Anomalously Enhanced Hydration of Aqueous Electrolyte Solution in Hydrophobic Carbon Nanotubes to Maintain Stability

Abstract

An understanding of the structure and behavior of electrolyte solutions in nanoenvironements is crucial not only for a wide variety of applications, but also for the development of physical, chemical, and biological processes. We demonstrate the structure and stability of electrolyte in carbon nanotubes using hybrid reverse Monte Carlo simulations of X-ray diffraction patterns. Hydrogen bonds between water are adequately formed in carbon nanotubes, although some hydrogen bonds are restricted by the interfaces of carbon nanotubes. The hydrogen bonding network of water in electrolyte in the carbon nanotubes is further weakened. On the other hand, formation of the ion hydration shell is significantly enhanced in the electrolyte in the carbon nanotubes in comparison to ion hydration in bulk electrolyte. The significant hydrogen bond and hydration shell formation are a result of gaining stability in the hydrophobic nanoenvironment.

Water Assistance in Ion Transfer during Charge and Discharge Cycles

“…18,46,50,51 Although the different parameters produced somewhat different physical properties, the above potential parameters also described experimental properties such as structures well. Furthermore, our preceding studies indicated that the structures of electrolyte and water in confined carbon nanopores using the CEMC simulations agreed well with the experimental structures, 38,52 although the comparison of dynamic properties has been inadequate. In this study, a simple point charge model was adopted to evaluate dynamic properties of electrolytes.…”

“…This indicates that the extent of hydrogen bonding was significantly decreased for those water molecules involved in hydration shell formation. 37,38 The hydrogen bonding numbers recovered to the overall average value at the charge-reversal processes. This indicated that hydration shell water molecules reformed their hydrogen bonding network just before release from the hydration shell.…”

“…Significant desolvation was imposed in extremely narrow nanopores smaller than the solvated ion size, providing an anomalous increase in capacitance. ,, In such narrow nanopores, the solvation structure was more ordered than that in wider nanopores. , Levi et al showed the direct evaluation of solvation numbers during cyclic voltammetry of electrolytes confined in carbon nanopores using a quartz crystal microbalance, and significant desolvation was seen . The desolvation in carbon nanopores was investigated using Monte Carlo and molecular dynamics (MD) simulations. ,, We observed an enhancement in hydration shell formation in carbon nanopores despite the dehydration. , On the other hand, hydration structure was retained in the LiCl aqueous solution in slit nanopores of 0.9–1.5 nm . The dynamics of ions in ionic liquids and electrolytes became slower with decreasing nanopore size. , Kalluri proposed that nanopores composed of charged graphene layers concentrated oppositely charged ions. , …”

“…32,34,36 We observed an enhancement in hydration shell formation in carbon nanopores despite the dehydration. 37,38 On the other hand, hydration structure was retained in the LiCl aqueous solution in slit nanopores of 0.9−1.5 nm. 39 The dynamics of ions in ionic liquids and electrolytes became slower with decreasing nanopore size.…”

Recent Development of Carbon Nanotube Transparent Conductive Films

“…CNTs are only at the liquid–air interface, which is the major difference from the dip-coating method. By making full use of the hydrophobicity of CNT, − thickness control of the CNT is possible by matching the target substrate surface chemistry . By repeated dipping, lifting, and drying, >100 layers can be put on quartz or glass substrates.…”