Modification of Nafion with silica nanoparticles in supercritical carbon dioxide for electrochemical applications

Two-Dimensional MFI-Type Zeolite Flow Battery Membranes

Vanadium flow battery (VFB) is one of the most reliable stationary electrochemical energy-storage technologies, and a membrane with high vanadium resistance and proton conductivity is essential for manufacturing high-performance VFBs. In this study, a two-dimensional (2D) MFI-type zeolite membrane was fabricated from zeolite nanosheet modules, which displayed excellent vanadium resistance (0.07 mmol L-1 h-1 ) and proton conductivity (0.16 S cm-1 ), yielding a coulombic efficiency of 93.9 %, a voltage efficiency of 87.6 %, and an energy efficiency of 82.3 % at 40 mA cm-2 . The self-discharge period of a VFB equipped with 2D MFI-type zeolite membrane increased up to 116.2 h, which was significantly longer than that of the commercial perfluorinated sulfonate membrane (45.9 h). Furthermore, the corresponding battery performance remained stable over 1000 cycles (>1500 h) at 80 mA cm-2 . These findings demonstrate that 2D MFI-type membranes are promising ion-conductive membranes applicable for stationary electrochemical energy-storage devices.

Modification of the Physical Properties of a Nafion Film Due to Inclusion of n-Dodecyltriethylammonium Cation: Time Effect

This study investigates the effects of modifying commercial Nafion-212 thin films with dodecyltriethylammonium cation (DTA+) on their electrical resistance, elastic modulus, light transmission/reflection and photoluminescence properties. The films were modified through a proton/cation exchange process for immersion periods ranging from 1 to 40 h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the crystal structure and surface composition of the modified films. The electrical resistance and the different resistive contributions were determined via impedance spectroscopy. Changes in the elastic modulus were evaluated using stress-strain curves. Additionally, optical characterization tests, including light/reflection (250-2000 nm) and photoluminescence spectra, were also performed on both unmodified and DTA⁺-modified Nafion films. The results reveal significant changes in the electrical, mechanical and optical properties of the films, depending on the exchange process time. In particular, the inclusion of the DTA⁺ into the Nafion structure improved the elastic behavior of the films by significantly decreasing the Young modulus. Furthermore, the photoluminescence of the Nafion films was also enhanced. These findings can be used to optimize the exchange process time to achieve specific desired properties.

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds.

Structural and Electrotransport Properties of Perfluorinated Sulfocationic Membranes Modified by Silica and Zirconium Hydrophosphate

A correlation between changes in structural and electrotransport properties of membranes after modification by silica and zirconium hydrophosphate was established. The total water volume, volume fraction of the free water in the membrane and the volume fraction of the water having high binding energy were considered as structural characteristics, which were found from the curves of water distribution on the water binding energy and the effective pore radii. The conductivity, diffusion and electroosmotic permeabilities were investigated as electrotransport properties. The influence of the modifier type on the current flow paths in the membrane was analyzed within the framework of the extended three-wire model. It has been established that the treatment of membranes with alcohol before the intercalation of a modifier leads to the appearance of cavities with an effective size of more than 100 nm filled with free water with the binding energy less than 10 J/mol. It is accompanied with an increase in the diffusion permeability of hybrid membranes by approximately 3-6 times in NaCl and HCl solutions, which limits the application of such materials in proton exchange membrane fuel cells. The different conditions of modification of perfluorinated membranes with similar properties by the dopant with same type allow for the preparation of the hybrid materials for various applications such as electrodialysis concentration or electric current generation devices.

Organosilicone Compounds in Supercritical Carbon Dioxide

This review considers the key advantages of using supercritical carbon dioxide as a solvent for systems with organosilicon compounds. Organosilicon polymeric materials synthesis as well as the creation and modification of composites based on them are discussed. Polydimethylsiloxane and analogues used as polymerization stabilizers and nucleation promoters in pore formation processes are analyzed as well.

Janus Polymer Composite Electrolytes Improve the Cycling Performance of Lithium-Oxygen Battery

The liquid electrolytes in lithium-air (oxygen) batteries are prone to volatilize, leak, flame, and cause uneven deposition of lithium during cycling, which makes the batteries to face serious problems in terms of safety and cycling stability. A novel Janus quasi-solid composite polymer electrolyte was fabricated by perfluorosulfonic acid (Nafion) membranes with tunable thickness and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP). The Nafion membranes not only guarantee the mechanical strength of the composites but also effectively prevent the migration of certain anions and macromolecules. The results indicate that Janus quasi-solid composite polymer electrolytes have excellent thermal stability, high lithium-ion migration number, and wide electrochemical window. Lithium-oxygen batteries using the novel quasi-solid composite electrolytes perform lower polarization and better cycling stability. The excellent properties of the quasi-solid composite electrolytes make it one of the effective materials for improving the cycling stability of lithium-air (oxygen) batteries.

Non-humidified fuel cells using a deep eutectic solvent (DES) as the electrolyte within a polymer electrolyte membrane (PEM): the effect of water and counterions

In this research, deep eutectic solvents (DESs) were prepared and employed as the electrolyte in Nafion membranes. Different factors, such as the water content and Nafion counterions (H⁺, Li⁺, Na⁺ and K⁺), which could influence the PEM performance, were evaluated. The obtained results showed that the presence of water may have a constructive or destructive effect on the DES and Nafion/DES properties, which should be considered for their final applications. Also, the electronegativity of the counterion can significantly influence the Nafion/DES proton conductivity. The prepared Nafion/DES composite membranes showed superconducting properties as a result of a Grotthuss-like mechanism for proton conduction. The conductivities of the prepared membranes were compared to those of other membranes based on an upper bound concept, which showed the potential use of DESs as a promising alternative to conventional ionic liquids. Finally, the fuel cell performances of the prepared membranes at different temperatures were evaluated.