Electrochemical and Surface Characterization Study on the Corrosion Inhibition of Mild Steel 1030 by the Cationic Surfactant Cetrimonium Trans-4-hydroxy-cinnamate.

Effective corrosion inhibition of mild steel 1030 at 0.01 M NaCl concentration was achieved by the use of the nontoxic surfactant salt cetrimonium trans-4-hydroxy-cinnamate (CTA-4OHcinn). Polarization analysis on the steel samples immersed for 24 h in the control and CTA-4OHcinn-containing solutions shows the development of a passivation potential that is more obvious at higher inhibitor concentrations along with a maximum inhibition efficiency of 97.8%. Electrochemical impedance spectroscopy (EIS) pinpoints the effect of the inhibitor on the corroding regions of the metal surface, showing an increase in the local electric resistance and conversely a decrease in the local capacitance, which indicates that the charge transfer in the corroding regions is being hindered by a deposition process. This is consistent with scanning electron microscopy (SEM) images, showing the presence of a porous oxide matrix that fills localized corrosion sites on the metal surface after 24 h of immersion in a 0.01 M NaCl + 10 mM inhibitor solution. Additionally, SEM analysis also shows the formation of an organic film surrounding the defects that is able to shield chloride attack. As a result of diffusion of chloride from the defects below the protective film, filiform corrosion can be seen. Time-resolved impedance analysis over the first 120 min of immersion in the control and inhibitor solution shows that significant inhibitor protection does not take place immediately and there is a lag phase in the first 50 min of immersion, suggesting that early localized corrosion drives further adsorption of inhibitor micelles on the metal surface. This is in agreement with X-ray photoelectron spectroscopy (XPS) analysis, which indicates a complete surface coverage over the first 2 h of immersion in a concentrated inhibitor solution. XPS also shows the heterogeneity of the film, where some parts are poorly covered, revealing the underlying surface containing iron.

The influence of alkyl chain branching on the properties of pyrrolidinium-based ionic electrolytes.

Ionic liquids and plastic crystals based on pyrrolidinium cations are recognised for their advantageous properties such as high conductivity, low viscosity, and good electrochemical and thermal stability. The pyrrolidinium ring can be substituted with symmetric or asymmetric alkyl chain substituents to form a range of ionic liquids or plastic crystals depending on the anion. However, reports into the use of branched alkyl chains and how this influences the material properties are limited. Here, we report the synthesis of six salts - ionic liquids and organic ionic plastic crystals - where the typically used linear propyl chain substituent is replaced by the branched alternative, isopropyl, to form the cation [C(i3)mpyr]+, in combination with six different anions: dicyanamide, (fluorosulfonyl)(trifluoromethanesulfonyl)imide, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, tetrafluoroborate and hexafluorophosphate. The thermal and transport properties of these salts are compared to those of the analogous N-propyl-N-methylpyrrolidinium and N,N-diethylpyrrolidinium-based salts. Finally, a high lithium salt content ionic liquid electrolyte based on the bis(fluorosulfonyl)imide salt was developed. This electrolyte showed high coulombic efficiencies of lithium plating/stripping and high lithium ion transference number, making it a strong candidate for use in lithium metal batteries.

Organic salts utilising the hexamethylguanidinium cation: the influence of the anion on the structural, physical and thermal properties.

The synthesis and characterisation of new solid-state electrolytes is a key step in advancing the development of safer and more reliable electrochemical energy storage technologies. Organic ionic plastic crystals (OIPCs) are an increasingly promising class of material for application in devices such as lithium or sodium metal batteries as they can support high ionic conductivity, with good electrochemical and thermal stability. However, the choice of OIPC-forming ions is still relatively limited. Furthermore, understanding of the influence of different cations and anions on the thermal, structural and transport properties of these materials is still in its infancy. Here we report the synthesis and in-depth characterisation of a range of new OIPCs utilising the hexamethylguanidinium cation ([HMG]) with five different anions. The thermal, structural, transport properties and free volume in the different salts have been investigated. The free volume within the salts has been investigated by positron annihilation lifetime spectroscopy, and the single crystal and powder X-ray diffraction analysis of [HMG] bis(trifluoromethanesulfonyl)imide ([TFSI]) in phase I and II, [HMG] hexafluorophosphate ([PF6]) and [HMG] tetrafluoroborate ([HMG][BF4]) are reported. The HMG cation can exhibit significant disorder, which is advantageous for plasticity and future use of these materials as high ionic conductivity matrices. The bis(fluorosulfonyl)imide salt, [HMG][FSI], is identified as particularly promising for use as an electrolyte, with good electrochemical stability and soft mechanical properties. The findings introduce a range of new materials to the solid-state electrolyte arena, while the insights into the physico-chemical relationships in these materials will be of importance for the future development and understanding of other ionic electrolytes.

Efficient and Stable Solid-State Dye-Sensitized Solar Cells by the Combination of Phosphonium Organic Ionic Plastic Crystals with Silica.

Remarkably efficient quasi-solid-state dye-sensitized solar cells (DSSCs) have been fabricated using organic ionic plastic crystal electrolytes based on a small triethyl(methyl)phosphonium [P1222] cation and two types of sulfonamide anions, bis(fluorosulfonyl)amide (FSA) and bis(trifluoromethanesulfonyl)amide (TFSA), in combination with varying amounts of silica (SiO2). Solar cell efficiencies of up to 7.4% were obtained, which is comparable to our benchmark efficiencies of liquid (acetonitrile) electrolyte-based devices. Such a high efficiency for DSSCs using quasi-solid-state electrolytes is attributed to improved ionic conductivity, enhanced redox couple transport, improved interfacial interaction between the electrolyte and the electrode as well as decreased resistance at both electrode interfaces. Notably, the devices with the silica-containing electrolytes displayed excellent stability after 5 months of storage, with the most stable devices, formed with either plastic crystal electrolyte containing 2% silica, showing no decrease in efficiency.

A symmetrical ionic liquid/Li salt system for rapid ion transport and stable lithium electrochemistry.

Contrary to the accepted wisdom that avoids cation symmetry for the sake of optimum electrolyte properties, we reveal outstanding behaviour for the diethylpyrrolidinium cation ([C2epyr]), in combination with the bis(fluorosulfonyl)imide (FSI) anion and Li[FSI]. The equimolar [C2epyr][Li][FSI]2 is a liquid with high conductivity, high Li transference number and >90% lithium metal cycling efficiency. The high level of performance for these electrolytes invites consideration of a new class of electrolytes for lithium batteries.

Probing Ionic Liquid Electrolyte Structure via the Glassy State by Dynamic Nuclear Polarization NMR Spectroscopy.

Dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy has been used to study an ionic liquid salt solution (N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide, C3mpyrFSI, containing 1.0 m lithium bis(fluorosulfonyl)imide, 6LiFSI) in its glassy state at a temperature of 92 K. The incorporation of a biradical to enable DNP signal enhancement allowed the proximities of the lithium to the individual carbon sites on the pyrrolidinium cation to be probed using a 13C-6Li REDOR pulse sequence. Distributions in Li-C distances were extracted and converted into a 3D map of the locations of the Li+ relative to the C3mpyr that shows remarkably good agreement with a liquid-phase molecular dynamics simulation.

Synthesis and physical properties of tris(dialkylamino)cyclopropenium dicyanamide ionic liquids.

The synthesis and properties of 16 tris(dialkylamino)cyclopropenium (TDAC) cations with the dicyanamide (DCA) anion, [N(CN)2]-, are described. D 3h- and C 3h-symmetric cations ([C3(NR2)3]DCA (R = Me, Et, Pr, Bu, Pent, Hex, Dec) and [C3(NRMe)3]DCA (R = Bu, St), respectively) were synthesised by reaction of C3Cl5H with the corresponding amine. Reaction of the alkoxydiaminocyclopropenium salt [C3(NEt2)2(OMe)]+ with amines led to a series of C 2v-symmetric salts [C3(NEt2)2(NR2)]DCA (R = Me, Bu, Hex) and two C s-symmetric salts and [C3(NEt2)2(NRMe)]DCA (R = Me, Bu). Similarly, [C3(NMe2)2(OMe)]+, was used to prepare the C s-symmetric salts [C3(NMe2)2(NRMe)]DCA (R = Pr, Bu). In addition to characterisation by NMR, mass spectrometry and microanalysis, the salts were characterised by DSC, TGA, density, viscosity, conductivity and miscibility/solubility studies. Comparisons have been made with similar series of bistriflimide (NTf2 -) salts that have been previously reported to see whether the same trends are observed with a different anion.