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Highly concentrated aqueous binary solutions of acetate salts are promising systems for different electrochemical applications, for example, energy storage devices. The very high solubility of CH3COOK allows us to obtain water-in-salt electrolyte concentrations, thus reducing ion activity and extending the cathodic stability of an aqueous electrolyte. At the same time, the presence of Li+ or Na+ makes these solutions compatible with intercalation materials for the development of rechargeable alkaline-ion batteries. Although there is a growing interest in these systems, a fundamental understanding of their physicochemical properties is still lacking. Here, we report and discuss the physicochemical and electrochemical properties of a series of solutions based on 20 mol kg-1 CH3COOK with different concentrations of CH3COONa. The most concentrated solution, 20 mol kg-1 CH3COOK + 7 mol kg-1 CH3COONa, gives the best compromise between transport properties and electrochemical stability, displaying a conductivity of 21.2 mS cm-1 at 25 °C and a stability window of up to 3 V in “ideal” conditions, i.e., using a small surface area and highly electrocatalytic electrode in a flooded cell. Careful Raman spectroscopy analyses help to address the interaction network, the phase evolution with temperature, and the crystallization kinetics.

Sodium-ion batteries have recently aroused the interest of industries as possible replacements for lithium-ion batteries in some areas. With their high theoretical capacities and competitive prices, P2-type layered oxides (NaxTMO2) are among the obvious choices in terms of cathode materials. On the other hand, many of these materials are unstable in air due to their reactivity toward water and carbon dioxide. Here, Na0.67Mn0.9Ni0.1O2 (NMNO), one of such materials, has been synthesized by a classic sol-gel method and then exposed to air for several weeks as a way to allow a simple and reproducible transition toward a Na-rich birnessite phase. The transition between the anhydrous P2 to the hydrated birnessite structure has been followed via periodic XRD analyses, as well as neutron diffraction ones. Extensive electrochemical characterizations of both pristine NMNO and the air-exposed one vs sodium in organic medium showed comparable performances, with capacities fading from 140 to 60 mAh g-1 in around 100 cycles. Structural evolution of the air-exposed NMNO has been investigated both with ex situ synchrotron XRD and Raman. Finally, DFT analyses showed similar charge compensation mechanisms between P2 and birnessite phases, providing a reason for the similarities between the electrochemical properties of both materials.

The cluster [Co38As12(CO)50]4- was obtained by pyrolysis of [Co6As(CO)16]-. The metal cage features a closed-packed core inside a Co/As shell that progressively deforms from a cubic face-centered symmetry. The redox and acid-base reactivities were determined by cyclic voltammetry and spectrophotometric titrations. The calculated electron density revealed the shell-constrained distribution of the atomic charges, induced by the presence of arsenic.

Lithium metal batteries (LMBs) will be a breakthrough in automotive applications, but they require the development of next-generation solid-state electrolytes (SSEs) to stabilize the anode interface. Polymer-in-ceramic PEO/TiO2 nanocomposite SSEs show outstanding properties, allowing unprecedented LMBs durability and self-healing capabilities. However, the mechanism underlying the inhibition/delay of dendrite growth is not well understood. In fact, the inorganic phase could act as both a chemical and a mechanical barrier to dendrite propagation. Combining advanced in situ and ex situ experimental techniques, we demonstrate that oligo(ethylene oxide)-capped TiO2, although chemically inert toward lithium metal, imparts SSE with mechanical and dynamical properties particularly favorable for application. The self-healing characteristics are due to the interplay between mechanical robustness and high local polymer mobility which promotes the disruption of the electric continuity of the lithium dendrites (razor effect).

The most common MXene composition Ti3C2Tx (T = F, O) shows outstanding stability as anode for sodium ion batteries (100% of capacity retention after 530 cycles with charge efficiency >99.7%). However, the reversibility of the intercalation/deintercalation process is strongly affected by the synthesis parameters determining, in turn, significant differences in the material structure. This study proposes a new approach to identify the crystal features influencing the performances, using a structural model built with a multitechnique approach that allows exploring the short-range order of the lamella. The model is then used to determine the long-range order by inserting defective elements into the structure. With this strategy it is possible to fit the MXene diffraction patterns, obtain the structural parameters including the stoichiometric composition of the terminations (neutron data), and quantify the structural disorder which can be used to discriminate the phases with the best electrochemical properties.

Lithium was found to be inserted into FeNb11O29 by reaction with n-butyllithium, producing Li11FeNb11O 29 samples with good crystallinity, and the Amma crystallographic- shear structures of both compounds (a = 28.7093(6)/28.4036(4), b = 3.8256(1)/4.08447(9), c = 20.6241(4)/20.7067(2) Å, respectively) were Rietveld-refined by high-resolution neutron powder diffraction. Lithium atoms of Li11FeNb11O29 were located both in 4-fold- and in 5-fold-coordinated positions, lying respectively inside and between the 4 × 3 perovskite blocks of Nb(Fe)O6 octahedra. Electrochemical measurements on a FeNb11O29/ LixFeNb 11O29 electrode vs metallic Li showed that lithium can be intercalated/deintercalated reversibly in the 1.1-2.5 V range with a stable capacity of 185 mAh/g, which roughly corresponds to 11 Li atoms per f.u. as obtained by chemical lithiation. The rather uniform structural distribution found for Li atoms is consistent with the good electrode reversibility, which makes this material promising as anode in rechargeable lithium batteries. © 2014 American Chemical Society.

A new versatile thiophene derivative exomethylene-3,4- ethylenedioxythiophene (emEDOT) is introduced. The molecule can be straightforwardly prepared in two steps from commercially available derivatives and enables facile further derivatization through both acid catalyzed additions of alcohols and standard thiol-ene click chemistry. The preparation of electrochromic materials and of an electrochemical avidine sensor is shown by the oxidative polymerizations of several functionalized EDOT monomers straightforwardly prepared from emEDOT

Macroporous WO3 films with inverted opal structure were synthesized by one-step procedure, which involves the self-assembly of the spherical templating agents and the simultaneous sol-gel condensation of the semiconductor alkoxide precursor. Transition metal doping, aimed to enhance the WO3 electrical response, was carried out by including Cr(III) and Pt(IV) centers in the oxide matrix. It turned out that Cr remains as homogeneously dispersed Cr(III) centers inside the WO3 host, while Pt undergoes reduction and aggregation to form nanoclusters located at the oxide surface. Upon interaction with NH3, the electrical conductivity of transition metal doped-WO3 increases, especially in the presence of Pt dopant, resulting in outstanding sensing properties (S = 110 ± 15 at T = 225 °C and [NH3] = 74 ppm). A mechanism was suggested to explain the excellent electrical response of Pt-doped films with respect to the Cr-doped ones. This associates the easy chemisorption of ammonia on the WO 3 nanocrystals, promoted by the inverted opal structure, with the catalytic action exerted by the surface Pt nanoclusters on the N-H bond dissociation. The overall results indicate that in Pt-doped WO3 films the effects of the macroporosity positively combine with the electrical sensitization promoted by the metal nanoclusters, thus providing very lightweight materials which display high functionality even at relatively low temperatures. We expect that this synergistic effect can be exploited to realize other functional hierarchical metal oxide structures to be used as gas sensors or catalysts.(Figure Presented) © 2011 American Chemical Society.

Squaraines have been known for many decades as very stable and versatile vis-NIR absorbing dyes. They have found applications for example as sensitizers in organic photovoltaics and photodetectors. The most common squaraine structure is the 1,3-regioisomer. Their 1,2-regioisomers are seldom mentioned and unanimously regarded as side products. A facile direct synthesis of 1,2-squaraines, highlighting the role played by reaction conditions and electronic factors, is described. The first electrochemical characterization of these dyes is also shown. © 2011 American Chemical Society.

Two heteroarylene-vinylene donor-acceptor polymers, P(2, 6-Py-V-EDOT) and P(2, 5-Py- V-EDOT), containing vinylene-spaced simple donor (EDOT) and acceptor (pyridine) moieties, are presented. The central pyridine ring of the repeating unit is either 2, 6- or 2, 5-substituted, leading to different structural and electronic properties of the monomers. Polymers were obtained by either oxidative electro- polymerization or Yamamoto coupling and fully characterized by NMR, UV-vis absorption, GPC, TGA, DSC, electrochemistry, and spectroelectrochemistry. Detailed ab initio computations have been performed for the monomers and model oligomers for analyzing their optical and electronic properties. GPC showed that isolated polymers obtained via Yamamoto poly coupling have low molecular weights, likely due to solubility issues. The electrochemical polymerizations led to p- and n-dopable polymers, with 2, 5-Py-V- EDOT yielding more reversible n-doped process. The energetic positions revealed HOMO (-5.1 and -5.0 eV), LUMO (-3.4 eV), and narrow bandgap (1.6 and 1.7 eV) energies closely matching materials-design rules for optimized organic photovoltaic devices. Preliminary investigation in photovoltaic devices in combination with C71-PCBM afforded relatively modest power conversion efficiencies of ∼0.5% (AM 1.5G, 100 mW/cm2), which were attributed to the low molecular-weight of the polymers accessible via the chemical route. © 2010 American Chemical Society.

A new, fast, one-pot synthesis of SnO2 and Pt-doped SnO2 inverted opal thin films, to be used as materials for gas sensing, was carried out. Films were built from crystalline cassiterite nanoparticles, uniform in size (∼5 nm), resulting in a well-organized hierarchical structure of macro- and mesopores. The noble metal was homogeneously dispersed into the sensing layer of the oxide and the doping centers were present as Pt(IV) and Pt(II) species, partially reduced to Pt(0) after the interaction with the reducing gas (CO). The values of the electrical sensitivity under CO/Air atmosphere demonstrated that the response of Pt-doped films is higher than that of bare SnO2 films, and that the response of inverted opal films is higher compared to that of the sol-gel films. The regular array of cassiterite nanoparticles, strongly interconnected and ordered as close-packed hollow spheres, promotes the effective gas diffusion through the oxide layer and, along with the electron acceptor ability of Pt(IV) doping centers, significantly contributes to enhancing the electrical sensitivity. The conductance regime of the Pt-doped SnO2 inverted opal film is indicative of a regular microstructure of SnO2 nanoparticles

Silicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4200 mAh/g). However silicon’s large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. Designing nanoscale hierarchical structures is a novel approach to address the issues associated with the large volume changes. In this letter, we introduce a core−shell design of silicon nanowires for highpower and long-life lithium battery electrodes. Silicon crystalline-amorphous core−shell nanowires were grown directly on stainless steel current collectors by a simple one-step synthesis. Amorphous Si shells instead of crystalline Si cores can be selected to be electrochemically active due to the difference of their lithiation potentials. Therefore, crystalline Si cores function as a stable mechanical support and an efficient electrical conducting pathway while amorphous shells store Li+ ions. We demonstrate here that these core−shell nanowires have high charge storage capacity (1000 mAh/g, 3 times of carbon) with 90% capacity retention over 100 cycles. They also show excellent electrochemical performance at high rate charging and discharging (6.8 A/g, 20 times of carbon at 1 h rate).

The impedance behavior of silicon nanowire electrodes has been investigated to understand the electrochemical process kinetics that influences the performance when used as a high-capacity anode in a lithium ion battery. The ac response was measured by using impedance spectroscopy in equilibrium conditions at different lithium compositions and during several cycles of charge and discharge in a half cell vs. metallic lithium. The impedance analysis shows the contribution of both surface resistance and solid state diffusion through the bulk of the nanowires. The surface process is dominated by a solid electrolyte layer (SEI) consisting of an inner, inorganic insoluble part and several organic compounds at the outer interface, as seen by XPS analysis. The surface resistivity, which seems to be correlated with the Coulombic efficiency of the electrode, grows at very high lithium contents due to an increase in the inorganic SEI thickness. We estimate the diffusion coefficient of about 2 × 10−10 cm2/s for lithium diffusion in silicon. A large increase in the electrode impedance was observed at very low lithium compositions, probably due to a different mechanism for lithium diffusion inside the wires. Restricting the discharge voltage to 0.7 V prevents this large impedance and improves the electrode lifetime. Cells cycled between 0.07 and 0.70 V vs. metallic lithium at a current density of 0.84 A/g (C/5) showed good Coulombic efficiency (about 99%) and maintained a capacity of about 2000 mAh/g after 80 cycles.

The mechanism of NO interaction with nanosized Ru(Pd,Pt)-doped SnO2 was studied by electron paramagnetic resonance, Mo ̈ssbauer, and electric resistance measurements. Three steps were proposed for the reaction between the semiconductor oxide and the gaseous component: (i) the formation of bielectronic oxygen vacancies (Vo) in SnO2; (ii) their single-ionization (Vo ¥) with injection of electrons into the SnO2 conduction band; (iii) the subsequent transfer of electrons from Vo ¥ to [Ru(Pd,Pt)]4+. The last process induces the formation of further oxygen vacancies which reduce the transition metal centers to lower oxidation states; the redox processes is enhanced and the electrical resistance in transition metal-doped SnO2 is stronger modified with respect to the undoped material.

Tin dioxide and ruthenium(platinum)-doped tin dioxide were synthesized in the form of inverted opals, aiming to investigate the interaction of these materials with CO reducing gas. The results of electron paramagnetic resonance (EPR) investigation allowed us to conclude that CO interaction causes the formation of singly ionized oxygen vacancies located in the subsurface region. These ones transfer their electrons to transition metal centers, Ru or Pt, enhancing the SnO2 surface reactivity toward CO. The reduction of Ru4+ and Pt4+ was assessed both by EPR and Mössbauer spectroscopy. Resistance measurements showed that the materials are well-suitable for use in CO sensor devices because of their reproducible and fast electrical response; this was related to the homogeneous and high dispersion of Ru and Pt centers in the oxide matrix and to the subsurface location of the species active in the electron-transfer processes. © 2005 American Chemical Society.

The thermal evolution of sol-gel SnO2-based thin films was explored by investigating their structural and morphological features. Nanostructured SnO2 and Pt-doped SnO2 layers were obtained using tetra(tert-butoxy)tin(IV) and Pt(II) acetlylacetonate as precursors. Films were prepared by spin coating from ethanol solutions with different viscosity. After drying at room temperature, they were annealed in air at 673 and 973 K. The surface morphology was analyzed by scanning electron microscopy, atomic force microscopy, and scanning near-field optical microscopy. The structural characterization was performed by means of glancing incidence X-ray diffraction and microdiffraction. Both drying at room temperature and thermal treatment at 673 K resulted in the formation of holes on the surface and inside the films. Their distribution and average dimension were found to depend mainly on the viscosity of the sol precursor, and on the presence of Pt in the films. After annealing at 973 K, surface segregation of PtOx phases and partial filling of the surface holes occurred. The effects of morphology on the electrical transport properties are discussed on the basis of sensitivity, S, measurements (S = Rair/RCO where Rair and RCO stand for the resistance in air and CO/air, respectively).