FTIR spectroscopic investigations of supersaturated NaClO4 aerosols

Investigation of Solid Polymer Electrolytes for NASICON-Type Solid-State Symmetric Sodium-Ion Battery

The inevitable shift toward renewable energy and electrification necessitates earth-abundant sodium reserves for next-generation Na-based energy storage technologies. By coupling the benefits of solid electrolytes over traditional nonaqueous electrolytes due to their safety hazards, solid-state sodium-ion batteries hold huge prospects in the future. This work presents a comprehensively developed solid-state sodium-ion symmetric full cell operating at room temperature enabled through a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer electrolyte and modified NASICON-structured positive and negative electrodes. Among the investigated polymer electrolytes, PVDF-HFP-NaTFSI was found to outperform other counterparts by achieving a higher ionic conductivity and delivered an appreciable electrochemical stability window. By further delving into the properties of PVDF-HFP-NaTFSI, it was found to possess the least crystallinity, minimal porous structure, lowest melting point, and fusion enthalpy, indicating better ion transport than other investigated polymer electrolytes. The as-assembled solid-state battery revealed a storage capacity of 74 mAh g-1 at 0.1 C with a specific energy density of 130 Wh kgcathode_active_material-1 and demonstrated an impressive capacity retention of 84% of the initial capacity after 200 cycles. The structure and morphology retention of the cycled electrode and electrolyte through postmortem analysis bolster the electrochemo-mechanical stability of the developed solid cell. The findings reported here on polymer electrolytes persuade expedient solutions for developing ambient temperature solid-state sodium-ion batteries with promising electrochemical performance for commercialization in the near future.

Inelastic and elastic neutron scattering studies of the vibrational and reorientational dynamics, crystal structure and solid-solid phase transition in [Mn(OS(CH₃)₂)₆](ClO₄)₂ supported by theoretical (DFT) calculations

The vibrational and reorientational dynamics of CH3 groups from (CH3)2SO ligands in the high- and low-temperature phases of [Mn(OS(CH3)2)6](ClO4)2 were investigated by quasielastic and inelastic incoherent neutron scattering (QENS and IINS) methods. The results show that above the phase transition temperature (detected earlier by differential scanning calorimetry (DSC) at TC5(c)=222.9K on cooling and at TC5(h)=225.4K on heating) the CH3 groups perform fast (τR≈10(-12)-10(-13)s) reorientational motions. These motions start to slow down below TC5(c) Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS and IINS, indicated that this phase transition is associated with a change of the crystal structure, too. Theoretical infrared absorption, Raman and inelastic incoherent neutron scattering spectra were calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on C, H, S, O atoms) for the isolated equilibrium model (isolated [Mn(DMSO)6](2+) cation and ClO4(-) anion). Calculated spectra show a good agreement with the experimental spectra (FT-IR, RS and IINS). The comparison of the results obtained by these complementary methods was made.

Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations

The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ρr(NH3) and νas(N-H) modes, respectively, indicate that there exist fast (correlation times τR≈10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6](2+) cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models.

Effect of hygroscopicity of the metal salt on the formation and air stability of lyotropic liquid crystalline mesophases in hydrated salt-surfactant systems

It is known that alkali, transition metal and lanthanide salts can form lyotropic liquid crystalline (LLC) mesophases with non-ionic surfactants (such as CiH2i+1(OCH2CH2)jOH, denoted as CiEj). Here we combine several salt systems and show that the percent deliquescence relative humidity (%DRH) value of a salt is the determining parameter in the formation and stability of the mesophases and that the other parameters are secondary and less significant. Accordingly, salts can be divided into 3 categories: Type I salts (such as LiCl, LiBr, LiI, LiNO3, LiClO4, CaCl2, Ca(NO3)2, MgCl2, and some transition metal nitrates) have low %DRH and form stable salt-surfactant LLC mesophases in the presence of a small amount of water, type II salts (such as some sodium and potassium salts) that are moderately hygroscopic form disordered stable mesophases, and type III salts that have high %DRH values, do not form stable LLC mesophases and leach out salt crystals. To illustrate this effect, a large group of salts from alkali and alkaline earth metals were investigated using XRD, POM, FTIR, and Raman techniques. Among the different salts investigated in this study, the LiX (where X is Cl(-), Br(-), I(-), NO3(-), and ClO4(-)) and CaX2 (X is Cl(-), and NO3(-)) salts were more prone to establish LLC mesophases because of their lower %DRH values. The phase behavior with respect to concentration, stability, and thermal behavior of Li(I) systems were investigated further. It is seen that the phase transitions among different anions in the Li(I) systems follow the Hofmeister series.

Magnesium Sulfate Aerosols Studied by FTIR Spectroscopy: Hygroscopic Properties, Supersaturated Structures, and Implications for Seawater Aerosols

Supersaturated MgSO4 aerosols and dilute MgSO4 solutions were studied by FTIR spectroscopic techniques (i.e., aerosol flow tube (AFT) and attenuated total reflection (ATR)). The hygroscopic properties of MgSO4 aerosols were investigated with results in good agreement with previous measurements by a scanning electrodynamic balance (SEDB). Well-defined spectral evolutions with changing relative humidity (RH) for the v3 band of SO4(2-) and the water O-H stretching envelope could be directly related to the observed hygroscopic properties of MgSO4 aerosols. When the RH decreased from approximately 55 to approximately 40%, the v1 band of SO4(2-) in supersaturated MgSO4 aerosols was observed to transform from a sharp peak at approximately 983 cm(-1) into a wide band at approximately 1005 cm(-1). The sharp peak at approximately 983 cm(-1) was mainly assigned to such associated complexes of Mg2+ and SO4(2-) as double solvent-separated ion pairs (2SIPs), solvent-shared ion pairs (SIPs), and simple contact ion pairs (CIPs) in supersaturated MgSO4 aerosols, while the wide band at approximately 1005 cm(-1) was due to polymeric CIPs chains, probably the main component of gels formed in MgSO4 aerosols at low RHs. Relating to this v1 band transformation, the peak position of the v(3) band was first shown to be a sensitive indicator of CIPs formation, spanning across approximately 40 cm(-1) on the formation of polymeric CIPs chains, which could also be supported by aerosol composition analysis in the form of water-to-solute molar ratios (WSR). In the water O-H stretching envelope, the absorbance intensities at 3371 and 3251 cm(-1) were selected to represent contributions from weak and strong hydrogen bonds, respectively. The absorbance intensity ratio changing with RH of 3371 to 3251 cm(-1) could be related to the previous observations with the v1 and v3 bands of SO4(2-). As a result, the formation of CIPs with various structures in large amounts was supposed to significantly weaken hydrogen bonds in supersaturated MgSO4 aerosols, while 2SIPs and SIPs were not expected to have similar effects even when occurring in abundance. In comparison with MgSO4 aerosols, the peak positions of the v3 band of SO4(2-) in artificial seawater aerosols implied that the MgSO4 component should be contained as gels or concentrated solutions in the fissures of microcrystals of sea salts for freshly formed seawater aerosols at low RHs.