Properties Of Double Layer Research Articles

Nanoporous Hollow Carbon Spheres Derived from Fullerene Assembly as Electrode Materials for High-Performance Supercapacitors

The energy storage performances of supercapacitors are expected to be enhanced by the use of nanostructured hierarchically micro/mesoporous hollow carbon materials based on their ultra-high specific surface areas and rapid diffusion of electrolyte ions through the interconnected channels of their mesoporous structures. In this work, we report the electrochemical supercapacitance properties of hollow carbon spheres prepared by high-temperature carbonization of self-assembled fullerene-ethylenediamine hollow spheres (FE-HS). FE-HS, having an average external diameter of 290 nm, an internal diameter of 65 nm, and a wall thickness of 225 nm, were prepared by using the dynamic liquid-liquid interfacial precipitation (DLLIP) method at ambient conditions of temperature and pressure. High temperature carbonization (at 700, 900, and 1100 °C) of the FE-HS yielded nanoporous (micro/mesoporous) hollow carbon spheres with large surface areas (612 to 1616 m2 g-1) and large pore volumes (0.925 to 1.346 cm3 g-1) dependent on the temperature applied. The sample obtained by carbonization of FE-HS at 900 °C (FE-HS_900) displayed optimum surface area and exhibited remarkable electrochemical electrical double-layer capacitance properties in aq. 1 M sulfuric acid due to its well-developed porosity, interconnected pore structure, and large surface area. For a three-electrode cell setup, a specific capacitance of 293 F g-1 at a 1 A g-1 current density, which is approximately 4 times greater than the specific capacitance of the starting material, FE-HS. The symmetric supercapacitor cell was assembled using FE-HS_900 and attained 164 F g-1 at 1 A g-1 with sustained 50% capacitance at 10 A g-1 accompanied by 96% cycle life and 98% coulombic efficiency after 10,000 consecutive charge/discharge cycles. The results demonstrate the excellent potential of these fullerene assemblies in the fabrication of nanoporous carbon materials with the extensive surface areas required for high-performance energy storage supercapacitor applications.

High stability asymmetric supercapacitor cell developed with novel microwave-synthesized graphene-stabilized ruthenium antimonide nanomaterial

Ruthenium antimony oxide (RuSbO), and ruthenium antimony oxide graphene (RuSbO-G) nanomaterial was synthesized via the microwave-assisted method for the first time and tested as a possible electrode material for an asymmetric supercapacitor device. The formation of the nanocomposites was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images where the RuSbO material showed randomly distributed spherically shaped nanoparticles, and the RuSbO-G showed ruthenium and antimony nanoparticles scattered randomly on the graphene sheets. The SEM-electron dispersion X-ray spectroscopy (SEM-EDS) showed significant proof for nanoparticle formation with the elemental composition, while the X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Both materials were further characterized in a three-electrode cell setup using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) and their electrochemical properties were compared to establish their suitability for energy storage purposes. From the result, different double layer properties were shown by the RuSbO and RuSbO-G in the 1 M Li2SO4 electrolyte. When compared to the RuSbO electrode, the composite had greater energy storage capabilities with a maximum capacitance of 289.47 F g−1 at 0.1 A g−1 current load. An efficiency of ~100 % was reached at a current density of 0.5 A g−1. Subsequently, both materials were used to fabricate a portable asymmetric supercapacitor. The RuSbO-G device yielded a maximum specific capacitance of 167.96 F g−1, resulting in an energy density of 75.58.0 W h kg−1 at a power density of 360 W kg−1 at 0.1 A g−1 current load, with ~100 % charge retention after 4900 cycles. This study turns a new research light on RuSbO based materials as an energy storage material for supercapacitors.

Investigation of Different Aqueous Electrolytes for Biomass-Derived Activated Carbon-Based Supercapacitors

The present work reports the synthesis of biomass derived activated carbon and its electrochemical behaviour in different electrolytes. Ricinus communis shell (RCS) was used as a raw material in this study for the synthesis of activated carbon (AC) following a high-temperature activation procedure using potassium hydroxide as the activating agent. The physical and structural characterization of the prepared Ricinus communis shell-derived activated carbon (RCS-AC) was carried by Brunauer-Emmett-Teller analysis, X-ray diffraction analysis, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and Scanning Electron Microscopy. The synthesized AC was electrochemically characterized using various techniques such as Cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) tests, and Electrochemical impedance spectroscopy (EIS) measurements in different aqueous electrolytes (KOH, H2SO4, and Na2SO4). The results show that the double layer properties of the RCS-AC material in different electrolytes are distinct. In specific, the working electrode tested in 3 M KOH showed excellent electrochemical performance. It demonstrated a specific capacitance of 137 F g−1 (at 1 A g−1 in 3 M KOH) and exhibited high energy and power densities of 18.2 W hkg−1 and 663.4 W kg−1, respectively. The observed capacitance in 3 M KOH remains stable with 97.2% even after 5000 continuous charge and discharge cycles, indicating long-term stability. The study confirmed that the synthesized RCS-derived activated carbon (RCS-AC) exhibits good stability and physicochemical characteristics, making them commercially promising and appropriate for energy storage applications.

The properties of electric double layer at activated carbon surface and their effect on gold and silver adsorption from cyanide solutions

This paper looks at the properties of electric double layer (EDL) found at the surface of activated carbons. The study relied on the electrical conductivity method, which is based on simultaneous use of polarization dependences at direct current and conductometric measurements at alternating current. It was found that the adsorption of gold and silver intensifies in the anode region of carbon surface polarization. Two regions with peak adsorption were identified in the following ranges of potentials: +0.2÷+0.25 and +0.6÷+0.8 V. EDL diffusion helps improve the environment for the adsorption of cyanide complexes of gold and silver by active centres of the adsorbent surface. The authors believe that an increased mass transfer in the first range of potentials can be attributed to a decreased diffusion resistance caused by changed zero charge polarity, while in the second range of potentials it can be attributed to the cyan-ion oxidation reaction and an easier access of the negatively charged cyanide complexes of gold and silver to the positively charged surface of the carbon adsorbent. The polarization dependences by direct current in the anode region tend to monotonously rise, which is indicative of a lower EDL density, an increased conductivity at the adsorbent surface/solution boundary and improved adsorption conditions. Graphs showing a relationship between alternating current and carbon adsorbent potential helped determine maximum conducti vity values, which almost match the peak values of gold and silver adsorption. The authors established that the adsorbent’s potential has a significant effect on the activated carbon adsorption of cyanide complexes of gold and silver. The use of the electrical conductivity method for examining the EDL helps explain certain features typical of the activated carbon adsorption of gold and silver from cyanide solutions.

Properties of electrolyte near rough electrodes: Capacity and impedance

The properties of the electric double layer (EDL) are essential for various fields of science and technological applications. In this short review, I discuss the publications devoted to investigating the behavior of electrolyte in contact with rough electrodes. Since the EDL is formed at the electrolyte-electrode interface, the surface geometry directly affects ion distributions. Key effects of rough electrodes are a significant increase in the accumulated charge; a change in the dependence of the differential capacitance on the applied potential; and a constant phase element contribution to the impedance. Finally, I highlight the limitations of existing approaches and suggest possible solutions for improvement.

Engineering oxygen functional groups in reduced graphene oxide for use in high‐performance flexible supercapacitors

Graphene-based flexible supercapacitors (FSCs) are promising energy-storage devices that can potentially power the next generation of wearable and portable electronics owing to their high-power densities, quick charging/discharging rates, and excellent cycle lives. The manufacture of FSC devices with extended potential windows can help increase their energy density. However, the poor reaction kinetics of graphene (which has electric double-layer capacitive properties) can lead to low energy densities. In this study, graphene nanosheets with different oxygen contents are fabricated on a flexible carbon cloth substrate through thermal treatments in an argon atmosphere. The effects of the degree of disorder, surface area, and oxygen moieties on the supercapacitive properties of the nanosheets are explored systematically. Graphene oxide electrodes reduced at 300°C are used as the cathode and anode, and they exhibit large areal capacitances of 82.7 and 324.4 mF cm−2, respectively, at 4 mA cm−2. When the proposed device is used as a symmetric FSC cell, the electrode exhibits an excellent areal capacitance (70.3 mF cm−2 at 1 mA cm−2) and long cycle life in the 0 to 1.4 V voltage window. Furthermore, the FSC cell has a maximum energy density of 19.1 μW h cm−2 at a power density of 0.69 mW cm−2.

Electrochemically tracking interactions between molecular ions of sodium dodecyl sulphate and the selected amino acid at the electrode-electrolyte interface

Surfactant assisted electrode–electrolyte (E-E) interface is a fascinating research topic that has been employed in different fields such as biosensing, energy devices, surface technology, etc. This work explores the electrochemical properties of sodium dodecyl sulphate (SDS) in the presence of essential amino acid (AA) i.e., l-Threonine (THR), dl-Methionine (MET), and l-Phenylalanine (PHE) at the E-E interface through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For the electrochemical study of SDS at its premicellar and post micellar concentration in presence of AA ions, the three-electrode configuration consisting of glassy carbon (GC) as the working electrode, Ag/AgCl as reference electrode, and Pt wire as the counter electrode, have been used. Briton Robinson buffer (pH, 2) was utilized as the supporting electrolyte. The effect of AA ions on faradic properties of electroactive ions in the SDS system was studied by CV measurement. The scan rate effect was used to calculate the kinetic parameters such as maximum surface adsorbed concentration (Г, mol/cm2), diffusion coefficient (D, cm2/s), and capacitance of electrode surface (C, F/cm2). EIS measurements were applied to study the capacitive and resistive properties of the electric double layer (EDL) that developed at the E-E interface. The double-layer capacitance (Cdl) of EDL was extracted from the equivalent circuit diagram. The results from electrochemical measurements suggested that the electrochemical properties of SDS such as the faradaic process of electroactive ions and their kinetics through the SDS channel and charge storage performance of electrified surface were strongly affected by AA ions at the E-E interface through electrostatic interactions between oppositely charged ions. This work contributed to the understanding of the electrochemical interaction of biomolecular ions at the surfactant-assisted E-E interface. It will diversify the application of surface-active agents in biology and biotechnology.

Tuning Ionic Screening To Accelerate Electrochemical CO2 Reduction in Ionic Liquid Electrolytes

Electric double layer formation often governs the rate and selectivity of CO2 electrochemical reduction. Ionic correlations critically define double layer properties that are essential to electrocatalytic performance, including capacitance and localization of potential gradients. However, the influence of ionic correlations on CO2 electroreduction remains unexplored. Here, we use electrochemical conversion of CO2 to CO in ionic liquid-based electrolytes to investigate how the emergence of ionic correlations with increasing ion concentration influences reaction rates and selectivity. Remarkably, we find substantial acceleration of potential-dependent CO2 reduction rates and enhancement of faradaic efficiency to CO at intermediate concentrations of 0.9 M ionic liquid in acetonitrile, a concentration regime that has not been studied previously. We find that onset potentials for CO2 reduction remain relatively unchanged at −2.01 V vs Ag/Ag+ from 0.025 M up to 1.1 M and increase to −2.04 V vs Ag/Ag+ in the limit of neat ionic liquids. Hence, the acceleration of CO2 reduction we observe originates from the amplification of potential-dependent driving forces, as opposed to changes in onset potential. Importantly, our findings are general across cocatalytic and noncatalytic ions. We propose that concentrations of maximum reactivity correspond to conditions where electric double layers exhibit the strongest screening, which would localize electric fields to stabilize polar intermediates. Our study demonstrates that tuning bulk electrostatic screening lengths via modulation of ionic clustering provides a general approach to accelerating both inner-sphere and outer-sphere electrochemical reactions.

(Keynote) Deciphering Electrocatalytic Reactions with Theory and Computation: The Case of CO2 Reduction

The interfacial region between metal surface and aqueous electrolyte is of central importance for electrochemical reactions. The need to understand the properties of this electrochemical double layer (EDL) region drives extensive research.1,2 A foremost goal of research in electrocatalysis is the development of a theoretical-computational framework. The fundamental task for such a framework is to unravel the complex interplay of electronic structure effects of the catalyst material, potential-induced variations of the chemisorption state, local reaction conditions on the electrolyte side, and electrochemical kinetics of reactions of interest. A recently developed theoretical approach revealed the non-monotonic charging behaviour of a Pt electrode3 and it was thereafter used to decipher the oxygen reduction reaction.4 In the present work, we adapt this approach to study how the local reaction environment dictates the mechanism and kinetics of reduction to CO at an Ag electrode. Our hierarchical model accounts for the multistep reaction kinetics of surface reactions, local chemical equilibria (involving CO2, HCO3 -, CO3 2-, OH-, H+), the specific surface charging state at a given electrode potential, solvent polarization and ion density variations, and reactant/product transport. It integrates interface and pore-level models to account for this interplay. The combined approach rationalizes the impact of the considered effects on the kinetics of the reaction, manifested experimentally in changes of the effective Tafel slope as a function of electrode potential. Lateral interactions between chemisorbed species are seen to contribute to the decrease of the CO current density at high electrode potentials, in addition to mass transport effects, surface charging effects and pH increase. We will conclude with a discussion of the parameters that allow tuning the local reaction environment and thus the electrocatalytic activity and selectivity of the electrocatalyst. 1O.M. Magnussen and A. Gross, Toward an Atomic-Scale Understanding of Electrochemical Interface Structure and Dynamics, J. Am. Chem. Soc. 141, 4777–4790 (2019). 2M.J. Eslamibidgoli and M.H. Eikerling, Approaching the Self-consistency Challenge of Electrocatalysis with Theory and Computation, Current Opinion in Electrochemistry 9, 189-197 (2018). 3J. Huang, A. Malek, J. Zhang and M.H. Eikerling, Non-monotonic Surface Charging Behavior of Platinum: A Paradigm Change, J. Phys. Chem. C 120, 13587-13595 (2016). 4J. Huang, J. Zhang and M. Eikerling, Unifying Theoretical Framework for Deciphering the Oxygen Reduction Reaction on Platinum, Phys. Chem. Chem. Phys. 20, 11776-11786 (2018).

Thermodynamics of electrolyte solutions near charged surfaces: Constant surface charge vs constant surface potential.

Electric double layers are ubiquitous in science and engineering and are of current interest, owing to their applications in the stabilization of colloidal suspensions and as supercapacitors. While the structure and properties of electric double layers in electrolyte solutions near a charged surface are well characterized, there are subtleties in calculating thermodynamic properties from the free energy of a system with charged surfaces. These subtleties arise from the difference in the free energy between systems with constant surface charge and constant surface potential. In this work, we present a systematic, pedagogical framework to properly account for the different specifications on charged bodies in electrolyte solutions. Our approach is fully variational-that is, all free energies, boundary conditions, relevant electrostatic equations, and thermodynamic quantities are systematically derived using variational principles of thermodynamics. We illustrate our approach by considering a simple electrolyte solution between two charged surfaces using the Poisson-Boltzmann theory. Our results highlight the importance of using the proper thermodynamic potential and provide a general framework for calculating thermodynamic properties of electrolyte solutions near charged surfaces. Specifically, we present the calculation of the pressure and the surface tension between two charged surfaces for different boundary conditions, including mixed boundary conditions.

Dual In Situ Laser Techniques Underpin the Role of Cations in Impacting Electrocatalysts.

Understanding the electrode/electrolyte interface is crucial for optimizing electrocatalytic performances. Here, we demonstrate that the nature of alkali metal cations can profoundly impact the oxygen evolution activity of surface‐mounted metal–organic framework (SURMOF) derived electrocatalysts, which are based on NiFe(OOH). In situ Raman spectroscopy results show that Raman shifts of the Ni−O bending vibration are inversely proportional to the mass activities from Cs+ to Li+. Particularly, a laser‐induced current transient technique was introduced to study the cation‐dependent electric double layer properties and their effects on the activity. The catalytic trend appeared to be closely related to the potential of maximum entropy of the system, suggesting a strong cation impact on the interfacial water layer structure. Our results highlight how the electrolyte composition can be used to maximize the performance of SURMOF derivatives toward electrochemical water splitting.

Dual In Situ Laser Techniques Underpin the Role of Cations in Impacting Electrocatalysts

AbstractUnderstanding the electrode/electrolyte interface is crucial for optimizing electrocatalytic performances. Here, we demonstrate that the nature of alkali metal cations can profoundly impact the oxygen evolution activity of surface‐mounted metal–organic framework (SURMOF) derived electrocatalysts, which are based on NiFe(OOH). In situ Raman spectroscopy results show that Raman shifts of the Ni−O bending vibration are inversely proportional to the mass activities from Cs+ to Li+. Particularly, a laser‐induced current transient technique was introduced to study the cation‐dependent electric double layer properties and their effects on the activity. The catalytic trend appeared to be closely related to the potential of maximum entropy of the system, suggesting a strong cation impact on the interfacial water layer structure. Our results highlight how the electrolyte composition can be used to maximize the performance of SURMOF derivatives toward electrochemical water splitting.

Impact of porosity on the structural and optoelectronic properties of nanoporous GaN double layer fabricated via combined electrochemical and photoelectrochemical etching

Nanoporous GaN double layer structures with porosity ranging from 10% to 60% are fabricated via a combined electrochemical etching and photoelectrochemical etching process. The porosity as well as the variation in the size and shape of the nanopores are controlled by regulating the applied voltage in the etching process. With the increase in the porosity, the biaxial stress and reflectance index of the nanoporous GaN double layer decrease from 0.74 GPa and 2.4 to 0.42 GPa and 2.0, respectively. Furthermore, the photoluminescence intensity of the InGaN/GaN multi-quantum wells grown on the nanoporous GaN is approximately three times higher than that on the as-grown reference GaN. The enhanced photoluminescence intensity can be attributed to the porosity controlled through the incorporated nanopores, which increase the light extraction efficiency. The light generated in the active layer is further extracted due to scattering by the nanopores.

Coexistence of antiferromagnetism and superconductivity in Mn/Nb(110)

We report on the structural and magnetic properties of single and double atomic layers of Mn on a clean and unreconstructed Nb(110) substrate. Low-temperature scanning tunneling spectroscopy measurements reveal a proximity-induced superconducting state in the Mn thin films, which are found to grow pseudomorphically on the Nb surface. Spin-polarized scanning tunneling microscopy measurements reveal a c(2x2) antiferromagnetic order in the Mn layers, with an out-of-plane spin-orientation. First-principles density functional theory calculations confirm the experimentally observed magnetic state, which is understood as the consequence of a strong intra- and inter-layer nearest-neighbor antiferromagnetic exchange coupling. These results are expected to be of importance for the design and the investigation of novel superconducting antiferromagnetic spintronic systems.

Impact of Porosity on the Structural and Optoelectronic Properties of Nanoporous Gan Double Layer Fabricated Via Combined Electrochemical and Photo-Electrochemical Etching

Impact of Porosity on the Structural and Optoelectronic Properties of Nanoporous Gan Double Layer Fabricated Via Combined Electrochemical and Photo-Electrochemical Etching

Solvent-Free Soft-Template Synthesis of Highly-Ordered Mesoporous Carbons Via Self-Assembly Promoted by Mg(No3)2 and Their Electric Double-Layer Capacitance Property

Solvent-Free Soft-Template Synthesis of Highly-Ordered Mesoporous Carbons Via Self-Assembly Promoted by Mg(No3)2 and Their Electric Double-Layer Capacitance Property

Influence of Charge Lipid Head Group Structures on Electric Double Layer Properties.

In this study we derived a model for a multicomponent lipid monolayer in contact with an aqueous solution by means of a generalized classical density functional theory and Monte Carlo simulations. Some of the important biological lipid systems were studied as monolayers composed of head groups with different shapes and charge distributions. Starting from the free energy of the system, which includes the electrostatic interactions, additional internal degrees of freedom are included as positional and orientational entropic contributions to the free energy functional. The calculus of variation was used to derive Euler–Lagrange equations, which were solved numerically by the finite element method. The theory and Monte Carlo simulations predict that there are mainly two distinct regions of the electric double layer: (1) the interfacial region, with thickness less than or equal to the length of the fully stretched conformation of the lipid head group, and (2) the outside region, which follows the usual screening of the interface. In the interfacial region, the electric double layer is strongly perturbed, and electrostatic profiles and ion distributions have functionality distinct to classical mean-field theories. Based purely on Coulomb interactions, the theory suggests that the dominant effect on the lipid head group conformation is from the charge density of the interface and the structured lipid mole fraction in the monolayer, rather than the salt concentration in the system.

Pore Structures and Electric Double Layer Properties of Activated Carbon Derived from Demineralized Spent Coffee Grounds

Pore Structures and Electric Double Layer Properties of Activated Carbon Derived from Demineralized Spent Coffee Grounds

Unusual properties of the electric double layer in an extremely narrow nanotube. A grand canonical Monte Carlo and classical DFT study

A grand canonical Monte Carlo (GCMC) simulation technique at a constant electrode–electrolyte potential drop and classical density functional theory (CDFT) have been employed to study the ion distribution and the differential capacitance of an electric double layer (EDL) in extremely narrow nanotubes. In the applied constant-potential GCMC method, to preserve the electroneutrality of the system after a single ion exchange, the electrode charge is suitably modified. The resulting charge fluctuations are used to calculate the differential capacitance of the EDL. Results for the ion distributions and differential capacitance in the nanotubes are reported for symmetric +1: 1 ionic valences with a common ionic diameter of 0.4 nm at electrolyte concentrations of 0.1 m, 1.0 m, and 2.5 m, a cylinder radius of 0.6 nm, potential drop varying from −0.6 V to 0.6 V, a relative permittivity of 78.5, and a temperature of 298.15 K. These results are compared with corresponding data for size-asymmetric systems with cations of diameters of 0.32 nm and 0.48 nm and ion-valence asymmetric systems of +2: 1 and +3: 1. At higher electrode surface charges, the counter-ion density distributions show an unusual accumulation along the axis of the nanotube. Differential capacitance plots have four or fewer, often three, maxima. The central minimum surrounded by two maxima undergoes a transition from a minimum to a maximum as the electrolyte concentration is increased. The positions of the side maxima indicate the electrode potential at which the rate of the unusual counter-ion accumulation is at its highest. Comparison between the results of simulations and CDFT suggests the latter to be reliable for investigation of the electrical capacitance properties of extreme nanoscale supercapacitors, even if its degree of accuracy for particle distributions decreases with increasing surface charge.

Charge storage behavior of sugar derived carbon/MnO2 composite electrode material for high-performance supercapacitors

Herein, we present an efficient and simple method to develop a 3D-Carbon /MnO2 (C/MnO2) composite active material for high-performance supercapacitors. MnO2 nanorods are synthesized by the hydrothermal process, and corresponding carbon composite is synthesized from table sugar precursors using the combustion process. MnO2 has rod-like morphologies and forms 3D electrode architectures with carbon, and contains about 5–10 nm of carbon coating. The charge storage behavior studied by galvanostatic charge-discharge cycling shows capacitance of 416 F g−1 at 1 A g−1 with capacitance retention of 90% after 5000 cycles. The superior electrochemical performance is attributed to the one–dimensional ion transport of Mn ion, the in-situ 3D electrode architecture, and carbon coating that enhances the conductivity and the surface area of MnO2. C/MnO2 composite exhibits an energy density of 60 Wh kg−1 with a power density of 201 W kg−1. The combined pseudocapacitive behavior of MnO2 and electric double-layer capacitors property of carbon exhibits significant electrochemical performance in the aqueous electrolyte. The synthesis approach uses environment benign active materials with the low cost of electrode fabrication provides an alternative route for the development of high-performance supercapacitors.