Ionic liquid dynamics in nanoporous carbon: A pore-size- and temperature-dependent neutron spectroscopy study on supercapacitor materials

Abstract

The influence of spatial confinement on the thermally excited stochastic cation dynamics of the roomtemperature ionic liquid 1-N-butylpyridinium bis-[(trifluoromethyl)sulfonyl]imide ([BuPy][Tf 2 N]) inside porous carbide-derived carbons with various pore sizes in the sub-to a few nanometer range is investigated by quasielastic neutron spectroscopy. Using the potential of fixed window scans, i.e., scanning a sample parameter, while observing solely one specific energy transfer value, an overview of the dynamic landscape within a wide temperature range is obtained. It is shown that already these data provide a quite comprehensive understanding of the confinement-induced alteration of the molecular mobility in comparison to the bulk. A complementary, more detailed analysis of full energy transfer spectra at selected temperatures reveals two translational diffusive processes on different time scales. Both are considerably slower than in the bulk liquid and show a decrease of the respective self-diffusion coefficients with decreasing nanopore size. Different thermal activation energies for molecular self-diffusion in nanoporous carbons with similar pore size indicate the importance of pore morphology on the molecular mobility, beyond the pure degree of confinement. In spite of the dynamic slowing down we can show that the temperature range of the liquid state upon nanoconfinement is remarkably extended to much lower temperatures, which is beneficial for potential technical applications of such systems.

Insight into the Electrical Double Layer of Ionic Liquids Revealed through Its Temporal Evolution

“…In the porous electrodes of supercapacitors, the confinement provided by the nanopores alters ion–ion correlations [ 52 ] and thereby the dynamics of the confined IL. [ 53 ] Therefore, it is generally accepted that the motion of the IL ions under nanoconfinement differs from that in the unconfined state. [ 54 ] This work describes the additional effects that the evolution of the nanostructure in the unconfined state has on the evolution of the confined structure.…”

Elucidating Curvature-Capacitance Relationships in Carbon-Based Supercapacitors

“…This corresponds to a classical treatment of the charge distribution in an electrode corresponding to a given applied potential and nearby electrolyte configuration, and assuming that the electrode material is a perfect metal. While experimentally, the EDL of ionic liquids has been studied by x-ray electron spectroscopy [23], quasielastic neutron scattering [24], nuclear magnetic resonance spectroscopy [25], scanning tunneling microscopy [26][27][28], and dynamic [29,30] or static [31,32] atomic force microscopy, CONP methods ultimately allow for the simulation of a variety of electrochemical systems with complex geometries, e.g., carbide-derived carbons in contact with a variety of electrolytes, such as aqueous or organic solutions, room temperature ionic liquids, and salts dissolved in water [33][34][35][36][37].…”

Dynamically disordered hydrogen bonds in the hureaulite-type phosphatic oxyhydroxide Mn5[(PO4)2(PO3(OH))2](HOH)4

“…The dynamic disorder of protons over such sites and routes represents an interesting object for both experimental and theoretical studies of complex proton behaviors. 3,[16][17][18][19][20][21][22][23] Furthermore, according to Baranov,8 hureaulite shows a high theoretical intrinsic charge carrier concentration of N p = 2.629 × 10 22 protons per cm 3 , exceeding the boundary value N p, limit = 10 18 protons cm −3 between high and low proton mobility. 24 This motivated us to resolve a consistent picture of charge transport via protons over the DDHBs in this complex system by diffraction and spectroscopy tools in combination with density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations performed with the CP2K code, as described below.…”