Search Results (23)

Carbon nanotube (CNT) fiber research focuses on developing functional fabrics with dual or multifunctional capabilities. This study investigates CNT fibers fabricated via dielectrophoresis (DEP) with the incorporation of 10 wt.% carbide-derived carbon (CDC), referred to as CNTCDC fibers. The linear actuation behavior of the CNT and the CNTCDC fibers is compared using identical electrolyte concentrations in both a polar aprotic solvent (propylene carbonate, PC) and a polar protic solvent (aqueous solution, aq). Electromechanical deformation (EMD) is studied through cyclic voltammetry and chronoamperometry. The CNTCDC fiber outperformed the pristine CNT fiber, exhibiting primary expansion during discharge in PC (stress: 1.64 kPa, strain: 0.1%) and during charge in water (stress: 1.32 kPa, strain: 0.047%). By contrast, the pristine CNT fibers showed mixed actuation responses in both solvents, resulting in diminished net stress and strain. Chronopotentiometric measurements indicated that the CNTCDC fibers achieved their highest specific capacitance in aqueous media, reaching 223 ± 17 F g⁻¹ at ±0.8 A g⁻¹, with a capacity retention of 94.2% at ±32 A g⁻¹. Fundamental characterization techniques, including scanning electron microcopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy, are employed to analyze fiber morphology and composition. The dual functionality of CNTCDC fibers, as both actuators and energy storage elements, is demonstrated. Full article

Nafion^® is a cation exchange polymer that is commonly used in aqueous energy applications such as fuel cells due to its ability to exclude anions and neutral molecules and increase apparent diffusion of cationic redox molecules. However, this behavior is not well studied in nonaqueous solutions. The behavior of platinum electrodes modified with recast Nafion^® films in nonaqueous solutions was observed to be different from its well-studied behavior in aqueous solutions. The reversible redox couple tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate was studied in the nonaqueous, aprotic solvent acetonitrile with different electrolytes (tetrabutylammonium tetrafluoroborate, tetrabutylammonium trifluoromethanesulfonate, tetrabutylammonium hexafluorophosphate, and ammonium trifluoromethanesulfonate) using cyclic voltammetry and rotating disk voltammetry. An unmodified platinum electrode in the nonaqueous systems and a recast Nafion^®-modified platinum electrode equilibrated in an aqueous solution of tris(bipyridine)ruthenium(II)chloride hexahydrate were used as controls. Results indicate that the polymer structure in acetonitrile conditions does not allow apparent (Dahms–Ruff) diffusion but does allow significant physical diffusion that would make Nafion a great immobilization option for modifying electrodes with catalysts in nonaqueous systems. Full article

Electrochemical behavior of novel electrode materials based on polydiphenylamine-2-carboxylic acid (PDPAC) binary and ternary nanocomposite coatings was studied for the first time. Nanocomposite materials were obtained in acidic or alkaline media using oxidative polymerization of diphenylamine-2-carboxylic acid (DPAC) in the presence of activated IR-pyrolyzed polyacrylonitrile (IR-PAN-a) only or IR-PAN-a and single-walled carbon nanotubes (SWCNT). Hybrid electrodes are electroactive layers of stable suspensions of IR-PAN-a/PDPAC and IR-PAN-a/SWCNT/PDPAC nanocomposites in formic acid (FA) formed on the flexible strips of anodized graphite foil (AGF). Specific capacitances of electrodes depend on the method for the production of electroactive coatings. Electrodes specific surface capacitances C_s reach 0.129 and 0.161 F∙cm⁻² for AGF/IR-PAN-a/PDPAC_ac and AGF/IR-PAN-a/SWCNT/PDPAC_ac, while for AGF/IR-PAN-a/PDPAC_alk and AGF/IR-PAN-a/SWCNT/PDPAC_alk C_s amount to 0.135 and 0.151 F∙cm⁻². Specific weight capacitances C_w of electrodes with ternary coatings reach 394, 283, 180 F∙g⁻¹ (AGF/IR-PAN-a/SWCNT/PDPAC_ac) and 361, 239, 142 F∙g⁻¹ (AGF/IR-PAN-a/SWCNT/PDPAC_alk) at 0.5, 1.5, 3.0 mA·cm⁻² in an aprotic electrolyte. Such hybrid electrodes with electroactive nanocomposite coatings are promising as a cathode material for SCs. Full article

The electrochemical behavior of new electrode materials based on poly-N-phenylanthranilic acid (P-N-PAA) composites with reduced graphene oxide (RGO) was studied for the first time. Two methods of obtaining RGO/P-N-PAA composites were suggested. Hybrid materials were synthesized via in situ oxidative polymerization of N-phenylanthranilic acid (N-PAA) in the presence of graphene oxide (GO) (RGO/P-N-PAA-1), as well as from a P-N-PAA solution in DMF containing GO (RGO/P-N-PAA-2). GO post-reduction in the RGO/P-N-PAA composites was carried out under IR heating. Hybrid electrodes are electroactive layers of RGO/P-N-PAA composites stable suspensions in formic acid (FA) deposited on the glassy carbon (GC) and anodized graphite foil (AGF) surfaces. The roughened surface of the AGF flexible strips provides good adhesion of the electroactive coatings. Specific electrochemical capacitances of AGF-based electrodes depend on the method for the production of electroactive coatings and reach 268, 184, 111 F∙g⁻¹ (RGO/P-N-PAA-1) and 407, 321, 255 F∙g⁻¹ (RGO/P-N-PAA-2.1) at 0.5, 1.5, 3.0 mA·cm⁻² in an aprotic electrolyte. Specific weight capacitance values of IR-heated composite coatings decrease as compared to capacitance values of primer coatings and amount to 216, 145, 78 F∙g⁻¹ (RGO/P-N-PAA-1_IR) and 377, 291, 200 F∙g⁻¹ (RGO/P-N-PAA-2.1_IR). With a decrease in the weight of the applied coating, the specific electrochemical capacitance of the electrodes increases to 752, 524, 329 F∙g⁻¹ (AGF/RGO/P-N-PAA-2.1) and 691, 455, 255 F∙g⁻¹ (AGF/RGO/P-N-PAA-1_IR). Full article

The objective of this work was to study the electrochemical behavior of AB₅ alloy and its composite with Pd nanoparticles in selected ionic liquids. The protic ionic liquid (diethylmethylammonium triflate) and the mixture of aprotic ionic liquid (1-ethyl-3-methylimidazolium methanesulfonate) with parent superacid were used as electrolytes in the process of hydrogen electrosorption in AB₅ alloy electrodes. The impact of the surface modification of AB₅ electrode with Pd nanoparticles has been checked. The studies revealed that the highest hydrogen absorption capacity can be obtained in Pd-NPs-AB₅ electrode in DEMA-TFO. It was found that the surface modification with Pd-NPs facilitates the activation of the electrode and results in stabilization of the plateau potential of discharging. The studies show that more effort should be put into the synthesis of less corrosive tailored ionic liquids suitable to be used as electrolytes in hydride batteries. Full article

The article considers the effect of the solvate environment of the lithium cation in various aprotic solvents.The redox reactions of electrodes made from a polymeric condensation product of triquinoyl with 1,2,4,5-tetraaminobenzene are studied. A 1 M LiPF₆ solution was used as an electrolyte, in either ethylene carbonate/dimethyl carbonate (EC/DMC) or tetraglyme. Based on the electrochemical studies and quantum chemical modeling, it was shown that the desolvation of lithium cations in the tetraglyme-based electrolyte makes it possible to obtain a capacity close to the theoretical one (up to 546 mAh g⁻¹) and only 125 mAh g⁻¹ for the EC/DMC electrolyte. This decrease is due to the fact that the lithium cation adds to the functional groups of the organic material with two dimethyl carbonate molecules, as well as the PF₆⁻ anion. Full article

The development of post-lithium current sources, such as sodium-ion batteries with improved energy characteristics and an increased level of safety, is one of the key issues of modern energy. It requires the search and study of materials (including electrolytes) for these devices. Polyelectrolytes with unipolar cationic conductivity based on Nafion^® membranes are promising. In this work, the effect of swelling conditions of the Nafion^® 115 membrane in Na⁺-form with mixtures of aprotic solvents such as ethylene carbonate and sulfolane on its physicochemical and electrotransport properties was studied. Nafion-Na⁺ membranes were swollen in a mixture of solvents at temperatures of 40, 60, and 80 °C. The results were obtained using methods of impedance spectroscopy, simultaneous thermal analysis, and IR spectroscopy. The best conductivity was observed for a membrane swelling at 80 °C in a mixture with a mass fraction of ethylene carbonate of 0.5, which reaches 10⁻⁴ S cm⁻¹ at 30 °C and retains rather high values down to −60 °C (10⁻⁶ S cm⁻¹). Thus, it is possible to expand the operating temperature range of a sodium battery by varying the composition of the polymer electrolyte and the conditions for its preparation. Full article

Here, we study an effect of FEC addition to TC-E918 electrolyte on the electrochemical performance of Si/C negative electrodes. The anodes were fabricated from nanosilicon powder coated with a carbon shell by means of a standard slurry technique. The low-temperature reduction of fluorocarbon on the surface of Si nanoparticles was used to form the shell. It was shown that the presence of FEC in the electrolyte increases the cyclic stability of the electrodes and maintains a 1.5-fold higher discharge capacity during 300 cycles. Impedance measurements were used to study changes in the electrode parameters during long-term cycling with and without FEC additives. Full article

Protic ionic liquids are promising electrolytes for fuel cell applications. They would allow for an increase in operation temperatures to more than 100 °C, facilitating water and heat management and, thus, increasing overall efficiency. As ionic liquids consist of bulky charged molecules, the structure of the electric double layer significantly differs from that of aqueous electrolytes. In order to elucidate the nanoscale structure of the electrolyte–electrode interface, we employ atomic force spectroscopy, in conjunction with theoretical modeling using molecular dynamics. Investigations of the low-acidic protic ionic liquid diethylmethylammonium triflate, in contact with a platinum (100) single crystal, reveal a layered structure consisting of alternating anion and cation layers at the interface, as already described for aprotic ionic liquids. The structured double layer depends on the applied electrode potential and extends several nanometers into the liquid, whereby the stiffness decreases with increasing distance from the interface. The presence of water distorts the layering, which, in turn, significantly changes the system’s electrochemical performance. Our results indicate that for low-acidic ionic liquids, a careful adjustment of the water content is needed in order to enhance the proton transport to and from the catalytic electrode. Full article

Widening the working voltage of lithium-ion batteries is considered as an effective strategy to improve their energy density. However, the decomposition of conventional aprotic electrolytes at high voltage greatly impedes the success until the presence of high concentration electrolytes (HCEs) and the resultant localized HCEs (LHCEs). The unique solvated structure of HCEs/LHCEs endows the involved solvent with enhanced endurance toward high voltage while the LHCEs can simultaneously possess the decent viscosity for sufficient wettability to porous electrodes and separator. Nowadays, most LHCEs use LiFSI/LiTFSI as the salts and β-hydrofluoroethers as the counter solvents due to their good compatibility, yet the LHCE formula of cheap LiPF₆ and high antioxidant α-hydrofluoroethers is seldom investigated. Here, we report a unique formula with 3 mol L⁻¹ LiPF₆ in mixed carbonate solvents and a counter solvent α-substituted fluorine compound (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether). Compared to a conventional electrolyte, this formula enables dramatic improvement in the cycling performance of LiCoO₂//graphite cells from approximately 150 cycles to 1000 cycles within the range of 2.9 to 4.5 V at 0.5 C. This work provides a new choice and scope to design functional LHCEs for high voltage systems. Full article

Polymerized ionic liquids (PILs) are interesting new materials in sustainable technologies for energy storage and for gas sensor devices, and they provide high ion conductivity as solid polymer electrolytes in batteries. We introduce here the effect of polar protic (aqueous) and polar aprotic (propylene carbonate, PC) electrolytes, with the same concentration of lithium bis(trifluoromethane) sulfonimide (LiTFSI) on hydrophobic PIL films. Cyclic voltammetry, scanning ionic conductance microscopy and square wave voltammetry were performed, revealing that the PIL films had better electroactivity in the aqueous electrolyte and three times higher ion conductivity was obtained from electrochemical impedance spectroscopy measurements. Their energy storage capability was investigated with chronopotentiometric measurements, and it revealed 1.6 times higher specific capacitance in the aqueous electrolyte as well as novel sensor properties regarding the applied solvents. The PIL films were characterized with scanning electron microscopy, energy dispersive X-ray, FTIR and solid state nuclear magnetic resonance spectroscopy. Full article

The conduction of protons and other ions in nanoporous materials, such as metal-organic frameworks (MOFs), is intensively explored with the aim of enhancing the performance of energy-related electrochemical systems. The ionic conductivity, as a key property of the material, is typically determined by using electrochemical impedance spectroscopy (EIS) in connection with a suitable equivalent circuit. Often, equivalent circuits are used where the physical meaning of each component is debatable. Here, we present an equivalent circuit for the ionic conduction of electrolytes in nanoporous, nonconducting materials between inert and impermeable electrodes without faradaic electrode reactions. We show the equivalent circuit perfectly describes the impedance spectra measured for the ion conduction in MOFs in the form of powders pressed into pellets as well as for MOF thin films. This is demonstrated for the ionic conduction of an aprotic ionic liquid, and of various protic solvents in different MOF structures. Due to the clear physical meaning of each element of the equivalent circuit, further insights into the electrical double layer forming at the MOF-electrode interface can be obtained. As a result, EIS combined with the appropriate reference circuit allows us to make statements of the quality of the MOF-substrate interface of different MOF-film samples. Full article

One of the main challenges to combat climate change is to eliminate or reuse Carbon dioxide (CO₂), the largest contributor to the greenhouse gases that cause global warming. It is also important to synthesize compounds through greener technologies in order to obtain more environmentally friendly solutions. This study describes the electrocarboxylation process of α,α,α-trifluorotoluene using different working electrodes (glassy carbon, silver and copper) and electrolytes (polar aprotic solvent and ionic liquid). Carboxylated compounds were obtained in the same way in both electrolytic medias with more than 80% conversion rates, high yields, good selectivity, and moderate efficiencies using silver and copper as cathodes in organic electrolytes and ionic liquids. Full article

The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10⁻⁴ S cm⁻¹ demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications. Full article

In this manuscript, we report a detailed physico-chemical comparison between the α- and β-polymorphs of the NaMnO₂ compound, a promising material for application in positive electrodes for secondary aprotic sodium batteries. In particular, the structure and vibrational properties, as well as electrochemical performance in sodium batteries, are compared to highlight differences and similarities. We exploit both laboratory techniques (Raman spectroscopy, electrochemical methods) and synchrotron radiation experiments (Fast-Fourier Transform Infrared spectroscopy, and X-ray diffraction). Notably the vibrational spectra of these phases are here reported for the first time in the literature as well as the detailed structural analysis from diffraction data. DFT+U calculations predict both phases to have similar electronic features, with structural parameters consistent with the experimental counterparts. The experimental evidence of antisite defects in the beta-phase between sodium and manganese ions is noticeable. Both polymorphs have been also tested in aprotic batteries by comparing the impact of different liquid electrolytes on the ability to de-intercalated/intercalate sodium ions. Overall, the monoclinic α-NaMnO₂ shows larger reversible capacity exceeding 175 mAhg⁻¹ at 10 mAg⁻¹. Full article