Marco Giorgetti

In Situ X‐Ray Absorption Spectroscopy Characterization of V 2 O 5 Xerogel Cathodes upon Lithium Intercalation

Vanadium pentoxide materials prepared through sol-gel processes act as excellent intercalation hosts for lithium as well as for polyvalent cations. Previous ex situ X-ray absorption spectroscopy and X-ray diffraction characterizations have shown that the electrochemical performance of vanadium pentoxide xerogels depends inversely on the long-range order of the V{sub 2}O{sub 5}-layered structure. Recently, new ways to prevent the self-organization of the dry materials, which takes place upon water removal from the starting hydrogel, have been introduced. In the present paper the authors report on the in situ X-ray absorption spectroscopy characterization of a spray-coated V{sub 2}O{sub 5} (freeze-dried) xerogel cathode upon lithium intercalation.

Layered-double-hydroxide-modified electrodes: electroanalytical applications

AbstractTwo-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example. Figure 

Electrochemical characterisation of Ni/AlX hydrotalcites and their electrocatalytic behaviour

Abstract Some ‘conductive’ hydrotalcites containing nickel as divalent cation and Cl − , SO 4 2− or CO 3 2− as interlayer anion, have been synthesised and membranised with different types of polymeric matrices to modify glassy carbon electrodes. The mechanism responsible of the conductive properties has been deeply investigated by voltammetric techniques using both a stationary and a rotating disk electrode, demonstrating that the interlayer anion does not affect significantly the electrochemical behaviour of the material. The electrocatalytic properties have been also studied pointing out the key role of the steric hindrance of the oxidisable substrate. In particular, mono- and polyhydric compounds have been taken into account. As to the electrocatalytic efficiency, the nature of the interlayer anion and, hence, the dimension of the interlayer spacing, is important in determining the sensitivity of the measurement since it can affect the analyte diffusion inside the hydrotalcite structure.

Hybrid Metal Cyanometallates Electrochemical Charging and Spectrochemical Identity of Heteronuclear Nickel/Cobalt Hexacyanoferrate

Hybrid metal nickel/cobalt hexacyanoferrate (Ni/CoHCNFe) has been prepared in the form of thin films on electrode surfaces and as bulk precipitates (powders). This heteronuclear metal hexacyanoferrate cannot be considered a simple mixture of hexacyanoferrates of nickel and cobalt, and it shows different voltammetric and electrochromic characteristics in comparison to the respective single-metal hexacyanoferrates. On the basis of X-ray absorption, elemental analysis, and comparative voltammetric measurements, the following approximate formulas, K 2 Ni 0.5 II Co 0.5 II [Fe II (CN)] 6 and KNi 0.5 II Co 0.5 II [Fe III (CN) 6 ], have been proposed for the predominant reduced and oxidized forms of hybrid Ni/CoHCNFe. The results are consistent with the existence of linear units -Fe-CN-Co-NC-Fe-CN-Ni- in the structure. Hybrid nickel/cobalt hexacyanoferrate film has unique electrochromic properties, and it shows long-term stability and promising charge storage/transport capabilities during voltammetric potential cycling.

Evidence of four-body contributions in the EXAFS spectrum of Na2Co[Fe(CN)6]

Abstract This contribution deals with an EXAFS investigation of Na 2 Co[Fe(CN) 6 ] at the K-edges of both Fe and Co. Na 2 Co[Fe(CN) 6 ], a well known and easily prepared mixed hexacyanoferrate, is characterised by a unit cell containing linear “FeCNCo” chains where a super-focusing effect may be observed at the K-edge of both transition metals. The multiple scattering (MS) signal intensity associated with the linear chain (four body contribution) is comparable with the first shell contributions. The combined fit over two edges, the intensity of the MS signal and the large number of experimental points included in the fit, permit an accurate extraction of the structural parameters at the limit of the EXAFS sensitivity.

In Vitro and in Vivo Anticancer Activity of Copper(I) Complexes with Homoscorpionate Tridentate Tris(pyrazolyl)borate and Auxiliary Monodentate Phosphine Ligands

Tetrahedral copper(I) TpCuP complexes 1-15, where Tp is a N,N,N-tris(azolyl)borate and P is a tertiary phosphine, have been synthesized and characterized by means of NMR, ESI-MS, and XAS-EXAFS, and X-ray diffraction analyses on the representative complexes 1 and 10, respectively. All copper(I) complexes were evaluated for their antiproliferative activity against a panel of human cancer cell lines (including cisplatin and multidrug-resistant sublines). The two most effective complexes [HB(pz)3]Cu(PCN), 1, and [HB(pz)3]Cu(PTA), 2, showed selectivity toward tumor vs normal cells, inhibition of 26S proteasome activity associated with endoplasmic reticulum (ER) stress, and unfolded protein response (UPR) activation. No biochemical hallmarks of apoptosis were detected, and morphology studies revealed an extensive cytoplasmic vacuolization coherently with a paraptosis-like cell death mechanism. Finally, the antitumor efficacy of complex 1 was validated in the murine Lewis Lung Carcinoma (LLC) model.

Evidence for Reversible Formation of Metallic Cu in Cu0.1 V 2 O 5 Xerogel Cathodes during Intercalation Cycling of Li + Ions as Detected by X-Ray Absorption Spectroscopy

Vanadium pentoxide materials prepared through sol-gel processes (xerogel, aerogel, and aerogel-like) act as excellent intercalation hosts for lithium as well as polyvalent cations. The large lithium insertion capacity of these materials makes them attractive for use as cathodes in high-capacity lithium batteries. Copper-doped V 2 O 5 -based cathodes have excellent properties in terms of high intercalation rate and very good reversibility upon cycling with no capacity fading after more than 450 cycles. This paper reports in situ X-ray absorption spectroscopy (XAS) investigations of copper-doped V 2 O 5 xerogel. The K-edge X-ray absorption thresholds of V and Cu were studied. The local structure around copper is found to change dramatically during individual insertion/ release cycles for Li + ions, The XAS analysis indicates that the lithiation of the Cu 0.1 V 2 O 5 xerogel cathode proceeds with concurrent formation of copper metal. However, the starting compound is regenerated upon releasing the inserted lithium (charging the cathode). thus revealing the foundation for excellent structural and electronic reversibility of the material.

Multivariate Curve Resolution Analysis for Interpretation of Dynamic Cu K-Edge X-ray Absorption Spectroscopy Spectra for a Cu Doped V2O5 Lithium Battery

Vanadium pentoxide materials prepared through sol-gel processes act as excellent intercalation hosts for lithium as well as polyvalent cations. A chemometric approach has been applied to study the X-ray absorption near-edge structure (XANES) evolution during in situ scanning of the Cu(0.1)V(2)O(5) xerogel/Li ions battery. Among the more common techniques, the fixed size windows evolving factor analysis (FSWEFA) permits the number of species involved in the experiment to be determined and the range of existence of each of them. This result, combined with the constraints of the invariance of the total concentration and non-negativity of both concentrations and spectra, enabled us to obtain the spectra of the pure components using a multivariate curve resolution refined by an alternate least squares fitting procedure. This allowed the normalized concentration profile to be understood. This data treatment evidenced the occurrence, for the first time, of three species during the battery charging. This fact finds confirmation by comparison of the pure spectra with the experimental ones. Extended X-ray absorption fine structure (EXAFS) analysis confirms the occurrence of three different chemical environments of Cu during battery charging.

Synthesis Route to Supported Gold Nanoparticle Layered Double Hydroxides as Efficient Catalysts in the Electrooxidation of Methanol

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells.

AC impedance study of a synthetic hydrotalcite-like compound modified electrode in aqueous solution

This paper deals with the electrochemical characterisation of Ni/Al/Cl hydrotalcite modified electrodes. The electrochemical impedance spectroscopy technique has been used in order to study the electronic and ionic conduction, both inside and on the surface of the material. The electronic and ionic contributions have been separated and the behaviour of the respective parameters has been studied as a function of the potential. In order to determine the kinetic limiting step of the overall electrochemical process we performed experiments at different temperatures, and calculated the activation energies of the electron hopping process and ion transport process. In addition we studied the behaviour of the system at different OH concentrations (pH 9.7/12.8) with the aim of clarifying the role of OH ions in the electrochemical process. # 2003 Elsevier Science Ltd. All rights reserved.