Ion Charge Density Research Articles

Cellulose Nanocrystals' Assembly under Ionic Strength Variation: From High Orientation Ordering to a Random Orientation.

We discuss the effect of the ionic strength and effective charge density on the final structural organization of cellulose nanocrystals (CNCs) after drying suspensions with different ionic strengths in terms of quantitative characteristics of the orientation order, rarely considered to date. We observed that increasing the ionic strength in the initial suspension results in continuous shrinking of the helical pitch length that shifts the photonic band gap to a far UV region from the visible range (from 400 to 250 nm) because of the increase in the helical twisting power from 4 to 6 μm-1 and doubling of the twisting angle between neighboring monolayers from 5.5 to 9°. As our estimation of the Coulombic interactions demonstrates, the reduction of the Debye charge screening length below a critical value of 3 nm results in the loss of the long-range helicoidal order and the transition to a disordered morphology with random packing of nanocrystals. Subsequently, very high orientation ordering with the 2D orientation factor, S, within the range 0.8-0.9, close to the theoretical limit of 1, gradually decreased to a very low value of S = 0.1-0.2, a characteristic of random organization at high ionic strength. We suggest that the loss of the chiral ordering is a result of the reduction of repulsive forces, promoting direct physical contact with the reduced contact area during Brownian motion, combined with increased repulsive Coulombic interactions of nanocrystals at nonparallel local packing. Notably, electrolyte addition enhances chiral interactions to the point where the helical twisting power is too large and the resulting nanocrystal bundles can no longer compactly pack without creating unfavorably large free volume. We propose that the Debye charge screening length in suspensions can be used as a universal parameter for CNCs under different conditions and can be used to assess expected ordering characteristics in the solid films.

Mixed Ionic-Electronic Conduction, a Multifunctional Property in Organic Conductors.

Organic mixed ionic-electronic conductors (OMIECs) have gained recent interest and rapid development due to their versatility in diverse applications ranging from sensing, actuation and computation to energy harvesting/storage, and information transfer. Their multifunctional properties arise from their ability to simultaneously participate in redox reactions as well as modulation of ionic and electronic charge density throughout the bulk of the material. Most importantly, the ability to access charge states with deep modulation through a large extent of its density of states and physical volume of the material enables OMIEC-based devices to display exciting new characteristics and opens up new degrees of freedom in device design. Leveraging the infinite possibilities of the organic synthetic toolbox, this perspective highlights several chemical and structural design approaches to modify OMIECs' properties important in device applications such as electronic and ionic conductivity, color, modulus, etc. Additionally, the ability for OMIECs to respond to external stimuli and transduce signals to myriad types of outputs has accelerated their development in smart systems. This perspective further illustrates how various stimuli such as electrical, chemical, and optical inputs fundamentally change OMIECs' properties dynamically and how these changes can be utilized in device applications.

Charge Storage Behaviour of α‐MoO3 in Aqueous Electrolytes – Effect of Charge Density of Electrolyte Cations

AbstractIn this paper, we show that the electrochemical performance of α‐MoO3 electrode is significantly dependent on the charge density of three studied aqueous electrolyte cations, i. e. Na+, Mg2+ and Al3+. The charge storage capacity of the α‐MoO3 electrode increases with increasing cation charge density. On the other hand, the initial coulombic efficiency decreases, and the charge transport kinetics are slowed with increasing charge density. This study provides an insightful understanding of the relationship between the charge density of metal ions and their electrochemical behaviour towards α‐MoO3 electrode in aqueous solutions. It also highlights the importance of the appropriate selection of aqueous electrolytes for enhancing electrochemical performance.

Relationship between ion vacancy mobility and hysteresis of perovskite solar cells

The relation between ion vacancy mobility and hysteresis of perovskite solar cells (PSCs) is investigated by computer simulation. Due to the ion vacancy migration, the hysteresis in PSCs strongly depends on the scan rate of J-V sweeps. The hysteresis only occurs in certain regime of scan rate. We calculate the evolution of ionic charge density stored within the Debye layers to discuss the process of ion vacancy migration and the variation of ion vacancy accumulation during the J-V sweeps. Based on this discussion, we give the physical picture of hysteresis. We discover that the regime of scan rate where hysteresis shows up moves towards higher value with increasing mobility of ion vacancy.

Adsorption of metal ions on graphene sheet for applications in environmental sensing and wastewater treatment

Experimental and computational studies showed that metal ion binding to graphene nanosheets involves a new mechanism of the interaction, ion-graphene charge transfer. Surprisingly, highly acidic= ions showed the highest affinity and ion-induced dipole appears to play a very important role in this interaction. Aqueous suspensions of graphene nanosheets (not graphene oxide or reduced graphene) were prepared by bovine serum albumin-assisted exfoliation (biographene) and metal ion binding carried out by optical spectroscopy, zeta potential analysis and Raman data. In DFT computational studies, the interactions of metal ions with graphene sheets of 20 Å × 12 Å (containing 46 carbon atoms) were examined. Interactions of the alkali and alkali earth metals were examined by M026x theory with 6–31 g basis set and d3 dispersion, while those of the transition metal systems have been examined by B3LYP theory with LanL2DZ basis set. The basis set superimposition errors were avoided using counterpoise calculations. The computed complexation energies (∆EAdsorption) were compared with the experimental values. These studies showed strong correlation of binding energies with the metal ion wlwctronegativity and charge density wkwxr, involving charge transfer between the metal ion and graphene. These surprising results imply a significant role for ion and ion-induced dipole interactions as a possible guiding factor in predicting metal ion binding affinities. A new hypothesis that charge transfer from the graphene π-cloud to the metal ion contributes to thπe binding free energy is proposed. Graphene is a strong candidate, therefore, for detecting and adsorbing metal ions from wastewater streams for sensing and environmental applications.

Characterization of Acetonitrile Isotopologues as Vibrational Probes of Electrolytes.

Acetonitrile has emerged as a solvent candidate for novel electrolyte formulations in metal-ion batteries and supercapacitors. It features a bright local C≡N stretch vibrational mode whose infrared (IR) signature is sensitive to battery-relevant cations (Li+, Mg2+, Zn2+, Ca2+) both in pure form and in the presence of water admixture across a full possible range of concentrations from the dilute to the superconcentrated regime. Stationary and time-resolved IR spectroscopy thus emerges as a natural tool to study site-specific intermolecular interactions from the solvent perspective without introducing an extrinsic probe that perturbs solution morphology and may not represent the intrinsic dynamics in these electrolytes. The metal-coordinated acetonitrile, water-separated metal–acetonitrile pair, and free solvent each have a distinct vibrational signature that allows their unambiguous differentiation. The IR band frequency of the metal-coordinated acetonitrile depends on the ion charge density. To study the ion transport dynamics, it is necessary to differentiate energy-transfer processes from structural interconversions in these electrolytes. Isotope labeling the solvent is a necessary prerequisite to separate these processes. We discuss the design principles and choice of the CD313CN label and characterize its vibrational spectroscopy in these electrolytes. The Fermi resonance between 13C≡N and C–D stretches complicates the spectral response but does not prevent its effective utilization. Time-resolved two-dimensional (2D) IR spectroscopy can be performed on a mixture of acetonitrile isotopologues and much can be learned about the structural dynamics of various species in these formulations.

In Situ Grown Co-Based Interstitial Compounds: Non-3d Metal and Non-Metal Dual Modulation Boosts Alkaline and Acidic Hydrogen Electrocatalysis.

Interfacial engineering and elemental doping are the two parameters to enhance the catalytic behavior of cobalt nitrides for the alkaline hydrogen evolution reaction (HER). However, simultaneously combining these two parameters to improve the HER catalytic properties of cobalt nitrides in alkaline media is rarely reported and also remains challenging in acidic media. Herein, it is demonstrated that high-valence non-3d metal and non-metal integration can simultaneously achieve Co-based nitride/oxide interstitial compound phase boundaries on stainless steel mesh (denoted Mo-Co5.47 N/N-CoO) for efficient HER in alkaline and acidic media. Density functional theory (DFT) calculations show that the unique structure does not only realize multi-active sites, enhanced water dissociation kinetics, and low hydrogen adsorption free energy in alkaline media, but also enhances the positive charge density of hydrogen ions (H+ ) to effectively allow H+ to receive electrons from the catalysts surface toward promoting the HER in acidic media. As a result, the as-prepared Mo-Co5.47 N/N-CoO demands HER overpotential of -28mV@10mAcm-2 in an alkaline medium, and superior to the commercial Pt/C at a current density >44mAcm-2 in acidic medium. This work paves a useful strategy to design efficient cobalt-based electrocatalysts for HER and beyond.

Design of a high-performance ternary LDHs containing Ni, Co and Mn for arsenate removal

To cope with the current serious arsenate pollution problem, a new ternary layered double hydroxides (LDHs) containing Ni, Co and Mn with good performance was developed, guiding by DFT calculations. First, Ni, Co and Mn were screened as the metal sources to constitute the LDHs, due to their high ionic charge density. Then, Ni(II), Co(II) and Mn(III)-O octahedra were selected as the primary units for structuring the LDHs, because of their good chemical activity. Meanwhile, the ratio of metals in the ternary LDHs, favoring for arsenate removal, was optimized at 1:2:1. In addition, the synergistic effect among various metals in the LDHs was considered. The results suggested that in the case of single doping, all three metals can act as the center to promote chemical activity independently. On the contrary, when combined together, there is only one unilateral active center. Moreover, the existence of ligand covalent bonds between arsenate and LDHs was confirmed. Finally, a promising new NiCo2Mn-LDHs with the maximum adsorption capacity of 407.23 mg/g for arsenate removal had been prepared.

Bridging Structure, Dynamics, and Thermodynamics: An Example Study on Aqueous Potassium Halides.

Aqueous salt systems are ubiquitous in all areas of life. The ions in these solutions impose important structural and dynamic perturbations to water. In this study, we employ a combined neutron scattering, nuclear magnetic resonance, and computational modeling approach to deconstruct ion-specific perturbations to water structure and dynamics and shed light on the molecular origins of bulk thermodynamic properties of the solutions. Our approach uses the atomistic scale resolution offered to us by neutron scattering and computational modeling to investigate how the properties of particular short-ranged microenvironments within aqueous systems can be related to bulk properties of the system. We find that by considering only the water molecules in the first hydration shell of the ions that the enthalpy of hydration can be determined. We also quantify the range over which ions perturb water structure by calculating the average enthalpic interaction between a central halide anion and the surrounding water molecules as a function of distance and find that the favorable anion-water enthalpic interactions only extend to ∼4 Å. We further validate this by showing that ions induce structure in their solvating water molecules by examining the distribution of dipole angles in the first hydration shell of the ions but that this perturbation does not extend into the bulk water. We then use these structural findings to justify mathematical models that allow us to examine perturbations to rotational and diffusive dynamics in the first hydration shell around the potassium halide ions from NMR measurements. This shows that as one moves down the halide series from fluorine to iodine, and ionic charge density is therefore reduced, that the enthalpy of hydration becomes less negative. The first hydration shell also becomes less well structured, and rotational and diffusive motions of the hydrating water molecules are increased. This reduction in structure and increase in dynamics are likely the origin of the previously observed increased entropy of hydration as one moves down the halide series. These results also suggest that simple monovalent potassium halide ions induce mostly local perturbations to water structure and dynamics.

Novel accurate modeling of dust loaded wire-duct precipitators using FDM-FMG method on one fine computational domains

Worldwide, electrostatic precipitators (ESP) have been extensively utilized to separate fine particles for diverse large-scale industrial applications. In this regard, this paper presents a novel approach for modeling the dust-loaded ESP on the fine computational domain where the need for a fast solver arises. Unlike the previously published numerical techniques, the finite difference method (FDM) integrated with a full multi-grid method (FMG), labeled FDM-FMG, is developed to resolve Poisson and continuity equations on one fine computational domain. For clean and dust-loaded ESP, the proposed FMG is checked versus successive over-relaxation (SOR) on fine domains where the proposed one is greatly transcendent in terms of convergence characteristics and hence the computational performance (CPU time). For the first time, two major issues are highlighted and solved: the first concerning issue is the chosen ion mobility as an important factor in the simulation results and the second one is choosing an optimal computational grid for dust loaded precipitators that grantees both low truncation and roundoff errors, results in well-matched with experimental measurements nominated in the previous publishing. The novel idea of working on various grid sizes and tracking the optimal ones gives the FDM-FMG an advantage of predicting a precise picture for the electrical situations in industrial ESP over the other numerical techniques. After all, the impact of changing the spacing between the different wires and the height of the ionized wires on the distributions of current, ion, and particle charge densities on the ground are deeply simulated and presented in dust-loaded ESP. The proposed FDM-FMG can be a promising tool for the designers and manufacturers of precipitators, thanks to its superior computational performance.

The aggregation and charging of natural clay allophane: Critical coagulation ionic strength in the presence of multivalent counter-ions

Allophane is an amorphous aluminosilicate clay mineral which is typically found in young volcanic ash soils. The aggregation-dispersion and charging behaviors of allophane may affect the usability and protection of the volcanic ash soils and surrounding environment. To understand the aggregation-dispersion and charging of natural allophane, dynamic and electrophoretic light scattering experiments were carried out at pH 5 as a function of potassium salt concentration and counter-ion (Cl - , SO 4 2- , Fe(CN) 6 3- , and Fe(CN) 6 4- ) valence. The temporal increase of particle hydrodynamic diameters and electrophoretic mobilities (EPM) were measured, and the stability ratio, critical coagulation concentration (CCC), critical coagulation ionic strength (CCIS), zeta potential, and surface charge density were further obtained. The experimental results of stability ratio and EPM of allophane particles were affected by the counter-ion valence, and the CCCs strongly depended on the counter-ion valence. The behavior was well described by the well-known empirical Schulze-Hardy rule. The allophane particles showed a low surface charge density in the presence of multivalent counter-ions. Thus, Derjaguin-Landau and Verwey-Overbeek (DLVO) theory with the Debye-Huckel (DH) approximation was applied to consider the CCIS. The experimental relationship between CCIS and surface charge density was well explained by DLVO theory by taking account of particle size. We conclude that, in the presence of multivalent counter-ions, the DLVO theory with DH approximation has a good applicability to the aggregation-dispersion of natural clay allophane particles. • Counter-ion valence affects the aggregation and charging of allophane particles. • Tetravalent counter-ion induces charge reversal and re-stabilization of allophane. • Critical coagulation ionic strength vs. surface chare follows DLVO theory. • DLVO theory has a good applicability to the aggregation and dispersion of allophane.

Theory of Ionic Liquids with Polarizable Ions on a Charged Electrode

We formulate a general mean-field theory of a flat electric double layer in ionic liquids and electrolyte solutions with ions possessing static polarizability and a permanent dipole moment on a charged electrode. We establish a new analytical expression for electric double layer differential capacitance determining it as an absolute value of the ratio of the local ionic charge density to the local electric field on an electrode surface. We demonstrate that this expression generalizes the analytical expressions previously reported by Kornyshev and Maggs and Podgornik. Using the obtained analytical expression, we explore new features of the differential capacitance behavior with an increase in the static polarizability and permanent dipole moment of cations. We relate these features to the behavior of ionic concentrations on the electrode. In particular, we elucidate the role of the competition between the dielectrophoretic attraction and Coulomb repulsion forces acting on polarizable or polar cations in the electric double layer in the behavior of the differential capacitance. The developed theoretical model and obtained theoretical findings could be relevant for different electrochemical applications, e.g. batteries, supercapacitors, catalysis, electrodeposition, etc.

Interior Electroneutrality in Nernst–Planck–Navier–Stokes Systems

We consider the limit of vanishing Debye length for ionic diffusion in fluids, described by the Nernst-Planck-Navier-Stokes system. In the asymptotically stable cases of blocking (vanishing normal flux) and uniform selective (special Dirichlet) boundary conditions for the ionic concentrations, we prove that the ionic charge density $\rho$ converges in time to zero in the interior of the domain, in the limit of vanishing Debye length ($\epsilon\to 0$). For the unstable regime of Dirichlet boundary conditions for the ionic concentrations, we prove bounds that are uniform in time and $\epsilon$. We also consider electroneutral boundary conditions, for which we prove that electroneutrality $\rho\to 0$ is achieved at any fixed $\epsilon> 0$, exponentially fast in time in $L^p$, for all $1\le p<\infty$. The results hold for two oppositely charged ionic species with arbitrary ionic diffusivities, in bounded domains with smooth boundaries.

Effect of counter ion valence and pH on the aggregation and charging of oxidized carbon nanohorn (CNHox) in aqueous solution

Oxidized carbon nanohorn (CNHox) is one of carbon nanomaterials and has attracted attention due to its unique material properties. To clarify the dispersion, aggregation, and charging behaviors of CNHox in aqueous solutions with different valences of counter ions, K+, Ca2+, La3+, and pH, the stability ratio and electrophoretic mobility of CNHox were investigated by electrophoretic light scattering and time-resolved dynamic light scattering techniques. The CNHox showed pH-dependent negative zeta potential probably due to the de-protonation of carboxylic groups on CNHox. Increasing electrolyte concentration and counter ion valence decreased the magnitude of zeta potential by double layer screening and counter ion adsorption. The stability ratio of CNHox showed clear slow aggregation regime, fast aggregation regime, and critical coagulation concentration (CCC). The CCC decreased with increasing the counter ion valence. That is, the aggregation-dispersion of CNHox follows the Schulze-Hardy rule and the Derjaguin-Landau and Verwey-Overbeek (DLVO) theory. Furthermore, the relationship between critical coagulation ionic strength and charge density reasonably agrees with theoretical prediction by the DLVO theory for low surface potential. The DLVO theory is useful for the description of aggregation-dispersion of irreversible aggregates with colloidal size as found for CNHox aggregate, once their zeta potentials are evaluated.

Comparison of CO2 absorption performance between methyl‐di‐ ethanolamine and tri‐ethanolamine solution systems and its analysis in terms of amine molecules

AbstractThe present study analyzes the features of chemical CO2 absorption using tertiary amine solvents by comparing the absorption performance and electrical properties between methyl‐di‐ethanolamine (MDEA) and tri‐ethanolamine (TEA) systems. The results are mostly attributed to the different structures of the two amine molecules. Absorption performance is significantly affected by the molecular structure and water concentration in the amine solution. The absorption performance of the MDEA system is better than that of TEA, which is basically ascribed to the MDEA molecule's more asymmetric and irregular shape than that of TEA, which thus enhances the catalytic activity of MDEA and the reactivity of the −OH moiety in water. The difference of electrical properties such as ionic conductivities (ICs) of the two protonated amines and real ionic activity coefficients (RIAC) between the two systems might be also caused by the different molecular structures of the two amines. The IC of protonated MDEA is estimated to be 23.70% higher than that of protonated TEA, because of the higher ionic mobility and charge density of MDEA. The RIAC of the MDEA system is higher than that of TEA, which is explained by the different physicochemical interactions between the molecules in the two systems. Since water is one of the reactants in the absorption, its concentration in solution significantly affects the results of the systems. In addition, the absorption using tertiary amine is a base‐catalyzed reaction, and thus variations of the overall absorption rate follow a parabolic curve. Therefore, it is maximized to be 14.2 and 9.8 mmol CO2·L−1·min−1 in the 15 wt% MDEA and TEA solutions, respectively. Finally, the correlated equations for in situ estimation of chemical absorption capacity by electrical conductivity measured during the absorption are derived in the two systems. © 2021 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Charge Effects Provide Ångström-Level Control of Lipid Bilayer Morphology on Titanium Dioxide Surfaces.

Interfaces between molecular organic architectures and oxidic substrates are a central feature of biosensors and applications of biomimetics in science and technology. For phospholipid bilayers, the large range of pH- and ionic strength-dependent surface charge densities adopted by titanium dioxide and other oxidic surfaces leads to a rich landscape of phenomena that provides exquisite control of membrane interactions with such substrates. Using neutron reflectometry measurements, we report sharp, reversible transitions that occur between closely surface-associated and weakly coupled states. We show that these states arise from a complex interplay of the tunable length scale of electrostatic interactions with the length scale arising from other forces that are independent of solution conditions. A generalized free energy potential, with its inputs only derived from established measurements of surface and bilayer properties, quantitatively describes these and previously reported observations concerning the unbinding of bilayers from supporting substrates.

Mobilization of electroosmotic flow markers in capillary zone electrophoresis

UV-absorbing neutral substances are commonly used as markers of mean electroosmotic flow in capillary electrophoresis for their zero electrophoretic mobility in an electric field. However, some of these markers can interact with background electrolyte components and migrate at a different velocity than the electroosmotic flow. Thus, we tested 11 markers primarily varying in their degree of methylation and type of central atom in combination with five background electrolyte cations differing in their ionic radii and surface charge density, measuring the relative electrophoretic mobility using thiourea as a reference marker. Our results from this set of experiments showed some general trends in the mobilization of the markers based on the effects of marker structure and type of background electrolyte cation on the relative electrophoretic mobility. As an example, the effects of an inadequate choice of marker on analyte identification were illustrated in the electrophoretic separation of glucosinolates. Therefore, our findings may help electrophoretists appropriately select electroosmotic flow markers for various electrophoretic systems.

Complexation of Cyclic Glutarimidedioxime with Cerium: Surrogating for Redox Behavior of Plutonium

The complexation of cerium with glutarimidedioxime (H2L) was studied by potentiometry, ESI-mass spectrometry, and cyclic voltammetry. Crystallization of [CeIV(HL)3]+ from Ce3+ starting reactant indicated spontaneous complexation-driven oxidation. In aqueous solution, Ce3+ ions form three successive complexes, Ce(HL)2+, Ce(HL)2+, and Ce(HL)3 (where HL- stands for the singly deprotonated ligand). The interactions of glutarimidedioxime with metal ions are dominantly electrostatic in nature, and the stability constants of the complexes are correlated to the charge density of metal ions. Extrapolations of predicted stability constant (log β) values were made from plotting effective charge and the ionic radius of the metal ion for Pu3+ and Pu4+. The stability constants of PuIV(HL)3+ and PuIII(HL)2+ are estimated to be 27.74 and 19.75, respectively. The differences of stability constants mean that glutarimidedioxime selectively binds Pu4+ over Pu3+ by a factor of about 8 orders of magnitude, suggesting Pu4+ would be stabilized by chelation with glutarimidedioxime. The mechanism of reduction of Pu4+ to Pu3+ in acidic solution is explained by decomposition of glutarimidedioxime through acid hydrolysis rather than a chelation-driven mechanism.

X-ray scattering reveals ion clustering of dilute chromium species in molten chloride medium.

Enhancing the solar energy storage and power delivery afforded by emerging molten salt-based technologies requires a fundamental understanding of the complex interplay between structure and dynamics of the ions in the high-temperature media. Here we report results from a comprehensive study integrating synchrotron X-ray scattering experiments, ab initio molecular dynamics simulations and rate theory concepts to investigate the behavior of dilute Cr3+ metal ions in a molten KCl–MgCl2 salt. Our analysis of experimental results assisted by a hybrid transition state-Marcus theory model reveals unexpected clustering of chromium species leading to the formation of persistent octahedral Cr–Cr dimers in the high-temperature low Cr3+ concentration melt. Furthermore, our integrated approach shows that dynamical processes in the molten salt system are primarily governed by the charge density of the constituent ions, with Cr3+ exhibiting the slowest short-time dynamics. These findings challenge several assumptions regarding specific ionic interactions and transport in molten salts, where aggregation of dilute species is not statistically expected, particularly at high temperature.

Combination of Electrochemical Surface Plasmon Resonance and Molecular Dynamics Simulation to Evaluate the Quasi-Static Capacitance at the Ionic Liquid/Electrode Interface

1. Introduction Composed of ions solely, ionic liquids (ILs) are low-melting point salts exhibiting excellent properties for electrolytes such as ultra-low volatility, non-flammability, thermal/electrochemical stability. The structure and dynamics of the electric double layer (EDL) are critical in the process of charge/mass transfer. However, different from the conventional electrolytes, ILs exhibit strong Coulomb correlation with high concentration and density, hence Gouy-Champman-Stern model is not applicable to describe the EDL of ILs. For the experimental measurement of the differential capacitance in the EDL, electrochemical impedance spectroscopy (EIS) is the most popular method. But the fast ac potential oscillation in EIS measurements can’t avoid the influence of the slow dynamics of the EDL such as ultraslow relaxation[1] and hysteresis.[2] In the present study, electrochemical surface plasmon resonance (ESPR) is proposed as an effective measurement method of static differential capacitance at the IL/electrode interface. The influences of the slow relaxation are demonstrated at different scan rates of potential. In order to achieve quantitative measurement, molecular dynamics (MD) simulations of the IL between two single-layer graphene electrodes are performed. Moreover, through the data analysis of MD, the variations of ionic layer structure and ionic orientation are revealed and described in detail. 2. Methods 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][TFSA−]) was chosen as the IL material for research. In the ESPR experiments, a laser beam was incident through a prism and totally reflected on a 50-nm golden film deposited on a SF15 glass. The golden film was the working electrode, a Pt wire was set as the counter electrode, and an Ag/AgCl wire was inserted into the IL as the quasi-reference electrode. The experiments were performed at different scan rates to determine the influence of slow dynamics.[3] The all-atom MD simulations were performed by using DL_POLY classic. The results in all the charged conditions were simulated from the same initial configuration, which was prepared from IL bulk simulations, vacuum-liquid interface simulations, and uncharged graphene-IL interface simulations.[4] There were 720 ion pairs between two single-layer graphene electrodes within 125 Å. In each charged condition, the charge was allocated evenly to every C atom on the electrodes. The temperature was controlled (NVT ensemble) by using the Berendsen thermostat (0.5 ns as the quick equilibration process) and the Nose-Hoover thermostat (2 ns). Thus, the trajectories in the last 1 ns were chosen as the statistical data for analysis. 3. Results and Discussion By ESPR experiments, the change in SPR angle is recorded simultaneously with cyclic voltammetry, exhibiting a sigmoidal shape with the maximum slope at around −0.6 V (PZC). We find that the variation ranges by the negative scans are larger than those by the positive scans, and the variation range by positive scan increases as the scan rate decreases. These phenomena indicate that the influence of slow dynamics is insignificant for negative scans as was previously observed for a different IL.[1] To study the cause of the sigmoidal change in SPR angle, we propose a mathematical model,[3] by which a linear relationship between SPR angle and the surface charge density at the IL/electrode interface can be established. Consequently, the relative value of the quasi-static differential capacitance is shown in Fig. 1. Comparing with the previous study,[2] we determine the potential of zero charge in this system as −0.61 V, noted as the grey dashed line. This is the first time to obtain the static differential capacitance at the IL/solid electrode, in spite of the relative value. The differential capacitance exhibits a camel-shaped potential dependence, agreeing with the mean-field lattice gas model.[5] For quantitative measurement, MD simulations are performed to produce ionic distributions and surface charge density with respect to potential. By the data fitting of surface charge density and ionic concentration, we estimate the X − 1 as 3.1 mdeg∙cm2∙μC−1. Furthermore, by the observation of the ionic distribution, we confirm the butyl group of C4mim+ in the first ionic layer would provide extra room for the cations in the second layer, resulting in that the state of “ionic crowding” is hardly to occur and the interval of ionic layers varies with the potential on the negatively charged electrode.