PVDF-HFP Based, Quasi-Solid Nanocomposite Electrolytes for Lithium Metal Batteries.

Composite polymer electrolytes are systems of choice for future solid-state lithium metal batteries (LMBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is among the most interesting matrices to develop new generation quasi-solid electrolytes (QSEs). Here it is reported on nanocomposites made of PVDF-HFP and pegylated SiO2 nanoparticles. Silica-based hybrid nanofillers are obtained by grafting chains of poly(ethylene glycol) methyl ether (PEG) with different molecular weight on the surface of silica nanoparticles. The functionalized nanofiller improves the mechanical, transport and electrochemical properties of the QSEs, which show good ionic conductivity values and high resistance against dendrite penetration, ensuring boosted long and safe device operation. The most promising result is obtained by dispersing 5 wt% of SiO2 functionalized with short PEG chains (PEG750 , Mw = 750 g mol-1 ) in the PVDF-HFP matrix with an ease solvent-casting procedure. It shows ionic conductivity of 0.1 mS cm-1 at 25 °C, more than 250 h resistance to stripping/plating, and impressive results during cycling tests in LMB with LiFePO4 cathode.

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped NaxMnO2.

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.

Highly Reversible Ti/Sn Oxide Nanocomposite Electrodes for Lithium Ion Batteries Obtained by Oxidation of Ti3 Al(1-x) Snx C2 Phases.

Among the materials for the negative electrodes in Li-ion batteries, oxides capable of reacting with Li+ via intercalation/conversion/alloying are extremely interesting due to their high specific capacities but suffer from poor mechanical stability. A new way to design nanocomposites based on the (Ti/Sn)O2 system is the partial oxidation of the tin-containing MAX phase of Ti3 Al(1-x) Snx O2 composition. Exploiting this strategy, this work develops composite electrodes of (Ti/Sn)O2 and MAX phase capable of withstanding over 600 cycles in half cells with charge efficiencies higher than 99.5% and specific capacities comparable to those of graphite and higher than lithium titanate (Li4 Ti5 O12 ) or MXenes electrodes. These unprecedented electrochemical performances are also demonstrated at full cell level in the presence of a low cobalt content layered oxide and explained through an accurate chemical, morphological, and structural investigation which reveals the intimate contact between the MAX phase and the oxide particles. During the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y) Sny O2 nucleate on the surface of the unreacted MAX phase which therefore acts both as a conductive agent and as a buffer to preserve the mechanical integrity of the oxide during the lithiation and delithiation cycles.

Structure-Property Correlations in Aqueous Binary Na+/K+-CH3COO- Highly Concentrated Electrolytes.

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.

Unveiling the Role of PEO-Capped TiO2 Nanofiller in Stabilizing the Anode Interface in Lithium Metal Batteries.

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).

From Small Metal Clusters to Molecular Nanoarchitectures with a Core-Shell Structure: The Synthesis, Redox Fingerprint, Theoretical Analysis, and Solid-State Structure of [Co38As12(CO)50]4.

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.

The Missing Piece: The Structure of the Ti3C2Tx MXene and Its Behavior as Negative Electrode in Sodium Ion Batteries.

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.

Treatment with ROS detoxifying gold quantum clusters alleviates the functional decline in a mouse model of Friedreich ataxia.

Friedreich ataxia (FRDA) is caused by the reduced expression of the mitochondrial protein frataxin (FXN) due to an intronic GAA trinucleotide repeat expansion in the FXN gene. Although FRDA has no cure and few treatment options, there is research dedicated to finding an agent that can curb disease progression and address symptoms as neurobehavioral deficits, muscle endurance, and heart contractile dysfunctions. Because oxidative stress and mitochondrial dysfunctions are implicated in FRDA, we demonstrated the systemic delivery of catalysts activity of gold cluster superstructures (Au8-pXs) to improve cell response to mitochondrial reactive oxygen species and thereby alleviate FRDA-related pathology in mesenchymal stem cells from patients with FRDA. We also found that systemic injection of Au8-pXs ameliorated motor function and cardiac contractility of YG8sR mouse model that recapitulates the FRDA phenotype. These effects were associated to long-term improvement of mitochondrial functions and antioxidant cell responses. We related these events to an increased expression of frataxin, which was sustained by reduced autophagy. Overall, these results encourage further optimization of Au8-pXs in experimental clinical strategies for the treatment of FRDA.

A physico-chemical investigation of highly concentrated potassium acetate solutions towards applications in electrochemistry.

Water-in-salt solutions, i.e. solutions in which the amount of salt by volume or weight is larger than that of the solvent, are attracting increasing attention in electrochemistry due to their distinct features that often include decomposition potentials much higher than those of lower concentration solutions. Despite the high solubility of potassium acetate (KAC) in water at room temperature (up to 25 moles of salt per kg of solvent), the low cost, and the large availability, the use of highly concentrated KAC solutions is still limited to a few examples in energy storage applications and a systematic study of their physical-chemical properties is lacking. To fill this gap, we have investigated the thermal, rheological, electrical, electrochemical, and spectroscopic features of KAC/water solutions in the compositional range between 1 and 25 mol kg-1. We show the presence of a transition between the "salt-in-solvent" and "solvent-in-salt" regimes in the range of 10-15 mol kg-1. Among the explored compositions, the highest concentrations (20 and 25 mol kg-1) exhibit good room temperature conductivity values (55.6 and 31 mS cm-1, respectively) and a large electrochemical potential window (above 2.5 V).

Red phosphorus decorated electrospun carbon anodes for high efficiency lithium ion batteries.

Electrospinning is a powerful and versatile technique to produce efficient, specifically tailored and high-added value anodes for lithium ion batteries. Indeed, electrospun carbon nanofibers (CNFs) provide faster intercalation kinetics, shorter diffusion paths for ions/electrons transport and a larger number of lithium insertion sites with respect to commonly employed powder materials. With a view to further enhance battery performances, red phosphorous (RP) is considered one of the most promising materials that can be used in association with CNFs. RP/CNFs smart combinations can be exploited to overcome RP low conductivity and large volume expansion during cycling. In this context, we suggest a simple and cost effective double-step procedure to obtain high-capacity CNFs anodes and to enhance their electrochemical performances with the insertion of red phosphorous in the matrix. We propose a simple dropcasting method to confine micro- and nanosized RP particles within electrospun CNFs, thus obtaining a highly efficient, self-standing, binder-free anode. Phosphorous decorated carbon mats are characterized morphologically and tested in lithium ion batteries. Results obtained demonstrate that the reversible specific capacity and the rate capability of the obtained composite anodes is significantly improved with respect to the electrospun carbon mat alone.

Thermally Regenerable Redox Flow Battery.

The efficient production of energy from low-temperature heat sources (below 100 °C) would open the doors to the exploitation of a huge amount of heat sources such as solar, geothermal, and industrial waste heat. Thermal regenerable redox-flow batteries (TRBs) are flow batteries that store energy in concentration cells that can be recharged by distillation at temperature <100 °C, exploiting low-temperature heat sources. Using a single membrane cell setup and a suitable redox couple (LiBr/Br2 ), a TRB has been developed that is able to store a maximum volumetric energy of 25.5 Wh dm-3 , which can be delivered at a power density of 8 W m-2 . After discharging 30 % of the volumetric energy, a total heat-to-electrical energy conversion efficiency of 4 % is calculated, the highest value reported so far in harvesting of low-temperature heat.

Effect of Hematite Doping with Aliovalent Impurities on the Electrochemical Performance of α-Fe2O3@rGO-Based Anodes in Sodium-Ion Batteries.

The effect of the type of dopant (titanium and manganese) and of the reduced graphene oxide content (rGO, 30 or 50 wt %) of the α-Fe2O3@rGO nanocomposites on their microstructural properties and electrochemical performance was investigated. Nanostructured composites were synthesized by a simple one-step solvothermal method and evaluated as anode materials for sodium ion batteries. The doping does not influence the crystalline phase and morphology of the iron oxide nanoparticles, but remarkably increases stability and Coulombic efficiency with respect to the anode based on the composite α-Fe2O3@rGO. For fixed rGO content, Ti-doping improves the rate capability at lower rates, whereas Mn-doping enhances the electrode stability at higher rates, retaining a specific capacity of 56 mAhg-1 at a rate of 2C. Nanocomposites with higher rGO content exhibit better electrochemical performance.

Role of the carbon defects in the catalytic oxygen reduction by graphite nanoparticles: a spectromagnetic, electrochemical and computational integrated approach.

The chemical groups present at the surface of graphite have been thought for a long time to be mainly responsible for its catalytic activity in the oxygen reduction reaction. Recently, it was proposed that the surface defects of graphite also significantly contribute to promote this reaction. Although the behaviour of surface defects has been reported, only few comments have been dedicated to their involvement in the mechanism and the possible intermediate species in the oxygen reduction reaction. Herein, we aim to present a more detailed explanation of the catalytic activity of graphite particles based on the structure of their defects and their size. Structural, spectroscopic and magnetic investigation (X-ray diffraction, Raman and electron spin resonance) and electrochemical measurements were performed to describe the nature of the defects and their aptitude to transfer electrons. Computational description supplied precise details of the energy of the different defects and their ability to promote the reduction, also suggesting the structure of the intermediate adduct in the oxygen reduction. The results indicated that molecular oxygen preferentially interacts with graphite defects, which involve the π-electron system and accumulation of the spin density on the edges of the grains, in particular, on the zig-zag edges present on ball-milled graphite. This promotes the reactivity of this nanomaterial. Furthermore, the activation increases by decreasing the particle size.

Preparation of Naphthalene Dianhydride Bithiophene Copolymers by Direct Arylation Polycondensation and the Latent Pigment Approach.

An alternating naphthalene dianhydride bithiophene copolymer (PNDAT2) is prepared by a combined direct arylation polycondensation and the latent pigment approach. PNDAT2 is the first reported example of an alternating conjugated polymer containing naphthalene dianhydride, the oxo-analogue of naphthalene diimide often used in electron-acceptor conjugated polymers. PNDAT2 is resistant to organic solvents and can be generated directly as film by thermal treatment of the soluble tetraester precursor PNTET2. PNDAT2 is characterized by a LUMO level of -3.9 eV, similar to that of established naphthalene diimide containing soluble copolymers. This route to insoluble electron acceptor copolymers by thermal cleavage of soluble precursors is an alternative to classical cross-linking or orthogonal processing strategies.

Preparation of Naphthalene Dianhydride Bithiophene Copolymers by Direct Arylation Polycondensation and the Latent Pigment Approach.

Invited for this month's cover are the collaborating groups of Prof. Luca Beverina from the University of Molani-Bicocca, Italy and Prof. Michael Sommer from Chemnitz University of Technology, Germany. The front cover shows the thermally induced transformation of a soluble and electron-rich naphthalene tetraester-bithiophene copolymer into the corresponding insoluble and electron-poor naphthalenetetraanhydride derivative. The combination of monochromatic squares, inspired by the work of Josef Albers, shows the color change involved in the transformation. Read the full text of the article at 10.1002/cplu.201900210.

An Integrated Theoretical/Experimental Study of Quinolinic-Isoquinolinic Derivatives Acting as Reversible Electrochromes.

A series of compounds, featuring an ethenylic bridge and quinoline and isoquinoline end capping units possessing systematically varied substitution patterns, were prepared as molecular materials for electrochromic applications. The different structures were optimized in order to maximize the electrochromic contrast in the visible region, mostly by achieving a completely UV-absorbing oxidized state. Density functional theory (DFT) calculations are exploited in order to rationalize the correlation between the molecular structure, the functional groups' electronic properties, and the electrochemical behavior. It is shown that the molecular planarity (i.e. ring/ring π conjugation) plays a major role in defining the mechanism of the electrochemical charge transfer reaction, while the substituent's nature has an influence on the LUMO energy. Among the compounds here studied, the (E)-10-methyl-9-(2-(2-methylisoquinolinium-1-yl)-vinyl)-1,2,3,4-tetrahydroacri-dinium trifluoromethanesulfonate derivative shows the most interesting properties as an electrochromophore.

Anharmonic motions versus dynamic disorder at the Mg ion from the charge densities in pyrope (Mg3Al2Si3O12) crystals at 30†K: six of one, half a dozen of the other.

The possible occurrence of static/dynamic disorder at the Mg site in pyrope (Mg3Al2Si3O12), with or without anharmonic contribution to the thermal vibrations even at low temperatures, has been largely debated but conclusions were contrasting. Here a report is given on the experimental charge density distribution, ρEXP, of synthetic pyrope at T = 30 K, built through a Stewart multipolar expansion up to l = 5 and based on a very precise and accurate set of in-home measured single-crystal X-ray diffraction amplitudes with a maximum resolution of 0.44 Å. Local and integral topological properties of ρEXP are in substantial agreement with those of ρTHEO, the corresponding DFT-grade quantum charge density of an ideal pyrope crystal, and those derived from synchrotron investigations of chemical bonding in olivines. Relevant thermal atomic displacements, probably anharmonic in nature, clearly affect the whole structure down to 30 K. No significant (> 2.5σ) residual Fourier peaks are detectable from the ρEXP distribution around Mg, after least-squares refinement of a multipole model with anharmonic thermal motion at the Mg site. Experimental findings were confirmed by a full analysis of normal vibration modes of the DFT-optimized structure of the perfect pyrope crystal. Mg undergoes wide displacements from its equilibrium position even at very low temperatures, as it is allocated in a ∼ 4.5 Šlarge dodecahedral cavity and involved in several soft phonon modes. Implications on the interplay among static/dynamic disorder of Mg and lattice vibrational degrees of freedom are discussed.

Shape-Controlled TiO2 Nanocrystals for Na-Ion Battery Electrodes: The Role of Different Exposed Crystal Facets on the Electrochemical Properties.

Rechargeable sodium-ion batteries are becoming a viable alternative to lithium-based technology in energy storage strategies, due to the wide abundance of sodium raw material. In the past decade, this has generated a boom of research interest in such systems. Notwithstanding the large number of research papers concerning sodium-ion battery electrodes, the development of a low-cost, well-performing anode material remains the largest obstacle to overcome. Although the well-known anatase, one of the allotropic forms of natural TiO2, was recently proposed for such applications, the material generally suffers from reduced cyclability and limited power, due to kinetic drawbacks and to its poor charge transport properties. A systematic approach in the morphological tuning of the anatase nanocrystals is needed, to optimize its structural features toward the electrochemical properties and to promote the material interaction with the conductive network and the electrolyte. Aiming to face with these issues, we were able to obtain a fine tuning of the nanoparticle morphology and to expose the most favorable nanocrystal facets to the electrolyte and to the conductive wrapping agent (graphene), thus overcoming the intrinsic limits of anatase transport properties. The result is a TiO2-based composite electrode able to deliver an outstandingly stability over cycles (150 mA h g-1 for more than 600 cycles in the 1.5-0.1 V potential range) never achieved with such a low content of carbonaceous substrate (5%). Moreover, it has been demonstrated for the first time than these outstanding performances are not simply related to the overall surface area of the different morphologies but have to be directly related to the peculiar surface characteristics of the crystals.

Tuning Thiophene-Based Phenothiazines for Stable Photocatalytic Hydrogen Production.

Dibranched donor-(π-acceptor)2 dyes, where phenothiazine is the donor core, cyanoacrylic acid is the acceptor/anchoring group, and π is represented by mono- and poly-cyclic simple and fused thiophene derivatives, were tested as photosensitizers in the photocatalytic production of H2 , in combination with a Pt/TiO2 catalyst. The optical and electrochemical properties of the dyes were investigated, showing that careful design of the thiophene-based π spacer afforded enhanced optical properties. In the H2 production over 20 h, the new thiophene-based sensitizers revealed improved stability after longer irradiation times and enhanced performances, in terms of H2 production rates and light-to-fuel efficiencies, after an initial activation period, which were for the first time associated with enhanced stability under photocatalytic production of H2 and the absence of critical dye degradation.

A new method and tool for detection and quantification of PM oxidative potential.

Airborne particulate matter (PM) contains several quinones, which are able to generate reactive oxygen species impacting on cell viability. A method able to detect and quantify PM oxidative potential, based on the cytochrome c (cyt-c) reduction by means of superoxide anion produced through quinones redox cycling in the presence of reducing agents, is here described. Tris(2-carboxyethyl)phosphine resulted to be the most efficient reducing agent among the ones tested. The procedure included rapid particles extraction, followed by two alternative analytical methods, a spectrophotometric assay based on the initial rate of cyt-c reduction at 550 nm, and an amperometric assay, based on self-assembled monolayers modified gold electrodes. The smallest amount of PM needed to obtain an evaluable signal is 2 µg. The described procedure may represent a starting point to develop devices for PM measurements in polluted atmospheric environments.