Structure Of Electrical Double Layer Research Articles

Double layer capacitors in dye sensitized solar cells with large charge and energy storage capacity and controlled shape of output voltage signals.

The output signals in natural dyes-based solar cells (DSSC) can be either rising or decaying depending on the type of ions present in the system; these ions called added ions, are introduced by the additives: mordant and brighteners. The photon-dye interaction produces electrons, which eventually reach the electrode giving place to a superficially charged electrode in contact with an electrolyte where are the added ions. This combination produces, automatically, an electrical double-layer EDL structure which has important effects on the performance of the system: a) the added ions control, to a large extent, the initial shape of the output signal, giving rise to rising or decaying profiles; b) it is possible to store large amounts of energy and charge at high electric fields. This structure is found in many other systems that have a surface charged in contact with an electrolyte like piezoelectric materials in human body. This assertion was supported by determining important parameters such as the force between charged surfaces on both sides of the interface, the charge density, the energy density, and the capacitance. The Debye length has very small values then, many important quantities depend on this; it is possible to obtain large values for energy UDL ~ 3.6x105 Jm-3 and charge density ρDL ≈ 1.1x107 Cm-3 for double layer capacitors; these values are orders of magnitude larger than the corresponding values for electrostatic capacitors: Uelec ≈ 4.5x10-3 Jm-3 and ρelec ≈ 1.2 Cm-3. A non-linear model was also developed to fit unstable oscillations found in the output profiles produced by abrupt lighting.

Measurement of the double-layer capacitance of Pt(111) in acidic conditions near the potential of zero charge

Quantifying the charge density stored at the Pt(111)/aqueous interface using the double-layer capacitance close to the potential of zero charge (Cdl,PZC) at 0.30 VNHE is of critical importance to elucidating the structure of the electrical double layer (EDL) in the absence of any competing adsorption processes. Marked discrepancies in the values of Cdl for this interface exist in the literature, which we show are likely attributable to the measurement technique used. To directly observe the predicted Gouy-Chapman capacitance minimum at the PZC in the double-layer window between 0.40-0.55 VRHE, anomalously low electrolyte concentrations (0.1 mM HClO4) are needed. The measurement of accurate values of Cdl,PZC is made highly non-trivial by the extremely large solution resistances (∼80-100 kΩ) measured in this required dilute electrolyte as well as the non-negligible deviations from ideal capacitive behaviour (i.e., constant phase element behaviour) displayed even by this well-ordered model electrochemical system. We provide here a comparison between using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and alternating current-cyclic voltammetry (AC-CV) in determining Cdl,PZC for the Pt(111)/HClO4 interface, for different concentrations of the electrolyte. In particular, even when using optimized experimental parameters, we show that the estimated values of Cdl,PZC at 0.1 mM HClO4 still display a marked discrepancy depending on the technique used, ranging from 27-41 μF cm−2. At higher HClO4 concentrations, the discrepancies are much less pronounced. Importantly, however, the measured deviation from Gouy-Chapman theory, as quantified by the Parsons-Zobel plot slope, remains consistent across these techniques, implying that the EDL structure of the Pt(111)/aqueous interface continues to prove anomalous and enigmatic.

A First-Principles Study of the Formation and Regulation of the Electric Double Layers at Cu (0 0 1)/Mineral Oil Interfaces

Abstract Copper-mineral oil interfaces are key components of oil-impregnated power transformers and are commonly believed to be one of their weak points. The formation of an electric double layer (EDL) at this interface as a result of charge accumulation and transfer is crucial to its insulating properties, but a molecular-level understanding of this phenomenon remains unclear. To understand this fundamental aspect, we have investigated the effect of different EDLs on the electric potential and interfacial potential barrier between copper and mineral oil by using first principle calculations. Based on the calculations, the EDL is shown to reduce the interfacial potential barrier and enhance the diffusion of oil molecules at the interface when the copper side is negatively charged and the mineral oil side is positively charged. In contrast, when the copper side is positively charged and the mineral oil side is negatively charged, the corresponding EDL can increase the interfacial potential barrier and reduce the diffusion of oil molecules at this interface. Our findings shed light on the relationship between the structure of EDLs and their electrical properties in oil-impregnated power transformers.

Electric Double Layer Regulator Design through a Functional Group Assembly Strategy towards Long‐lasting Zinc Metal Batteries

Regulating the electric double layer (EDL) structure of the zinc metal anode by using electrolyte additives is an efficient way to suppress interface side reactions and facilitate uniform zinc deposition. Nevertheless, there are no reports investigating the proactive design of EDL‐regulating additives before the start of experiments. Herein, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long‐lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N‐dimethyl‐1H‐imidazole‐1‐sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn2+ ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H2O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H2O‐induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn2+, promotes the de‐solvation of Zn2+ ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NaV3O8·1.5H2O full cell. This study offers an innovative approach to the design of EDL regulators for high‐performance zinc metal batteries.

Electric Double Layer Regulator Design through a Functional Group Assembly Strategy towards Long-lasting Zinc Metal Batteries.

Regulating the electric double layer (EDL) structure of the zinc metal anode by using electrolyte additives is an efficient way to suppress interface side reactions and facilitate uniform zinc deposition. Nevertheless, there are no reports investigating the proactive design of EDL-regulating additives before the start of experiments. Herein, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long-lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N-dimethyl-1H-imidazole-1-sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn2+ ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H2O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H2O-induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn2+, promotes the de-solvation of Zn2+ ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NaV3O8·1.5H2O full cell. This study offers an innovative approach to the design of EDL regulators for high-performance zinc metal batteries.

Reconstruction of Electric Double Layer on the Anode Interface by Localized Electronic Structure Engineering for Aqueous Zn Ion Batteries

AbstractThe electric double layer (EDL) at the electrode/electrolyte interface plays a crucial role to the electrochemical reactions of zinc ion batteries. For Zn anode, the EDL consists of H2O dipoles, which can cause Zn corrosion and passivation. Herein, the localized electronic‐rich (LER) structure performing as soild electrolyte interphase (SEI) changes the electron distribution, leading to the rapid capture of Zn2+, thus promoting the desolvation of the cH2O shell. Moreover, the LER generates an electrostatic repulsion effect to SO42−. Consequently, a unique H2O‐poor EDL is reconstructed with the distribution of Zn2+‐H2O‐SO42−, which inhibits side reactions and improves the deposition kinetics of Zn2+. In situ Raman intuitively confirms that the zinc‐ion‐flux is uniform during the whole electroplating process. LER as regulator for EDL structure, leads to smooth and fast Zn2+ deposition. The performance enhancement is demonstrated by LER@Zn//LER@Zn cells, which exhibit exceptional lifespan for 4800 h. Furthermore, the LER@Zn///MnO2 cell shows improved cycling stability over 1500 cycles, with a high capacity of 124 mAh g−1 at 5 C.

Positively Charged Amino Acid-Modulated Interfacial Chemistry and Deposition Textures for Highly Reversible Zinc Anodes.

Interfacial active water molecule-induced parasitic reactions and stochastic Zn2+ transport-caused dendrite issue significantly impede the implementation of aqueous Zn-ion batteries. Herein, three positively charged amino acids, namely arginine, histidine, and lysine, were utilized as adsorption-type electrolyte additives to enhance the stability and reversibility of Zn anodes. Combined theoretical and experimental analyses verified that these amino acid cations can synergistically modulate the interfacial microenvironment and promote orientational Zn deposition. The adsorbed amino acid cations reconfigured the interfacial electric double layer structure, forming SO42-- and H2O-poor interfaces, thereby retarding hydrogen evolution and corrosion side reactions. Simultaneously, the preferential adsorption of the amino acid cations at specific facets induced crystallographic orientational Zn deposition along unterminated facets. Three deposition architectures, namely planar texture, subvertical alignment, and vertical erection, were obtained, all effectively inhibiting dendrite formation. Consequently, symmetric cells with the three amino acid cations exhibited high stripping/plating reversibility of over 2000 cycles at 5 mA cm-2. Moreover, MnO2-based full cells exhibited markedly improved stabilities compared with their additive-free counterparts.

Demulsification of W/O emulsions induced by terahertz pulse electric fields-driven hydrogen bond disruption of water molecules

Demulsifying highly stable W/O emulsions, composed of heavy oil and water, is crucial for simplifying crude oil processing, reducing production costs, and mitigating environmental pollution. In these emulsions, aromatic components in the oil phase stack via π-π interactions, while hydrogen bonds stabilize the water phase. This leads to the creation of a strong oil-water interface through electrostatic attraction, ultimately hindering water droplet coalescence and oil-water separation. In this study, a 1.0 THz pulse electric field is introduced to effectively disrupt the hydrogen bond network among water molecules by inducing hydrogen bond resonance. This disruption contributes to increased water mobility in the oil phase, weakened stability of the oil-water interface film, and facilitates efficient water droplet coalescence in the oil phase. The results show that throughout the demulsification process, the average number of hydrogen bonds per water molecule rapidly decreases from 1.41 to 1.08 within 100 ps. The upper and lower limits of hydrogen bond lifetimes decrease by 8.12 ps and 3.24 ps, respectively. This indicates a significant disruption in the stability of hydrogen bonds between water molecules. Concurrently, the terahertz pulse electric field disrupts the initially stable oil-water interface film of the emulsion system, leading to a noteworthy reduction in the oil-water interface tension from 54.3 to 39.2 mN·m−1. The self-diffusion coefficient of water molecules increases from 1.33 to 2.62 Å2·ps−1, signifying that water molecules are more inclined to penetrate the interfacial region between the two phases. Additionally, the terahertz pulse electric field induces alterations in the arrangement of water molecules, resulting in the rearrangement of electrons in the water phase and disrupting the originally stable electrical double layer structure of the oil-water interface. This study provides novel insights into the development of efficient and environmentally friendly electric demulsification technologies, holding significant potential for widespread industrial applications.

Uncovering the cation effects on the electroreduction of CO2 on Pd/C catalysts − an SEIRAS study

Electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) has long been known to be affected by the electrolyte cations, yet the interpretations of these effects remain controversial. In this work, taking advantage of the unique catalytic characteristics of Pd, we investigated the cation effects on the CO2RR. It was found that the productions of formate and carbon monoxide (CO) are accelerated, and the competitive hydrogen evolution reaction (HER) is suppressed on Pd surfaces by larger cations. Detailed ATR-SEIRAS measurements revealed the promotion of CO2RR comes from two aspects. First, the CO2 molecules can be concentrated at the electrode–electrolyte interface by larger cations through electrostatic interaction. Second, a stronger interfacial electric field brought by the larger cations can accelerate the CO2RR and stabilize the negatively charged intermediates. The potential-dependent spectral transitions of adsorbed CO and interfacial water shed new light on the cation-dependent electric double layer structures. In light of these findings, the cation effects on the formate and CO pathways at different overpotentials were further revealed.

Steering Selectivity in Electrocatalytic Furfural Reduction via Electrode-Electrolyte Interface Modification.

Electrocatalytic reduction of biomass-derived furfural (FF) represents a sustainable route to produce furfuryl alcohol (FA) and 2-methylfuran (MF) as a value-added chemical and a biofuel, respectively. However, achieving high selectivity for MF as well as tuning the selectivity between FA and MF within one reaction system remain challenging. Herein, we have reported an electrode-electrolyte interface modification strategy, enabling FA and MF selectivity steering under the same reaction conditions. Specifically, by modifying copper (Cu) electrocatalysts with butyl trimethylammonium bromide (BTAB), we achieved a dramatic shift in selectivity from producing FA (selectivity: 83.8%; Faradaic efficiency, FE: 68.9%) to MF (selectivity: 80.1%; FE: 74.8%). We demonstrated that BTAB adsorption over Cu modulates the electrical double layer (EDL) structure, which repels interfacial water and weakens the hydrogen-bond (H-bond) network for proton transfer, thus impeding FF-to-FA conversion by suppression of the hydrogen atom transfer (HAT) process. On the contrary, FF-to-MF conversion was less affected. This work shows the potential of engineering of the electrode-electrolyte interface for selectivity control in electrocatalysis.

Tailoring the Chemical/Electrochemical Response in a Quasi−Solid Polymer Electrolyte Enables the Simultaneous In Situ Construction of Superior Cathodic and Anodic Interfaces

AbstractAlthough the flexibility of the quasi−solid polymer electrolyte favors its surface conformal to the electrode, interfacial damage originating from side reactions between the electrolyte and the electrode remains dominant for battery failure. The design of quasi−solid electrolytes compatible with both aggressive nickel−rich cathode and lithium metal anode persists critical to the application of quasi−solid high−voltage lithium metal batteries (LMBs). Herein, a chemical/electrochemical response strategy is proposed to construct simultaneously stable cathodic and anodic interfaces relying on the synergistic effect of 1,4,7,10,13,16−hexaoxacyclooctadecane (18C6) and LiNO3. The distinctive [18C6Li]+NO3− cluster modifies electric double layer structure by specific adsorption on the electrode, thereby regulating the interfacial layer composition and construction. The NO3− on electrode preferentially decomposes to improve the interfacial performances, leaving the [18C6Li]+ to cut off the side reaction. Furthermore, the 18C6 coordinates with detrimental transition metal ions from NMC811 cathode and converts into useful clusters alleviating the knock−on effect. Thus, the quasi−solid electrolyte with 18C6 and LiNO3 enables Li||NMC811 coin cell to cycle stably over wide operation temperature (0−55 °C), especially, achieving high capacity retention of 79.2% after 300 cycles at 30 °C. This chemical/electrochemical response strategy projects new insights into the design of smart reactive electrolytes for high−voltage LMBs.

Modeling the Electric Double Layer at the Liposome Vesicle via Classical Density Functional Theory: Solution of Poisson's Equations for Curved Membranes.

The electric double layer at the liposome vesicle membrane has been investigated by a modified fundamental-measure theory in the framework of the restricted primitive model. An analytical equation has been obtained for the mean electrostatic potential (MEP) by solving Poisson's equation for curved membranes. This study investigates the influence of vesicle size, membrane thickness, surface charges, and electrolyte concentration on the structure, composition, and width of electric double layers (EDLs) on the inner and outer membrane walls. Our findings indicate that a thin and denser layer of ions is formed at the concave wall of the membrane (inner wall) compared to that at the outer membrane. As expected, the width of the diffuse layer decreases with the concentration and surface charge. Also, when the surface charges on both concave and convex walls are the same, the absolute value of MEPs on the inner membrane, concave wall, is greater than that on the convex wall. We have also investigated the diffuse potential, which decreases with concentration, membrane thickness, and cavity size, whereas it increases with surface charges. As we expect, the contact density of counterions at the inner concave wall of the vesicle cavity is always greater than the corresponding value at the convex wall, whereas this trend reverses for co-ions. Also, the contact density of counterions (co-ions) at the inner wall decreases (increases) with cavity size, whereas it increases at the outer wall (decreases). Finally, depletion of co-ions occurs at the membrane walls with enhancement in surface charges.

Utilizing the Adsorbability of Pseudoboehmite for Tailoring the Stability of an Aluminum Sulfate Alkali-free Accelerator for Shotcrete.

Shotcrete is widely used in tunnels, bridges, culverts, and other large-scale projects. The accelerator is an additive employed to expedite the setting time of shotcrete. Previous research primarily concentrated on enhancing the early strength of accelerators, whereas their long-term stability has been inadequately investigated. In this study, pseudoboehmite (PB) and amorphous aluminum hydroxide (AAH) were incorporated into the accelerator to enhance its stability over a period of 90 days without any signs of crystallization or delamination. Furthermore, the accelerator exhibited an initial setting time of 170 s, a final setting time of 550 s, and a compressive strength of 11.58 MPa after 1 day. The mechanism of effects was studied by isothermal calorimetry, FTIR, XRD, TG-DTG, and SEM analysis. The enhancement in stability is attributed to the distinctive adsorption and thixotropic properties of PB, which facilitate the formation of an electrical double-layer structure in acidic solutions. The expedited setting and hardening are primarily due to the equilibrium between Al3+, SO42-, and Ca2+ ions, which accelerates the hydration process of cement. This research offers a methodology for developing a high-performance, alkali-free liquid accelerator.

Influence of electric double layer rigidity on CO adsorption and electroreduction rate

Understanding the structure of the electric double layer (EDL) is critical for designing efficient electrocatalytic processes. However, the interplay between reactant adsorbates and the concentrated ionic species within the EDL remains an aspect that has yet to be fully explored. In the present study, we employ electrochemical CO reduction on Cu as a model reaction to reveal the significant impact of EDL structure on CO adsorption. By altering the sequence of applying negative potential and elevating CO pressure, we discern two distinct EDL structures with varying cation density and CO coverage. Our findings demonstrate that the EDL comprising densely packed cations substantially hinders CO adsorption on the Cu as opposed to the EDL containing less compact cations. These two different EDL structures remained stable over the course of our experiments, despite their identical initial and final conditions, suggesting an insurmountable kinetic barrier present in between. Moreover, we show that the size and identity of cations play decisive roles in determining the properties of the EDL in CO electroreduction on Cu. This study presents a refined adaptation of the classical Gouy-Chapman-Stern model and highlights its catalytic importance, which bridges the mechanistic gap between the EDL structure and cathodic reactions.

Feroxyhyte - from synthesis and characterization to application.

Feroxyhyte (δ-FeOOH) was synthesized and characterized using X-ray diffractometry (XRD), simultaneous thermal analysis (STA), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and low-temperature nitrogen adsorption-desorption measurements. Its potential application as adsorbent of an anionic and cationic dyes such as C.I. Acid Violet 1 (AV1) and C.I. Basic Blue 3 (BB3) was investigated by determining the adsorption capacities based on the Langmuir (36.6 mg/g for AV1 and 187 mg/g for BB3), Freundlich and Dubinin-Radushkevich isotherm models. Adsorption of AV1 and BB3 by δ-FeOOH drops with the presence of additives such as cationic and anionic surfactants (CTAB, SDS) and ionic polymers (PAA, PEI). The surface and electrokinetic properties of examined suspensions were also described. They include determination of the solid surface charge density and the zeta potential, as well as values of point of zero charge and isoelectric point of feroxyhyte particles without and with adsorbed layers of organic substances. Their analysis made possible to propose the most probable structure of electrical double layer formed at the iron mineral/aqueous solution interface.

Probing the electric double layer structure at nitrogen-doped graphite electrodes by constant-potential molecular dynamics simulations

Electric double layer (EDL) is a critical topic in electrochemistry and largely determines the working performance of lithium batteries. However, atomic insights into the EDL structures on heteroatom-modified graphite anodes and EDL evolution with electrode potential are very lacking. Herein, a constant-potential molecular dynamics (CPMD) method is proposed to probe the EDL structure under working conditions, taking N-doped graphite electrodes and carbonate electrolytes as an example. An interface model was developed, incorporating the electrode potential and atom electronegativities. As a result, an insightful atomic scenario for the EDL structure under varied electrode potentials has been established, which unveils the important role of doping sites in regulating both the EDL structures and the following electrochemical reactions at the atomic level. Specifically, the negatively charged N atoms repel the anions and adsorb Li+ at high and low potentials, respectively. Such preferential adsorption suggests that N-doped graphite can promote Li+ desolvation and regulate the location of Li+ deposition. This CPMD method not only unveils the mysterious function of N-doping from the viewpoint of EDL at the atomic level but also applies to probe the interfacial structure on other complicated electrodes.

Enhancing Zn‐Metal Anode Stability: Key Effects of Electrolyte Additives on Ion‐Shield‐Like Electrical Double Layer and Stable Solid Electrolyte Interphase

AbstractOwing to zinc dendrites and parasitic reactions, aqueous Zn‐metal batteries often suffer from poor reversibility and cyclability. Electrolyte additives present a promising strategy to improve Zn anode stability. However, the ever‐evolving perspectives and mechanisms, paradoxically, complicate battery design, causing a scenario where any electrolyte additive seems to be effective. Herein, it is taken ionic liquid (IL) additives as an example and detailed explored the impact of three typical IL anions, namely OTF−, TFA−, and BF4−. It is identified that the primary determinant of electrolyte additives as their electrical double layer (EDL) structures and their subsequent solid‐electrolyte interface (SEI) composition. An advantageous EDL structure, akin to an ion‐shield, can reduce the absorption of H2O molecules, which further enrich the SEI with zincophilic and hydrophobic components, thereby mitigating parasitic reactions and Zn dendrite formation. As a result, the Zn||Zn cell with optimal [EMIM]OTF additives demonstrates an exceptional cycling life under challenging conditions, its cumulative plated capacity surpasses most previously reported results by utilizing different IL additives. This work extends beyond performance enhancements, representing a valuable exploration of key criteria for electrolyte additives is believed. These insights are expected to offer fundamental guidance for future research and electrolyte design.

Effect of Interlayer Spaces and Interfacial Structures on High-Performance MXene/Ionic Liquid Supercapacitors: A Molecular Dynamics Simulation.

The combination of high-capacitance MXenes and wide-electrochemical-window ionic liquids (ILs) has exhibited bright prospects in supercapacitors. Several strategies, such as surficial functionalization and interlayer spacing tuning, have been used to enhance the electrochemical performance of supercapacitors. However, the lack of theoretical guidance on these strategies, including the effects of the microenvironment in the interlayer of confined ILs, hindered the further exploration of such devices. Herein, we performed molecular dynamics simulations to comprehensively investigate the effects of the interlayer space and surface terminations of MXene electrodes on capacity. The results show that the electrical double layer (EDL) structure was found to form on the interface between the MXene electrode and ILs electrolyte by analyzing the ion number density and charge density in the nanometer confined spaces. Under the same potential, the -OH terminations significantly impact the ion orientation in the EDL, particularly near the electrode surface, where cations tend to align vertically, allowing the retention of more cations at the electrode surfaces. Interestingly, such an orientation distribution was decisively from the hydrogen bonds expressed by O-H···O between the -OH termination of MXene and -OH groups of ILs. The differential capacitances of the supercapacitors were calculated by the surficial electron density, and it showed that the capacitance is a nearly one-quarter increase in the 14 Å interlayer spacing compared with that of 10 Å under an applied potential of 2 V. At the same time, the Ti3C2(OH)2 electrode had a higher differential capacitance than the Ti3C2O2 electrode, which possibly originates from the stronger hydrogen bonds to contribute to the vertical aggregation of the cations. Our results highlighted the roles of the interlayer spacing distance and surface terminations of the MXene on the performance of the type of supercapacitor.

Water dynamics and sum-frequency generation spectra at electrode/aqueous electrolyte interfaces.

The dynamics of water at interfaces between an electrode and an electrolyte is essential for the transport of redox species and for the kinetics of charge transfer reactions next to the electrode. However, while the effects of electrode potential and ion concentration on the electric double layer structure have been extensively studied, a comparable understanding of dynamical aspects is missing. Interfacial water dynamics presents challenges since it is expected to result from the complex combination of water-water, water-electrode and water-ion interactions. Here we perform molecular dynamics simulations of aqueous NaCl solutions at the interface with graphene electrodes, and examine the impact of both ion concentration and electrode potential on interfacial water reorientational dynamics. We show that for all salt concentrations water dynamics exhibits strongly asymmetric behavior: it slows down at increasingly positively charged electrodes but it accelerates at increasingly negatively charged electrodes. At negative potentials water dynamics is determined mostly by the electrode potential value, but in contrast at positive potentials it is governed both by ion-water and electrode-water interactions. We show how these strikingly different behaviors are determined by the interfacial hydrogen-bond network structure and by the ions' surface affinity. Finally, we indicate how the structural rearrangements impacting water dynamics can be probed via vibrational sum-frequency generation spectroscopy.

Properties of aqueous electrolyte solutions at carbon electrodes: effects of concentration and surface charge on solution structure, ion clustering and thermodynamics in the electric double layer.

Surfaces are able to control physical-chemical processes in multi-component solution systems and, as such, find application in a wide range of technological devices. Understanding the structure, dynamics and thermodynamics of non-ideal solutions at surfaces, however, is particularly challenging. Here, we use Constant Chemical Potential Molecular Dynamics (CμMD) simulations to gain insight into aqueous NaCl solutions in contact with graphite surfaces at high concentrations and under the effect of applied surface charges: conditions where mean-field theories describing interfaces cannot (typically) be reliably applied. We discover an asymmetric effect of surface charge on the electric double layer structure and resulting thermodynamic properties, which can be explained by considering the affinity of the surface for cations and anions and the cooperative adsorption of ions that occurs at higher concentrations. We characterise how the sign of the surface charge affects ion densities and water structure in the double layer and how the capacitance of the interface-a function of the electric potential drop across the double layer-is largely insensitive to the bulk solution concentration. Notably, we find that negatively charged graphite surfaces induce an increase in the size and concentration of extended liquid-like ion clusters confined to the double layer. Finally, we discuss how concentration and surface charge affect the activity coefficients of ions and water at the interface, demonstrating how electric fields in this region should be explicitly considered when characterising the thermodynamics of both solute and solvent at the solid/liquid interface.