Specific ion effects at graphitic interfaces

Abstract

Improved understanding of aqueous solutions at graphitic interfaces is critical for energy storage and water desalination. However, many mechanistic details remain unclear, including how interfacial structure and response are dictated by intrinsic properties of solvated ions under applied voltage. In this work, we combine hybrid first-principles/continuum simulations with electrochemical measurements to investigate adsorption of several alkali-metal cations at the interface with graphene and within graphene slit-pores. We confirm that adsorption energy increases with ionic radius, while being highly dependent on the pore size. In addition, in contrast with conventional electrochemical models, we find that interfacial charge transfer contributes non-negligibly to this interaction and can be further enhanced by confinement. We conclude that the measured interfacial capacitance trends result from a complex interplay between voltage, confinement, and specific ion effects-including ion hydration and charge transfer.

Water-ion permselectivity of narrow-diameter carbon nanotubes

“…S8). The result indicates that the inclusion of polarization effects beyond a simple point-charge approximation that is often used in force field simulations is important for an accurate estimate of the activation energy of ion permeation through CNTPs ( 33 ).…”

“…Here, the water molecule and chloride ion, as well as the CNTP, were explicitly described using DFT with the van der Waals density functional (vdW-DF2) ( 53 ). As discussed in our previous study ( 33 ), the hybrid quantum-continuum approach goes beyond a simple point-charge approximation that is often used in conventional classical simulations, thereby providing a more realistic description of the water-CNTP and ion-CNTP interactions. In these calculations, ultrasoft pseudopotentials were used for the description of the interaction between valence electrons and ionic cores ( 54 ); in addition, the electronic wave function and charge density were expanded in a plane-wave basis set truncated at the cutoff energies of 40 and 320 rydberg, respectively.…”

Intrapore energy barriers govern ion transport and selectivity of desalination membranes

“…Our computational method is based on a newly developed hybrid quantum-continuum technique that combines the Kohn-Sham DFT with the effective screening medium (ESM) ( 62 , 63 ) and reference interaction site model (RISM) ( 64 ), known as ESM-RISM. This approach has been successfully applied to solve the complex electrochemical interface under confinement effects ( 65 , 66 ). The DFT calculation with ESM-RISM was carried out by the Quantum ESPRESSO software ( 67 ).…”

Nanoporous carbon for electrochemical capacitive energy storage

“…[261][262][263] Classic DFT and molecular DFT (MDFT) can be used to calculate the free energy of solvent which is very useful information while discussing the desolvation of ions, especially for aqueous and organic electrolyte systems, confined in nanopores. [264][265][266][267][268][269][270][271][272][273] Following on, we will introduce in the next section a few simulation methods which are frequently used for modeling the ion confinement in nanopores, starting with Monte Carle simulations.…”