Search

[Display omitted] The behavior of cucurbit[6]uril at the electrode/solution interface in the presence of magnesium sulfate was investigated and quantified. It has been established that at the highest positive potential available for the adsorption of organic compounds, a structure is formed that consists entirely of neutral cavitand molecules. [ABSTRACT FROM AUTHOR]

MoS2 nanomaterials and ionic liquids (ILs) have attracted tremendous interest as the prime electrodes and electrolytes of supercapacitors. However, the corresponding charge storage mechanisms have not yet been clearly understood. Herein, we study the molecular-level energy storage mechanisms of the MoS2 electrode in imidazolium ionic liquid ([BMI+][PF6−]) using molecular dynamics (MD) simulation. The electric double-layer (EDL) structures of MoS2 electrodes in [BMI+][PF6−] electrolytes are comprehensively studied in terms of number density, MD snapshots, separation coefficient, and ion-electrode interaction energy. Based on this, the electric potential and electric field distributions are calculated by integrating Poisson equations. Importantly, a bell-shaped differential capacitance profile is proposed, different from the U-shaped curve from the conventional Gouy–Chapman theory. Especially, it can be well reproduced by the differential charge density curve in the Helmholtz layer. This indicates that the capacitive behaviors of the MoS2 electrode are primarily determined by the counterion population/structure in the EDL region 5.0 Å from the electrode surface. In the end, ion diffusion coefficients within different interfacial EDL regions are evaluated, revealing that dynamics are significantly suppressed by ~50% in the Helmholtz region. However, the dynamics can be recovered to a bulk state with the ion position 10 Å away from the electrode surface. The as-obtained insights reveal the charge storage mechanisms of MoS2 in ILs, which can provide useful guidance on improving the energy density of MoS2 supercapacitors. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to investigate the possibility of using the dipole dimer as water model in describing the electrical double layer capacitor capacitance behaviors. Several points are confirmed. First, the use of the dipole dimer water model enables several experimental phenomena of aqueous electrical double layer capacitance to be achievable: suppress the differential capacitance values gravely overestimated by the hard sphere water model and continuum medium water model, respectively; reproduce the negative correlation effect between the differential capacitance and temperature, insensitivity of the differential capacitance to bulk electrolyte concentration, and camel–shaped capacitance–voltage curves; and more quantitatively describe the camel peak position of the capacitance–voltage curve and its dependence on the counter-ion size. Second, we fully illustrate that the electric dipole plays an irreplaceable role in reproducing the above experimentally confirmed capacitance behaviors and the previous hard sphere water model without considering the electric dipole is simply not competent. The novelty of the paper is that it shows the potential of the dipole dimer water model in helping reproduce experimentally verified aqueous electric double layer capacitance behaviors. One can expect to realize this potential by properly selecting parameters such as the dimer site size, neutral interaction, residual dielectric constant, etc. [ABSTRACT FROM AUTHOR]

In this paper, we developed a multi-physics model of an electrostatic MEMS resonator made of an array of mechanically-coupled beams and investigate its potential use for mass detection applications. Experiments were conducted on two- and three-coupled beams under electrostatic actuation to verify the capability of the model to predict the mechanical response of coupled beam arrays. The fabricated device, comprising polysilicon-coupled microbeams, is produced using the Multi-User MEMS Processes, followed by an experimental investigation. Numerical results were found in good agreement with their experimental counterparts. The developed model was used to demonstrate the possible adjustment of the electrostatic actuation to enhance the sensitivity of the dynamic response of the coupled MEMS resonator to mass perturbations. By leveraging the mode localization phenomenon and incorporating a novel differential capacitance sensing mechanism, a notable 84% improvement in sensitivity when switching from two-beam to three-beam system while operating near the second mode in the linear regime. Actuating the MEMS device at higher voltages enabled to achieve higher sensitivity thanks to the activation of nonlinear effects such as bifurcation and softening. We observed the transition from nonlinear to nearly-linear dynamic response of the coupled beams upon the addition of mass and demonstrated how bifurcations that cause a sudden shift to a high-amplitude motion can be utilized in differential capacitance-based mass sensing. Additionally, the suggested detection mechanism allows for overcoming the inherent parasitic capacitance, thereby mitigating low signal-to-noise ratios. [Display omitted] [ABSTRACT FROM AUTHOR]

Environmental degradation and climate change caused by excessive CO2 emissions have become the most serious challenges facing humanity. The electrocatalytic CO2 reduction reaction (CO2RR) is an ideal way to produce high‐value chemicals and solve environmental pollution at the same time. The electric double layer (EDL) structure at the electrochemical interface can greatly influence the local catalytic environment, but it is not fully understood. Herein, recent advances in EDL structure for CO2RR are focused. The main components of the EDL, including adsorbates on the electrode surface, metal/water interface, cations, anions, and differential capacitance are described. The latest experimental and theoretical understanding of EDL and their impact on CO2RR are presented. Finally, the current challenges encountered and the outlook for future development are discussed. This review describes the influence of EDL structure on CO2 reduction, which is of guiding significance for the design of new and efficient CO2 electrocatalysts.

We investigate the rich potential of the multi-modal motions of electrostatically actuated asymmetric arch microbeams to design higher sensitivity and signal-to-noise ratio (SNR) inertial gas sensors. The sensors are made of fixed–fixed microbeams with an actuation electrode extending over one-half of the beam span in order to maximize the actuation of asymmetry. A nonlinear dynamic reduced-order model of the sensor is first developed and validated. It is then deployed to investigate the design of sensors that exploit the spatially complex and dynamically rich motions that arise due to veering and modal hybridization between the first symmetric and the first anti-symmetric modes of the beam. Specifically, we compare among the performance of four sensors implemented on a common platform using four detection mechanisms: classical frequency shift, conventional bifurcation, modal ratio, and differential capacitance. We find that frequency shift and conventional bifurcation sensors have comparable sensitivities. On the other hand, modal interactions within the veering range and modal hybridization beyond it offer opportunities for enhancing the sensitivity and SNR of bifurcation-based sensors. One method to achieve that is to use the modal ratio between the capacitances attributed to the symmetric and asymmetric modes as a detector, which increases the detection signal by three orders of magnitude compared to a conventional bifurcation sensor. We also present a novel sensing mechanism that exploits a rigid arm extending transversely from the arch beam mid-point and placed at equal distances between two side electrodes. It uses the asymmetry of the arch beam motions to induce rotary motions and realize a differential sensor. It is found to increase the detection signal by two orders of magnitude compared to a conventional bifurcation sensor. [ABSTRACT FROM AUTHOR]

Electrochemical properties of cationic complexes of supramolecular cavitands from the cucurbit[n]uril (CBns) family are studied. Based on the analysis of a complex of systematic data on these compounds, basic regularities characterizing their adsorption behavior are formulated, in particular, the extremely high surface activity and unusually wide adsorption potential region over which the adsorption layer structure is transformed upon changes of the electrode charge value and sign. The varying of concentrations of reactants involved in the complex-formation reaction (the cavitand and inorganic cation) in the studied systems is shown to change significantly the observed picture of adsorption phenomena. The comparative analysis of adsorption data for systems containing supramolecular complexes of cucurbiturils with different cations can back qualitative estimating of their strength constants. It has been established by example of systems containing inclusive complexes of the СВ7 cavitand with organic cation (the cation of 3,3′-diethylthiocarbocyanine iodide dye) and with organic molecules (super-tough complexes with 1-hydroxyadamantan and ferrocene, the strength constants K of 109–1010 М–1 by order of magnitude), that including of neutral organic molecule into the cavitand cavity does not prevent the formation of an exclusive complex with sodium cation and that such a complex is not formed in the presence of organic cation in the cavitand cavity. It was demonstrated by example of the cobaltocene(Сос)/cobaltocenium(Сос+) redox-system studied in the solutions added with СВ7 and СВ7-free ones that the formation of adsorption layer of the Сос+ ⊂ СВ7 supramolecular complex particles preceding an electrode process leads to changing of the electrode reaction rate and mechanism. [ABSTRACT FROM AUTHOR]

Differential capacitance curves and the zero-charge potentials on liquid renewable (In–Ga)- (14.2 at % In) and Hg-electrodes in solutions with different concentrations of a surface-inactive electrolyte in 1-propanol (1-PrOH) were obtained using an alternating current bridge and the jet electrode method at 32°С. The structure of the electric double layer at the (In–Ga)/1-PrOH and Hg/1-PrOH interfaces is shown to differ, which is due to the influence of the metal nature on both the chemisorption and the metal–1-PrOH physical interaction. The passing from Hg to (In–Ga) is accompanied by a decrease in the distance of the closest approach of the PrOH dipoles to the metal surface and an increase in the metal–1-PrOH chemisorption interaction. The 1-PrOH chemisorption at the (In–Ga) electrode shifts the zero-charge potential toward negative values, which suggests that chemisorbed 1-PrOH dipoles are oriented with their negative (oxygen) ends to the metal surface. Comparison of the experimental results on (In–Ga)- and Hg-electrodes in water, MeOH, EtOH, and 1-PrOH showed that the replacement of one of the hydrogen atoms in the water molecule by an aliphatic radical upon passing to MeOH and the subsequent increase in the radical length upon further passing to EtOH and 1-PrOH affects the shape of the charge dependence of the parameters reflecting the chemisorption specificity of the metal–solvent contact. With increase in the aliphatic radical length, the (In–Ga)–alcohol chemisorption interaction manifests itself at less negative values of the charge density, and the values of the solvent chemisorption potential drop on the (In–Ga)-electrode increased in the series H2O < MeOH < EtOH < (1-PrOH) due to an increase in the donor number of the solvent. The length of the aliphatic radical in the alcohol molecule is shown not to affect the parameters characterizing the physical specifics of the metal–solvent contact, but changes the charge window in which these parameters are recorded. Differential capacitance curves and zero-charge potentials of (In–Ga) electrode in 0.1 M solutions of LiCl, LiBr, and LiI in 1-propanol are obtained. The specific adsorption of halide anions at the (In–Ga)/(1-PrOH) interface is shown to increase in the sequence Cl– < Br– < I–. [ABSTRACT FROM AUTHOR]

This study is on the optimisation of the interface of the p-silicin/indigo camine for electrochemical sensors applications. In this study carried out in cyclic voltammetry, the p-type silicon paste electrode is in contact with the indigo carmine solution at pH = 10. The nature of the current in the silicon / aqueous alkaline solution of indigo carmine junction was determined. The cyclic voltammogram is correlated by an affine straight-line, which allows the determination of the capacitance of the junction at a frequency of 50 Hz.. Curve C-2 = f (E) obtained is not linear. It is of Gaussian form. This form reflects that the ionization of the deep levels of the semiconductor began before the depopulation of the valence band. This study allows to determine the surface potential (Vs = -0,4V) and the flat band potential (VBP = -1,50V). The fermi potential is equal to 1, 50 These results are indications that this interface could not be used as an electrochemical sensor under these conditions. [ABSTRACT FROM AUTHOR]

In this work, we present a mean-field model that takes into account the key components of electrical double layer theory at the interface between an electrode and an electrolyte solution. The model considers short-range specific interactions between different species, including electrode-ion repulsion, the hydration of ions, dielectric saturation of solvent (water), and excluded volume (steric) interactions between species. By solving a modified Poisson-Boltzmann equation, which is derived from the grand thermodynamic potential of an inhomogeneous electrolyte solution, and using the appropriate results of quantum chemistry calculations on the hydration of ions, we can accurately approximate the differential capacitance profiles of aqueous electrolyte solutions at the boundary with a silver electrode. The specific interactions between the ions and the electrodes in the systems under consideration (aqueous solutions of NaClO 4 and KPF 6 ) are assumed to be significantly weaker than their Coulomb interactions. A novel aspect of our research is the investigation of the impact of short-range ion-water interactions on the differential capacitance, which provides new insights into the behavior of the electrical double layer. This model has the potential to be useful for electrochemical engineers working on the development of supercapacitors and related electrochemical energy storage devices. It serves as a basis for future modeling of electrolyte systems on real electrodes, especially in scenarios where chemical ion-electrode interactions are significant., (© 2024 Wiley-VCH GmbH.)

The classical density functional theory (CDFT) is applied to investigate influences of electrode dielectric constant on specific differential capacitance C d and specific energy storage E of a cylindrical electrode pore electrical double layer. Throughout all calculations the electrode dielectric constant varies from 5, corresponding to a dielectric electrode, to ε w r = 108 corresponding to a metal electrode. Main findings are summarized as below. (i): By using a far smaller value of the solution relative dielectric constant ε r = 10 , which matches with the reality of extremely narrow tube, one discloses that a rather high saturation voltage is needed to attain the saturation energy storage in the ultra-small pore. (ii): Use of a realistic low ε r = 10 value brings two obvious effects. First, influence of bulk electrolyte concentration on the C d is rather small except when the electrode potential is around the zero charge potential; influence on the E curve is almost unobservable. Second, there remain the C d and E enhancing effects caused by counter-ion valency rise, but strength of the effects reduces greatly with dropping of the ε r value; in contrast, the C d and E reducing effects coming from the counter-ion size enhancing remain significant enough for the low ε r value. (iii) A large value of electrode relative dielectric constant ε r w always reduces both the capacitance and energy storage; moreover, the effect of the ε r w value gets eventually unobservable for small enough pore when the ε r w value is beyond the scope corresponding to dielectric electrode. It is analyzed that the above effects take their rise in the repulsion and attraction on the counter-ions and co-ions caused by the electrode bound charges and a strengthened inter-counter-ion electrostatic repulsion originated in the low ε r value. [ABSTRACT FROM AUTHOR]

Heterostructure shows superior catalytic performance since it inherits the catalytic properties of the components, and has the advantages of van der Waals interaction. Herein, we build a vacancy-van der Waals heterostructure with MoTe 2 and WTe 2 which forms a capacitor tuning performance, playing an important role in the energy barrier balance of the catalytic reaction. By using the grand canonical reaction kinetics (GCP-K) to explore the electrocatalytic, we predict the Tafel slope of the HER reaction is 81.31 mV/dec through changing applied potential. [Display omitted] • We used van der Waals interaction to design a new vacancy-heterostructure system. • We proposed a capacitor model which participates in the HER reaction. • We used GCP-K to obtain the Tafel slope (81.31 mV/dec) which is closer to experiment than CHE method. [ABSTRACT FROM AUTHOR]

An approximate and analytical solution is obtained for a modified Poisson−Boltzmann (MPB) equation describing +z/−z electrolyte confined inside a cylindrical pore. Three expressions are obtained for the ration of surface charge density, , to surface potential, , electrical potential distribution, and ion concentration profiles. The expression is in near-perfect agreement with the numerical solution for any values of and pore radius non-dimensionalized by screening constant . The expression is applied to study electrical capacitance and energy storage behavior of the cylindrical pore supercapacitor. The MPB calculations accord with previous results from computer simulation and other theories. Main new findings are summarized as follows. (i) Influence of bulk salt mole concentration is mainly manifested in that high value lowers the saturation energy storage density and the threshold electrode potential , beyond which the is just reached, and reduces the width of the zero energy domain around the zero charge potential. The effect of value is only obvious in narrow pore. (ii) Although an increase in size of the ion reduces the value, it simultaneously reduces the value. Moreover, it brings a transition from camel shaped to bell shaped differential capacitance curve. (iii) High ion valency helps in raising both the and values. Moreover, the -enhancing effect by the pore size reduces with the ion valency increasing. (iv) Large size pore raises both the and the values. [ABSTRACT FROM AUTHOR]

This study proposes a split-type pressure sensor based on differential capacitance that can be applied to in-situ accurate pressure testing in high-temperature environments. The sensor is mainly composed of a high-temperature resistant chip and a high-temperature resistant encapsulation structure. The chip is made of a ceramic substrate and presents a differential capacitance structure that can withstand high temperatures and effectively restrain the temperature drift. The encapsulation presents a split-type structure, in which the chip and the test circuit board are placed at the front and back ends of the sensor, respectively. Therefore, the front end of the sensor can work in the high-temperature area for in-situ testing, while the back-end temperature remains below 60°C all the time, which ensures normal operation of the circuit board. Finally, the test results show that the pressure sensor's temperature drift coefficient is only 6.6% within the temperature range of 25°C-400°C. The sensor's sensitivity can reach 9.27 mV/kPa and the maximum repeatability error is less than 2.2% at 400°C, which shows that the proposed sensor has a higher working temperature and higher precision than the existing pressure sensors.

We present a study of the structure and differential capacitance of electric double layers of aqueous electrolytes. We consider electric double layer capacitors (EDLC) composed of spherical cations and anions in a dielectric continuum confined between a planar cathode and anode. The model system includes steric as well as Coulombic ion-ion and ion-electrode interactions. We compare results of computationally expensive, but "exact" , Brownian Dynamics (BD) simulations with approximate, but cheap, calculations based on classical Density Functional Theory (DFT). Excellent overall agreement is found for a large set of system parameters, including variations in concentration, ionic size- and valency-asymmetries, applied voltages and electrode separation, provided the differences between the canonical ensemble of the BD simulations and the grand-canonical ensemble of DFT are properly taken into account. In particular, a careful distinction is made between the differential capacitance C N at fixed number of ions and C μ at fixed ionic chemical potential. Furthermore, we derive and exploit their thermodynamic relations. In the future these relations will also be useful for comparing and contrasting experimental data with theories for supercapactitors and other systems. The quantitative agreement between simulation and theory indicates that the presented DFT is capable of accounting accurately for coupled Coulombic and packing effects. Hence it is a promising candidate to cheaply study room temperature ionic liquids at much lower dielectric constants than that of water. [ABSTRACT FROM AUTHOR]

We investigate the rich potential of the multi-modal motions of electrostatically actuated asymmetric arch microbeams to design higher sensitivity and signal-to-noise ratio (SNR) inertial gas sensors. The sensors are made of fixed–fixed microbeams with an actuation electrode extending over one-half of the beam span in order to maximize the actuation of asymmetry. A nonlinear dynamic reduced-order model of the sensor is first developed and validated. It is then deployed to investigate the design of sensors that exploit the spatially complex and dynamically rich motions that arise due to veering and modal hybridization between the first symmetric and the first anti-symmetric modes of the beam. Specifically, we compare among the performance of four sensors implemented on a common platform using four detection mechanisms: classical frequency shift, conventional bifurcation, modal ratio, and differential capacitance. We find that frequency shift and conventional bifurcation sensors have comparable sensitivities. On the other hand, modal interactions within the veering range and modal hybridization beyond it offer opportunities for enhancing the sensitivity and SNR of bifurcation-based sensors. One method to achieve that is to use the modal ratio between the capacitances attributed to the symmetric and asymmetric modes as a detector, which increases the detection signal by three orders of magnitude compared to a conventional bifurcation sensor. We also present a novel sensing mechanism that exploits a rigid arm extending transversely from the arch beam mid-point and placed at equal distances between two side electrodes. It uses the asymmetry of the arch beam motions to induce rotary motions and realize a differential sensor. It is found to increase the detection signal by two orders of magnitude compared to a conventional bifurcation sensor.

The aim of the present paper is to investigate the possibility of using the dipole dimer as water model in describing the electrical double layer capacitor capacitance behaviors. Several points are confirmed. First, the use of the dipole dimer water model enables several experimental phenomena of aqueous electrical double layer capacitance to be achievable: suppress the differential capacitance values gravely overestimated by the hard sphere water model and continuum medium water model, respectively; reproduce the negative correlation effect between the differential capacitance and temperature, insensitivity of the differential capacitance to bulk electrolyte concentration, and camel–shaped capacitance–voltage curves; and more quantitatively describe the camel peak position of the capacitance–voltage curve and its dependence on the counter-ion size. Second, we fully illustrate that the electric dipole plays an irreplaceable role in reproducing the above experimentally confirmed capacitance behaviors and the previous hard sphere water model without considering the electric dipole is simply not competent. The novelty of the paper is that it shows the potential of the dipole dimer water model in helping reproduce experimentally verified aqueous electric double layer capacitance behaviors. One can expect to realize this potential by properly selecting parameters such as the dimer site size, neutral interaction, residual dielectric constant, etc.

Recently in our work it was shown that the catalytic efficiency of organic compound oxidation in the presence of electrochemically generated radical cations of aromatic di-N-oxides was increased several times using single-walled (SWCNT) or multi-walled (MWCNT) carbon nanotube paper electrodes instead of glassy carbon (GC) electrode. It was found that, in the absence of substrate, the oxidation currents of di-N-oxides at SWCNT or MWCNT paper electrodes, in contrast to the GC electrode, exceeded the oxidation current of the ferrocene (Fc) reference several times. In this work, the study of 2,5-di-Me-pyrazine-di-N-oxide (Pyr1) and Fc oxidation in 0.1 M Bu4NClO4 solutions in acetonitrile (MeCN) at GC, SWCNT and MWCNT paper electrodes was performed by methods of cyclic voltammetry, electron paramagnetic resonance (EPR) electrolysis, and differential capacitance. Quantum chemical modeling of adsorption of Pyr1, Fc, and MeСN on CNT surface was carried out using a cluster model describing the surface of conducting and non-conducting carbon nanotubes. The adsorption energies, equilibrium distances for molecular location and orientation on CNT surface were obtained. The observed effects were explained on the basis of quantum chemical modeling of the non-covalent interaction of the components of the studied system with CNT surface.

The carrier transport in uniaxial strained Si N channel metal oxide semiconductor field effect transistor (NMOSFET) irradiated by gamma rays is analysed. Based on the total dose irradiation effect, an analytical model for differential capacitance of uniaxial strained Si Nano NMOSFET is established. Based on this model, numerical calculation is carried out by MATLAB. The influence of geometric parameters and total dose on differential capacitance is simulated. Meanwhile, the simulation results match the calculation results very well, which validate the accuracy of the model. Therefore, the model provides a good reference for the irradiation reliability of uniaxial strained Si nano NMOSFET and the application of strained integrated circuits. [ABSTRACT FROM AUTHOR]

The mean-field theoretical model of the electric double layer which takes into account the asymmetric finite size of anions and cations and the orientational ordering of water dipoles in the Stern and the diffuse layers is described together with a short description of the main concepts and a brief review of the literature in the theory of the electric double layer. As an example of the application of the described mean-field lattice model of the electric double layer, the influence of different sizes of anions and cations, the influence of the thickness of the Stern layer and the influence of the orientational ordering of water molecules on the asymmetric, bimodal camel-like dependence of differential capacitance on the surface potential is theoretically considered. The presented theoretical model of the electric double layer is flexible enough to be in the future extended to more complicated multicomponent systems with molecules of different sizes and the orientational ordering of molecules.

The classical density functional theory (CDFT) is applied to investigate influences of electrode dielectric constant on specific differential capacitance Cd and specific energy storage E of a cylindrical electrode pore electrical double layer. Throughout all calculations the electrode dielectric constant varies from 5, corresponding to a dielectric electrode, to εwr= 108 corresponding to a metal electrode. Main findings are summarized as below. (i): By using a far smaller value of the solution relative dielectric constant εr=10, which matches with the reality of extremely narrow tube, one discloses that a rather high saturation voltage is needed to attain the saturation energy storage in the ultra-small pore. (ii): Use of a realistic low εr=10 value brings two obvious effects. First, influence of bulk electrolyte concentration on the Cd is rather small except when the electrode potential is around the zero charge potential; influence on the E curve is almost unobservable. Second, there remain the Cd and E enhancing effects caused by counter-ion valency rise, but strength of the effects reduces greatly with dropping of the εr value; in contrast, the Cd and E reducing effects coming from the counter-ion size enhancing remain significant enough for the low εr value. (iii) A large value of electrode relative dielectric constant εrw always reduces both the capacitance and energy storage; moreover, the effect of the εrw value gets eventually unobservable for small enough pore when the εrw value is beyond the scope corresponding to dielectric electrode. It is analyzed that the above effects take their rise in the repulsion and attraction on the counter-ions and co-ions caused by the electrode bound charges and a strengthened inter-counter-ion electrostatic repulsion originated in the low εr value.

The capacitance of Lithium-ion Capacitors (LiCs) highly depends on their terminal voltage. Previous research found that it varies in a nonlinear manner with respect to the voltage. However, none of them modeled the capacitance evolution while considering the physicochemical phenomena that happen in a LiC cell. This paper focuses on developing a new capacitance model that is based on the Stern model of the electrochemical double layer capacitance. The model accounts for the asymmetric V-shape of the C(V) curve, which reflects the variation of the capacitance with respect to the voltage. The novelty of this study concerns the development of a model for LiCs that relies on the fundamental theory of Stern for the differential capacitance. The basic model of Stern is modified in order to account for the hybrid physicochemical structure of LiCs. Moreover, the model was applied to three aged cells to which accelerated calendar aging tests were applied at three voltage values: 2.2, 3 and 3.8 V. A drift of the voltage corresponding to the minimum capacitance was detected for the aged cells. This voltage is related to the neutral state of the positive electrode. The main cause of this phenomenon concerns the loss of lithium ions from the negative electrode of a LiC. In addition, capacitance values decreased after aging, showing an eventual blocking of the pores of the positive electrode. Therefore, the analysis of the C(V) curve was found to be an interesting tool for the interpretation of aging mechanisms. [ABSTRACT FROM AUTHOR]

Ions in the bulk of solvent‐free ionic liquids bind into ion pairs and clusters. The competition between the propensity of ions to stay in a bound state, and the reduction of the energy when unbinding in electric field, determines the portion of free ions in the electrical double layer. We present the simplest possible mean‐field theory to study this effect. "Cracking" of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid. The predictions from the theory are verified and further explored by molecular dynamics simulations. A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape, despite the low concentration of free charge carriers, because the dielectric response reduces the threshold concentration for the bell‐ to camel‐shape transition. The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer. But in spite of the simplicity of the model, its findings demonstrate a clear physical effect: a preference to be a charged monopole rather than a dipole (or higher order multipole) in strong electric field. [ABSTRACT FROM AUTHOR]

The theoretical model, which is based on the density functional approach, has been developed for studying the electrostatic properties of electrolytes with the soft, hydration-mediated ion–ion and ion–surface interactions. The theory approximates the hydration-mediated ion–ion interaction through the mean-field approximation. The results show that the theory leads to a good agreement with the simulation results and predicts the camel-to-bell shape transition for the charged hard-core Yukawa ions with the hydration-mediated interaction. The high C d i f f is observed at a low bulk concentration of ions and the camel-to-bell shape transition occurs when the bulk concentration rises to an appropriate value. The increase of an ion size shifts the maximum differential capacitance ( C d i f f ) to a low surface charge density. The addition of a repulsive hydration interaction reduces the C d i f f , whereas the attractive hydration interaction enhances the C d i f f . The increase of ion–surface and ion–ion interactions decreases the C d i f f and shifts the maximum C d i f f to a higher surface charge density. The increase of hydration anion–anion repulsion decreases the C d i f f of a positively charged electrode and shifts its maximum to more positively charged surfaces. [ABSTRACT FROM AUTHOR]

Recent advances in studies of ionic liquids (IL) and ionic liquid–solvent mixtures are reviewed. Selected experimental, simulation, and theoretical results for electrochemical, thermodynamical, and structural properties of IL and IL-solvent mixtures are described. Special attention is paid to phenomena that are not predicted by the classical theories of the electrical double layer or disagree strongly with these theories. We focus on structural properties, especially on distribution of ions near electrodes, on electrical double layer capacitance, on effects of confinement, including decay length of a dissjoining pressure between confinig plates, and on demixing phase transition. In particular, effects of the demixing phase transition on electrochemical properties of ionic liquid–solvent mixtures for different degrees of confinement are presented.

Molecular dynamics simulations of the electrical double layer at electrode–ionic liquid interfaces allow for molecular level interpretation of the interfacial phenomena and properties, such as differential capacitance (C). In this work, we have simulated an ionic liquid – 1-butyl-3-methylimidazolium hexafluorophosphate – at three gold surfaces, namely: Au(100), Au(110), and Au(111) surfaces. Atomic corrugation of the gold surface leads to higher C values due to the rapprochement of the surface and electrolyte charge planes. Likewise, by accounting for the shift of surface charge plane position towards the electrolyte also results in higher C values. The presented insight shows that a simple correction to the simulation data improves the agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The mean-field theoretical model of the electric double layer which takes into account the asymmetric finite size of anions and cations and the orientational ordering of water dipoles in the Stern and the diffuse layers is described together with a short description of the main concepts and a brief review of the literature in the theory of the electric double layer. As an example of the application of the described mean-field lattice model of the electric double layer, the influence of different sizes of anions and cations, the influence of the thickness of the Stern layer and the influence of the orientational ordering of water molecules on the asymmetric, bimodal camel-like dependence of differential capacitance on the surface potential is theoretically considered. The presented theoretical model of the electric double layer is flexible enough to be in the future extended to more complicated multicomponent systems with molecules of different sizes and the orientational ordering of molecules. [ABSTRACT FROM AUTHOR]

The electric double layer (EDL) structure on a renewable liquid (Cd Ga) (0.3 at.% Cd) electrode in solutions of surface-inactive electrolyte is studied in a solvent with a high donor number, namely, dimethyl sulfoxide (DMSO). The following parameters: the potential of zero charge (PZC) unaffected by specific adsorption of ions, the value of "corrected electrochemical work function", and the potential drop due to chemisorption of solvent are obtained on (Cd Ga)/DMSO interface and are compared with analogous results on Hg/DMSO, (Tl Ga)/DMSO, (In Ga)/DMSO, Ga/DMSO, (Cd Ga)/acetonitrile (AN), (Cd Ga)/gamma-butyrolactone (GBL), and (Cd Ga)/dimethylformamide (DMF) interfaces. The chemisorption of DMSO molecules in the Helmholtz layer shifts the potential of the (Cd Ga) electrode in the negative direction, which suggests that chemisorbed DMSO dipoles are oriented with their negative (oxygen) ends to the metal surface. It is found that the solvent chemisorption potential drop on the (Cd Ga) electrode increases in the series AN < GBL < DMF < DMSO, i.e. with increasing donor number of the solvent. The energy of metal–DMSO chemisorption interaction increases in the series (Tl Ga) < (Cd Ga) ≈ (In Ga) < Ga, i.e. with an increase in the electron work function. These results indicate the donor-acceptor nature of the metal-solvent chemisorption interaction in the Helmholtz layer, where the solvent molecules are donors of the electron pair relative to the metal. In spite of a decrease in the electron work function when passing from (In Ga) to (Cd Ga), the energies of their chemisorption interaction with DMSO are close. This result can be explained by a closer approach of DMSO dipoles to the surface of the (Cd Ga) electrode as compared with the (In Ga) electrode. It contributes to a more efficient overlapping of the donor-acceptor levels of the solvent and metal during their chemisorption interaction. Based on the PZC shifts observed in 0.1 М LiCl, LiBr and LiI solutions with respect to the PZC in the solution of surface inactive electrolyte, the adsorbability of halide ions on the (Cd Ga)/DMSO interface is studied. It is shown that on the (Cd Ga)/DMSO interface, the adsorption of halide ions increases in the sequence Cl− < Br− < I−, whereas at the Hg/DMSO and Bi/DMSO interfaces, an opposite row of surface activity for these ions is observed. Unlabelled Image • (Cd Ga)–solvent interaction grows in the series AN

There has been a continuing interest in finding ways to shrink the dimensions of electronic devices, especially active devices like transistors, down to become compatible with the ever decreasing size scales, using fabrication processes such as at Intel, with the trend toward 10 nm. Eventual gate length in MOSFETs is roughly half this dimension. This had been one of the (not the only one) of interests in using ferroelectric (FE) materials in the gate of FETs, for example, when the FE material displays a negative polarization effect. Such ideas as escaping the Boltzmann tyranny have loomed large, regarding the subthreshold voltage, and have motivated this interest. It is generally understood that for stable, steady state operation of devices typical of microwave and millimeter wave electronics, no negative differential capacitance is possible with conventional thinking. However, it may be possible, perhaps in transient regions of the hysteretic curve, with strain engineering of materials, to obtain some if not all elements of the differential capacitance tensor which are negative. The analysis is based upon analyzing the physics using thermodynamic phenomenological free energy. [ABSTRACT FROM AUTHOR]

• Structure and dynamics at the electrode interface of ILs have been studied by ESHG. • Transient ESHG has revealed ultraslow relaxation of EDL structure in ILs. • ESHG signal in equilibrium shows camel-shaped capacitance behavior, specific to ILs. Electrochemical second harmonic generation (ESHG) has been applied as a probe of the slow dynamics in the electric double layer (EDL) at the ionic liquid (IL)/Au interface. When the electrode potential was stepped, the SHG signal from the interface was relaxed on the time scale longer than tens of seconds, which is distinctively slower than the RC time constant of the cell. This ultraslow relaxation in ESHG was quantitatively analyzed and discussed for several ILs, revealing that the ultraslow relaxation itself is a common phenomenon for the EDL in the ILs studied but the asymmetry of the time constants to the potential-step directions depends on the IL ions, which is likely to reflect the structure ordering of the interfacial ionic layer in the EDL depending on both ILs and the potential. The EDL structure in equilibrium has also been investigated via SHG measurements with a potential scan at a sufficiently slow rate; the potential dependence of the SHG signal was found to deviate from a simple parabolic one, reflecting the camel-shaped static differential capacitance for the EDL in ILs. [ABSTRACT FROM AUTHOR]

The capacitance of Lithium-ion Capacitors (LiCs) highly depends on their terminal voltage. Previous research found that it varies in a nonlinear manner with respect to the voltage. However, none of them modeled the capacitance evolution while considering the physicochemical phenomena that happen in a LiC cell. This paper focuses on developing a new capacitance model that is based on the Stern model of the electrochemical double layer capacitance. The model accounts for the asymmetric V-shape of the C(V) curve, which reflects the variation of the capacitance with respect to the voltage. The novelty of this study concerns the development of a model for LiCs that relies on the fundamental theory of Stern for the differential capacitance. The basic model of Stern is modified in order to account for the hybrid physicochemical structure of LiCs. Moreover, the model was applied to three aged cells to which accelerated calendar aging tests were applied at three voltage values: 2.2, 3 and 3.8 V. A drift of the voltage corresponding to the minimum capacitance was detected for the aged cells. This voltage is related to the neutral state of the positive electrode. The main cause of this phenomenon concerns the loss of lithium ions from the negative electrode of a LiC. In addition, capacitance values decreased after aging, showing an eventual blocking of the pores of the positive electrode. Therefore, the analysis of the C(V) curve was found to be an interesting tool for the interpretation of aging mechanisms.

Parameters that characterize the electric double layer structure on a renewable liquid (Cd-Ga) (0.3 at % Cd) electrode in solutions of surface-inactive electrolytes in a solvent with the low donor number, namely, acetonitrile (AN), are obtained. For the (Cd-Ga) electrode in AN, the following parameters: the potential of zero charge (PZC) unaffected by specific adsorption of ions, the value of "corrected electrochemical work function," and the potential drop due to chemisorption of solvent, are obtained and compared with analogous results at Hg/AN, Ga/AN, (Cd-Ga)/gamma-butyrolactone (GBL), and (Cd-Ga)/dimethylformamide (DMF) interfaces. The AN chemisorption shifts the potential in the negative direction, which suggests that chemisorbed AN dipoles are oriented with their negative (nitrogen) ends to the metal surface. It is demonstrated that the solvent chemisorption potential drop on the (Cd-Ga) electrode increases in the series AN < GBL < DMF, i.e., with the increase in solvent's donor number. The energy of chemisorption interaction metal-AN increases when going from (Cd-Ga) to Ga, i.e., with the increase in the work function. Based on the PZC shifts observed in 0.1 М LiBr and LiI solutions with respect to the PZC in solution of a surfaceinactive electrolyte, the adsorbability of halide ions on the (Cd-Ga)/AN interface is studied. The close values of the adsorption potential shift are obtained for Br- and I- ions, which suggests the stronger (Cd-Ga)-Br- interaction as compared with (Cd-Ga)-I-. [ABSTRACT FROM AUTHOR]

Abstract Grand canonical Monte Carlo results are reported for an electric double layer formed by a planar electrode and spherical ions. The non-electrostatic interactions are the soft interactions approximated by the Lennard-Jones (LJ) potential. In particular, the ion-ion interactions are described by the 12-6 LJ potential, while the ion-electrode interactions are given by the 9-3 potential. The ion charge is located at the centre of a sphere. Ions are immersed in a continuous dielectric medium whose relative permittivity is equal to that of a solvent. The results of simulations for a 1:1 electrolyte and the same ion diameters show that the singlet distribution function of counter-ions has a single high maximum, while that of co-ions has two small maxima. The maxima of counter- and co-ions increase with increasing ion-ion or ion-electrode soft interactions, with decreasing temperature or electrolyte concentration. Analogous changes in the soft interactions, temperature and electrolyte concentration lead to formation at some distance from the negatively charged electrode surface of a negative minimum of the integrated charge, which indicates the overscreening or charge reversion effect. They also transform the shape of differential capacitance curve from that having a maximum (bell-like shape) at the point of zero charge to that showing a minimum surrounded by maxima (camel-like shape). Difference in ion charges or in ion diameters introduce asymmetry in the shape of differential capacitance curves. Increase in a counter-ion charge (the absolute value) or decrease in their diameters elevate the electric double layer capacitance. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is employed to study graphene supercapacitors. Four different ionic liquids are considered as an electrolyte, each of which is combination of the same cation 1-ethyl-3-methylimidazolium([emim] + ), and different, cyano-containing anions, thiocyanate ([SCN] – ), dicyanamide ([N(CN) 2 ] – ), tricyanomethanide ([C(CN) 3 ] – ), and tetracyanoborate ([B(CN) 4 ] – ), respectively. In particular we investigate how electric double layer structure and electrical properties are affected by the structure of cyano containing anions. Cations and anions make alternating structure near charged electrode. Differential capacitances in four ionic liquids are found to have a maximum value at negative potential. The maximum capacitances are comparable to each other, but the corresponding potential shifts to the negative side as more cyano groups are attached to the anion. Starting from the interfacial layer, the effects of the further ionic layers on differential capacitance are systematically investigated. Comparing charges of the electrode and those of ionic layers, we find that differential capacitance behavior mainly stems from the ion exchange between electric double layer and bulk region. The ion exchange behaviors are decomposed into cation and anion contributions. The differential charging mechanisms of the system are strongly dependent on the electric potential. The maximum capacitances are consequence of rapid desorption of respective anions. [ABSTRACT FROM AUTHOR]

We propose and develop a classical density functional theory for the description of a minor amount of water dissolved in ionic liquid in the vicinity of an electrode. In addition to the electrostatic energy and lattice-gas mixing entropy terms, the utilised grand canonical potential contains several phenomenological terms/parameters that describe short-range interactions between ions, water molecules and the electrode. Here we investigate: (i) specific interaction of ions and molecules with the electrode, which are responsible for their specific adsorption; (ii) hydrophilicity/hydrophobicity of ions. We obtain water electrosorption isotherms as a function of the potential drop across the electrical double layer, investigate its asymmetry with respect to the sign of electrode potential, and establish the relationship between the sign of this asymmetry and hydrophobicity/hydrophilicity of cations and anions. We also calculate the effect of water electrosorption on the double layer differential capacitance which brings clear new features to its voltage dependence, some of which have been already experimentally observed. [ABSTRACT FROM AUTHOR]

The temperature dependence of room temperature ionic liquids differential capacitance is studied here with both theoretical and computational methods. On the theory front, the lattice-gas mean-field theory of ionic liquids is further generalised to account for ‘ion pairing’ and ‘neutral aggregate’ formation. An anomalous temperature dependence of linear response capacitance was found, similar to that reported in earlier work. The theory also predicted that differential capacitance curves transform from a camel to bell shape with increasing temperature. Molecular dynamics simulations verified the expected transition in shape of differential capacitance curves with temperature and the dependence of linear response capacitance on temperature. Further investigation into charge density distributions revealed an ordered structure, reminiscent of oriented ion pairs and neutral aggregates, extending far enough from the electrode to control the capacitance-voltage response. It was found that these structures were dismantled with increasing temperature, as predicted by the mean-field theory. [ABSTRACT FROM AUTHOR]

Selecting the most suitable force field is a key to meaningful molecular dynamics (MD) simulation. To select the appropriate gold force field to model the Au(111)/ionic liquid interface, a systematic comparison of four different widely used force fields of gold and a typical carbon force field has been studied by MD simulations with constant potential method. We calculated the ion adsorption behavior and differential capacitance of interfaces between the gold electrode and ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PYR][TFSI]) in comparison with the experimental results and showed the effects on the solid-liquid interfaces from the van der Waals interaction, image force effect and cumulative ions. Based on the comparison between the results of simulations and experiments, we recommend two types of force fields to properly model the Au(111)/ionic liquid interfaces. [ABSTRACT FROM AUTHOR]

Evolution from fossil fuel energy to renewable energy sources and technologies is in the spotlight towards an accelerated energy transition process. One of the challenges of the intermittent renewable energy production is related to the existence of an appropriate energy storage technology in order to effectively use the renewable energy generated. Electrochemical energy storage devices rely on the key property of the electrical double layer integral capacitance. The use of mixed ionic liquids can be an effective strategy to increase the performance of electric double layer capacitors. Here, the studies on the interfacial behaviour of ionic liquids mixtures containing a common ion for a model mercury/ionic liquid interface are reported. Enhancement of the differential capacitance, nearly 3 times higher compared to ILs in the pure state, was achieved by an appropriate combination of ion size both in cation and the anion and asymmetry. The results are interpreted as a consequence of surface voids occupation and by the accumulation of more counter ions and displacement larger anion by the smaller anion in the mixture. [ABSTRACT FROM AUTHOR]

Many theoretical and experimental studies have been focused on the physicochemical properties of dense ionic fluids such as ionic liquids (ILs). However, less attention has been given to interfacial properties involving deep eutectic solvents (DES). The impact of the DES composition, hydrogen bond donor (HBD) structure, temperature, and electrode nature material on the DES-electrode vertical interactions remain vague. The lack of knowledge imposes significant constraints in proposing a suitable Electrical Double Layer model (EDL) to describe the DES at electrified interfaces. Measuring differential capacitance-potential curves is a strategy to assess the EDL structure and understand how ions interact with the electrode surface, which knowledge is fundamental to designing and optimizing electrochemical systems for various applications (e.g. , energy storage devices). Accordingly, a set of choline chloride-based DESs was assessed containing distinct HBD at their eutectic composition (the polyalcohol's 1,2-ethanediol, 1,2-propylene glycol, 1,3-propylene glycol, and the amide urea) against glassy carbon (GC), gold (Au), and the platinum (Pt) electrode at different temperatures. The differential capacitance-potential curves were found to vary significantly in shape in the three different electrode surfaces studied, ranging from camel shape (Au electrode), U-shape (GC), and asymmetric bell shape (polycrystalline Pt). The carboxylic malonic and oxalic acids were also assessed for a proper comparison to understand better the role of the HBD's functional group in shaping the electrode-electrolyte structure against the trend found with diol isomers. A suitable EDL model must inevitably accommodate interfacial properties assessed at the capacitive region, namely the influence of the surface chemistry, potential dependence, DES structure molecules, and temperature in shaping the electrified interfacial anatomy. [ABSTRACT FROM AUTHOR]

Atomistic molecular dynamics simulations on electrochemical interfaces are often required to be performed at a desired electrode potential. We show an iterative use of a constant-voltage molecular dynamics method is effective for its realization. It can locate the electrode potential to target values within 0.02 V accuracy. The differential capacitance of a double-layer capacitor is obtained as a function of the electrode potential in a well regularized manner. We also demonstrate an impact of a parameter for a metal electrode model on the differential capacitance, indicating a large contribution of the metal surface polarization to interfacial properties. [Display omitted] • A scheme for MD simulations on electrochemical interfaces is presented. • Equilibrium simulations can be performed at desired electrode potentials. • A differential capacitance is calculated in a regularized manner. • Interfacial water reorientation correlates well with the differential capacitance. • Metal electrode surface polarization impacts interfacial properties. [ABSTRACT FROM AUTHOR]

We propose calculating the differential capacitance (DC) of a two-island system (2IS) in terms of the expectation values of the winding numbers of the phase configurations. The quantum Monte Carlo (QMC) method was used to produce the results, which showed that at low temperatures, where the Coulomb blockade (CB) effect occurs, the DC of the system was dependent on the two gate voltages. However, the DC becomes a constant at high temperatures, where the CB effect disappears. Since the maximal DC was determined, the position of the triple point, which exhibits a 2IS characteristic, was thus identified. In addition, we compared the findings with the linear response conductance experiment in terms of the visibility parameter to determine the strength of the CB effect. • The differential capacitance of the two-island system was proposed. • The differential capacitance perfectly describes the Coulomb blockade effect.. • The visibility was calculated from the differential capacitance data. [ABSTRACT FROM AUTHOR]