Characterization of Mn species in mesoporous systems: An electrochemical study

Siliceous (MCM-41 type) and aluminophosphate (AlPO type) mesoporous materials have been synthesized trying to substitute the largest amount of Si and Al with Mn.

The MnMCM-41 and MnAlPO obtained samples were characterized from the structural viewpoint and successively they underwent electrochemical testing by means of cyclic voltammetries in aqueous electrolytes in order to evaluate the electrochemical activity of the transition metal. In this communication, we report the results obtained from the structural and electrochemical characterization of these samples. The samples show the expected mesoporous structure with hexagonal array. In both systems, Mn is electrochemically active. In MnMCM-41 the two Mn(IV)/Mn(III) and Mn(III)/Mn(II) processes can be detected, while in MnAlPO Mn(III), originally present, shows only the Mn(IV)/Mn(III) reaction.     

A New Design Paradigm for Smart Windows: Photocurable Polymers for Quasi‐Solid Photoelectrochromic Devices with Excellent Long‐Term Stability under Real Outdoor Operating Conditions

A new photoelectrochromic device (PECD) is presented in this work proposing the combination of a WO₃‐based electrochromic device (ECD) and a polymer‐based dye‐sensitized solar cell (DSSC). In the newly designed architecture, a photocurable polymeric membrane is employed as quasi‐solid electrolyte for both the ECD and the DSSC. In addition, a photocurable fluoropolymeric system is incorporated as solution‐processable external protective thin coating film with easy‐cleaning and UV‐shielding functionalities. Such new polymer‐based device assembly is characterized by excellent device operation with improved photocoloration efficiency and switching ability compared with analogous PECDs based on standard liquid electrolyte systems. In addition, long‐term (>2100 h) stability tests under continuous exposure to real outdoor conditions reveal the remarkable performance stability of this new quasi‐solid PECD system, attributed to the protective action of the photocurable fluorinated coating that effectively prevents photochemical and physical degradation of the PECD components during operation. This first example of quasi‐solid PECD systems paves the way for a new generation of thermally, electrochemically, and photochemically stable polymer‐based PECDs, and provides for the first time a clear demonstration of their true potential as readily upscalable smart window components for energy‐saving buildings.     

Microfibrillated cellulose as reinforcement for Li-ion battery polymer electrolytes with excellent mechanical stability

Methacrylic-based thermo-set gel-polymer electrolyte membranes obtained by a very easy, fast and reliable free radical photo-polymerisation process and reinforced with microfibrillated cellulose particles are here presented. The morphology of the composite electrolytes is investigated by scanning electron microscopy and their thermal behaviour (characteristic temperatures, degradation temperature) are investigated by thermo-gravimetric analysis and differential scanning calorimetry. The composite membranes prepared exhibit excellent mechanical properties, with a Young's modulus as high as about 80 MPa at ambient temperature. High ionic conductivity (approaching 10⁻³ S cm⁻¹ at 25 °C) and good overall electrochemical performances are maintained, enlightening that such specific approach would make these hybrid organic, cellulose-based composite polymer electrolyte systems a strong contender in the field of thin and flexible lithium based power sources.     

Unveiling the controversial mechanism of reversible Na storage in TiO2 nanotube arrays: Amorphous versus anatase TiO2

Due to their inherent safety,low cost,and structural stability,TiO2 nanostructures represent a suitable choice as anode materials in sodium-ion batteries.In the recent years,various hypotheses have been proposed regarding the actual mechanism of the reversible insertion of sodium ions in the TiO2 structure,and previous reports are often controversial in this respect.Interestingly,when tested as binder-and conducting additive-free electrodes in laboratory-scale sodium cells,amorphous and crystalline (anatase) TiO2 nanotubular arrays obtained by simple anodic oxidation exhibit peculiar and intrinsically different electrochemical responses.In particular,after the initial electrochemical activation,anatase TiO2 shows excellent rate capability and very stable long-term cycling performance with larger specific capacities,and thus a clearly superior response compared with the amorphous counterpart.To obtain deeper insight,the present materials are thoroughly characterized by scanning electron microscopy and ex situ X-ray diffraction,and the insertion of sodium ions in the TiO2 bulk phases is systematically modeled by density functional theory calculations.The present results may contribute to the development of more systematic screening approaches to identify suitable active materials for highly efficient sodium-based energy storage systems.     

Highly ionic conducting methacrylic-based gel-polymer electrolytes by UV-curing technique

Today, special interest is focused on polymer systems showing high ionic conductivity at ambient and/or sub ambient temperatures, since they find unique practical applications, such as separators in high power, versatile, rechargeable Li-based batteries. Thermo-set membranes prepared by free radical photo polymerisation (UV-curing) could be an interesting alternative to existing polymer electrolytes. In the present paper, we report the application of this technique to the synthesis of gel-polymer membranes which can be used as electrolytes for lithium battery application. These membranes are prepared by mixing a dimethacrylic (BEMA) and/or a diacrylic monomer (PEGDA), a methacrylic reactive diluent (PEGMA) and a radical photo-initiator with the in situ addition of a EC/DEC solution. The above mixtures are UV irradiated to obtain transparent, flexible, easy to handle gel-polymer films. The gel-polymer electrolytes (GPEs) are then prepared by swelling these membranes in different liquid electrolytes. The results obtained indicate some superior and satisfactory performances in terms of ionic conductivity at ambient temperature for various GPEs prepared with different lithium salt solutions. The relevance of these features in view of practical application is here demonstrated by the response of lithium cells based on prepared GPEs.     

Novel multiphase electrode/electrolyte composites for next generation of flexible polymeric Li-ion cells

An innovative multiphase electrode/electrolyte composite is proposed here, which is obtained by a fast, versatile and easily scalable UV-induced free-radical photo-polymerisation technique. This novel configuration consists of a methacrylic-based polymer electrolyte directly formed in situ at the interface of different electrode films (i.e. commercial graphite and hydrothermally synthesized LiFePO₄). Conformal coatings are confirmed by SEM analysis which indicates an intimate interfacial adhesion between the electrode material particles and the polymer electrolyte. Laboratory-scale lithium pouch cells assembled by contacting a lithium metal counter electrode over the as-prepared electrode/electrolyte composites display good ambient temperature charge/discharge characteristics, at the level of the corresponding lithium cells in liquid electrolyte, along with very stable cyclability even at high current rates. In addition, preliminary results of a laboratory-scale Li-ion polymer cell, assembled by contacting the LiFePO₄ cathode with the graphite anode, both in situ coated with the polymer electrolyte, are presented. The obtained findings outline the practical relevance of the novel procedure adopted which leads to the preparation of composite films with interesting performance, particularly for the next generation of flexible all-solid-state Li-ion microbatteries.     

Pd/SiO2 as Heterogeneous Catalyst for the Heck Reaction: Evidence for a Sensitivity to the Surface Structure of Supported Particles

The contact of Pd(AcO)₂ in solution with thiouric tethered to a silica led to the formation of supported nanoparticles (ca. 2 nm in size) active in the Heck reaction, quite sensitive to the palladium leaching. A stable supported phase was obtained by subsequent calcination, but the catalytic activity resulted strongly dependent on the calcination temperature. Such a behaviour was related to differences in the surface structure of the supported particles, as those monitored by IR spectroscopy of CO adsorbed on catalysts reduced at various temperatures.     

UV-cured polymer electrolytes encompassing hydrophobic room temperature ionic liquid for lithium batteries

We demonstrate herewith the application of in situ one-shot free radical photo-polymerisation (UV-curing) process to incorporate room temperature ionic liquids (RTILs) into polymer membranes which can be used as electrolytes for lithium-based batteries. The reactive formulation for the preparation of the polymer membranes was based on a dimethacrylic oligomer (BEMA). The polymer electrolyte membranes were synthesized by UV radiating a mixture of BEMA and a proper radical photo-initiator with different compositions of 1-ethyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide [EMIPFSI] and, additionally, LiTFSI as lithium source.Stable and flexible polymer films with good mechanical integrity can easily be produced with varying the EMIPFSI content by using this method. Remarkable values of ionic conductivity were obtained even at ambient temperature. Galvanostatic charge/discharge cyclability tests were performed on the polymer electrolyte membranes by constructing a cell using LiFePO₄ as cathode and Li metal as anode. The preliminary results are interesting, exhibiting good reversibility and cyclability.     

Development of gel-polymer electrolytes and nano-structured electrodes for Li-ion polymer batteries

A novel methacrylic gel-polymer membrane was synthesized by free radical photo polymerisation (UV-curing technique). The polymerisation was very easy, fast and reliable and the membrane shows good behaviour in terms of both conductivity and cyclability in Li cells. The anode materials were prepared by high energy ball milling obtaining nanocrystalline Ni–Sn alloys, while the hydrothermal processing in presence of a template was used to prepare nanostructured LiFePO₄/C as cathode material. Every component has been characterised separately from the structural and electrochemical point of view. The first experimental data on the performance of a complete Li-ion polymer cell assembled with the components studied are also presented. The results obtained demonstrate the overall satisfying, and some superior performances of the various single components and their feasibility as a complete system.     

Mesoporous carbons as low temperature fuel cell platinum catalyst supports

Platinum catalysts supported on ordered mesoporous carbons (OMC) are described. The mesoporous carbon support, CMK3 type, was synthesised as an inverse replica of a SBA-15 silica template. The platinum catalysts (i.e. Pt 20 wt% and Pt 10 wt%, respectively), obtained through a conventional wet impregnation method, have been investigated to determine their structural characteristics and electrochemical behaviour. The electro-catalytic performance towards the oxygen reduction reaction (ORR) was compared to those of commercial Pt/C-Vulcan XTC72R (E-Tek) catalysts with the same Pt wt%, under the same experimental conditions. The two catalyst samples have allowed the effect of the variation of both the Pt to Nafion and Pt to the supporting carbon ratios to be studied. Electrochemical tests have been carried out in three different systems: a catalyst ink deposited on a glassy carbon rotating disk electrode (RDE), a gas diffusion electrode (GDE) in a three-electrode cell with H₂SO₄ as the electrolyte and a complete PEM single fuel cell. The first results indicate that the OMC performs slightly less well than commercial carbon supports, mainly in the complete fuel cell system. The data from the cell tests indicate a less effective distribution of Nafion on the OMC surface which, probably, decreases the platinum utilisation and the proton conductivity.