer-Verlag

Formation of autonomous ion sensors based on ion insertion-type materials

We describe and discuss an integrated Li-ion sensor device combining a LiFePO4 thin film prepared by pulsed laser deposition as sensing electrode and a modified ferrocene-based grafted electrode working as pseudo-reference; both were deposited onto a specific optical lithographed substrate. The simple procedure consists first of a coupling reaction at RT to form the molecule, which is grafted through a 4-h reaction with a gold substrate. Preliminary potentiometric measurements were first carried out versus a composite Bellcore electrode of Na0.33MnO2/C, and then with thin film electrodes of LiFePO4 for the detection of Na + and Li+ ions demonstrating the validity of the approach using both technologies. © 2008 Springer Science+Business Media B.V

Crystal structure and electrochemical properties vs. Na+ of the sodium fluorophosphate Na1.5VOPO4F0.5

Pure Na1.5VOPO4F0.5 was prepared by tuning the synthesis conditions previously reported by Barker et al. Using FTIR, Rietveld analysis and atomic absorption measurements, the stoichiometry and structure were unambiguously determined. The refined structure shows the same framework as the one ascribed to "NaVPO4F" but clearly underline the presence of two different sodium sites (8h and 8j), one fluorine site (2a) and one octahedral V4+ site [VO5F]. We further examined the Na+ insertion mechanism of this phase whose signature was similar to the one of "NaVPO4F" and "Na3V2(PO4)2F3". Namely two voltage plateaux are found at 3.6 and 4.0 V vs. Na+/Na and are characteristics of two bi-phasic transitions. However the overall reversible capacity does not exceed 0.56 Na ion per formula unit, and is furthermore hindered by a high voltage phenomenon, most likely linked to electrolyte degradation. Finally AC impedance measurements carried out on a dense pellet showed a RT ionic conductivity of 1.8 × 10-7   S / cm with an activation energy of 0.43 eV. © 2006 Elsevier SAS. All rights reserved

In situ measurements of Li Ion battery electrode material conductivity: Application to LixCoO2 and conversion reactions

An electrochemical cell, based on a specifically designed substrate, was used to monitor in an in situ manner the conductivity variations of various thin film electrode materials, grown by laser ablation, during their electrochemical reaction vs Li+/Li0. The validity of such a new setup was first demonstrated for the well-known LixCoO2 insertion electrode and further extended to an Fe2O3 electrode that reacts with Li through a conversion as opposed to an insertion process. For LixCoO2, a drastic increase in the conductivity near the solid solution domain was observed, confirming the insulator/metal transition previously observed near x = 0.9. For the transport properties of α-Fe2O3 thin films as a function of their Li uptake and removal, we noted the semi-metal-like behavior of the Li2O/M matrix, with room-temperature conductivity values ranging from 1 to 25 S/cm. Such results are in favor of mass transport limitations to explain high polarization observed for conversion reactions. © 2007 American Chemical Society

Study of the potentiometric response towards sodium ions of Na0.44-xMnO2 for the development of selective sodium ion sensors

Single phase Na0.44MnO2 powder was synthetized by a classical solid-state reaction. Using a plastic technology, we studied the potentiometric response versus Na+ ions in aqueous medium. A Nernstian-like response (55 mV/dec) was obtained for concentrations ranging from 1 M to 2 × 10-4 M with a quite good selectivity towards Li+, K+, Mg2+ and Ca2+. Through an ageing study of this material in aqueous solution, we clearly identified the sensing material as being the Na0.33MnO2 phase. Furthermore, we proved that the sensing activity of this compound is routed in its ability to reversibly insert/de-insert Na+ ions. © 2006 Elsevier B.V. All rights reserved

Study of the insertion/deinsertion mechanism of sodium into Na 0.44MnO2

Pure Na0.44MnO2 samples were prepared via a solid-state route by carefully tuning the synthesis conditions. Insertion/ deinsertion of sodium into the well-crystallized particles leads to capacities as high as 140 mA·h/g. A potentiostatic intermittent titration technic, together with in situ X-ray diffraction measurements, enabled us to evidence the presence of six biphasic transitions within a potential range of 2-3.8 V (vs Na+/Na). The insertion process within the Nax-MnO 2 system is fully reversible over the 0.25 < x < 0.65 composition range and presents some degree of irreversibility as values of x below 0.25 are reached. Furthermore, we similarly showed that HCl treatment has a detrimental effect on these electrochemical properties because of structural and textural evolutions. © 2007 American Chemical Society

Effect of texture on the electrochemical properties of LiFePO 4 thin films

Carbon-free in situ crystallized LiFePO 4 thin films were grown using the Pulsed Laser Deposition (PLD) technique. Adjusting the deposition time enabled the growth of films with different thicknesses. Comparing the properties of these films ((120) preferentially oriented) highlighted a relationship between microstructure and electrochemical activity. However, whatever film thickness (from 12 nm to 600 nm), the capacities recorded were far from the ones expected, since only a small percentage of the film was found to really chemically or electrochemically react. Simple experiments (creation of surface defect, metal electrodeposition, AC/DC conductivity measurements, etc.) carried out on these films gave a new insight into the origin of the limitations. The results presented herein singularly lead to the conclusion that the ionic conductivity is the main limitation for such olivine-type thin films. © 2005 Elsevier B.V. All rights reserved

Evolution of Nanostructured Manganese (Oxyhydr)oxides in Water through MnO4 - Reduction.

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Origin of electrochemical reactivity enhancement of post-annealed LiFePO4 thin films: Preparation of heterosite-type FePO4

We reported the dependence of the LiFePO4 thin films growth by Pulsed Laser Deposition (PLD) on their electrochemical properties. Whether the crystallized films are directly grown within the PLD chambers or post annealed, they present different textures and levels of surface carbon contamination, with the post-annealing films being the most contaminated. The post-annealed thermal treatment induces a drastic increase in the film electrochemical reactivity vs. Li+ (capacity 50 times higher). We show through combined cyclic voltametry and Raman spectroscopy measurements that the enhanced electrochemical activity lies in the films textural evolution. By purposely acting on the LiFePO4 film texturation we succeeded for the first time in preparing, through chemical oxidation, fully delithiated heterosite-type FePO4 thin films. Furthermore using three-electrode electrochemical impedance spectroscopy measurements on such films, we evidenced a noticeable decrease in the charge transfer resistance upon the de-insertion. Finally to account for the specific electrochemical/chemical reactivity of LiFePO4 thin films, a simple planar model is proposed. © 2006 Elsevier B.V. All rights reserved

Synthesis and electrochemical properties vs. Li of amorphous / crystallized indium vanadates

A dissolution-reprecipitation process from a mixed solution of NH4VO3 and In(NO3)3 is described for the low-temperature preparation of amorphous InVO4·2.3H2O. Crystallized phases were obtained depending on the annealing temperature of amorphous InVO4·2.3H2O. An electrochemical investigation has shown that these compounds, depending on their amorphous/crystallized nature, can react with large amounts of Li, leading to reversible capacities as large as 900 mA-h/g. Both electrochemical and in-situ X-ray diffraction studies suggest that a mechanism of Li uptake/removal, different from the usual Li insertion/deinsertion process, is occurring in these vanadates. © 1998 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint