Electrostatic Double-layer Capacitor Research Articles

Modeling of capacitance for carbon-based supercapacitors using Super Learner algorithm

Due to some specifications such as high capacitance and power density, electrostatic double-layer capacitors (EDLCs) are more noticeable than other supercapacitors. Some physical and chemical properties, surface functional groups, and testing conditions affect the efficiency and in particular the capacitance of EDLCs with carbon-based electrodes. In this study, four machine learning models, including Super Learner (SL), Extremely Randomized Trees (Extra trees), Extreme learning machine (ELM), and Multivariate adaptive regression splines (MARS) were implemented to predict the EDLCs' capacitance based on different impressive properties. A large dataset was assigned to the 121 different carbonaceous electrodes collected under various conditions, including 13 physical and chemical properties: voltage window (V), specific surface area (SSA) and SSA of micropore, pore volume (PV), and micropore volume, the ratio of D-band and G-band (Id/Ig) and doping elements (inputs parameters). The results indicated that the SL model with the R2 values of 0.9781, 0.9717, and 0.9768 for training, testing, and total dataset, respectively, and the RSME value of 18.099 was the most accurate model in comparison with the others. Indeed, the sensitivity analysis results exhibited that SSA with the relevance factor of 0.323 is the most important feature in the capacitance of carbon-based electrodes, while the presence of boron, sulfur, fluorine, phosphorus doping elements and pore size can be ignored.

Characterization of Synthesized NiCo2O4 with Trisodium Citrate for Supercapacitor Material: A Preliminary Study

Supercapacitors can be called electrostatic double-layer capacitors (EDLCs) or pseudo-capacitors based on their energy storage mechanism. Pseudo-capacitors with metal oxide electrodes that transmit electric charge offer great application power but low stability. This study aims to characterize trisodium citrate (TSC) modified NiCo2O4/rGO electrodes as a preliminary study for the NiCo2O4 nanoparticle pseudo-capacitor. The materials were characterized using SEM (Scanning Electron Microscopy), XRD (X-Ray Diffractometer), FT-Raman (Fourier Transform Raman Spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy). All of these analyses confirmed that NiCo2O4 was manufactured successfully using TSC. At XRD, the angles of 2????, namely 45.04 and 53.34°, matched the plane of the cubic phase nanorod crystals of NiCo2O4 with values of 400 and 511, respectively. In the Raman examination, the presence of rGO, which increased the crystallinity of NiCo2O4 nanoparticles, was confirmed. FTIR analysis indicated that the 1550-1600 cm−1 corresponds to a C=C functional group in an aromatic ring or a C=O ????-???? structure, and the wavenumber of 2300 cm−1 corresponds to the OH group in TSC, an alkanoate derivative. SEM analysis determined that NiCo2O4 nanoparticles with 1 mmol TSC are the ideal material for supercapacitor electrodes, as the structure is the most uniform, soft, and tidy. Further analysis is needed to confirm the stability of the modified material.

Nanocomposite electrodes using highly conductive sub-millimetre-long single-walled carbon nanotubes pasted with PEDOT:PSS and high-performance actuators

We describe new nanocomposite electrodes and actuators using highly conductive single-walled carbon nanotubes (<1 mm in length) fabricated using the ‘super-growth’ method (SG-SWCNT) pasted with poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and combined with electrostatic double-layer capacitors (EDLCs) and faradaic capacitors (FCs). The electromechanical/chemical properties of the SG-SWCNT/PEDOT:PSS/ionic liquid (IL) electrode and actuator were compared with those of the SG-SWCNT/IL electrode and actuator. The SG-SWCNT/PEDOT:PSS/EMI[C(CN)3] electrode (volume resistivity; 4.26 Ω cm, surface resistivity; 0.55 Ω/sq. and conductivity; 235 S/cm) was a more conductive electrode than the equivalent SG-SWCNT/EMI[C(CN)3] electrodes (36.0 Ω cm, 2.37 Ω/sq. and 28.0 S/cm). This is thought to be a result of the synergy between SG-SWCNT and PEDOT:PSS. The maximum strain of the SG-SWCNT/PEDOT:PSS/EMI[B(CN)4] actuator ranged from 0.39% to 1.88%, which is approximately 1.6–7.5 times larger than that of the SG-SWCNT/EMI[B(CN)4] actuator. The actions of the hybrid actuators differed from those of the SG-SWCNT/IL actuators, which function only as EDLC units. A kinetic model featuring double-layer charging successfully simulated the frequency-dependent displacement responses of both types of actuators. The use of a PEDOT:PSS polymer promotes higher conductivity, specific capacitance, and strain, which is thought to originate in synergy between SG-SWCNT and PEDOT:PSS. Thus, flexible robust films that exploit this synergy are likely to be useful as actuator components in energy conversion and wearable devices.

COMPREHENSIVE STUDY OF SUPER CAPACITOR

super capacitor or ultra-super capacitor are electrostatic double layer capacitor (ELDC) are the most promising energy device they offer greater transient response power density, low weight, low volume and low internal resistance which make them suitable for several application. This paper gives brief insight into the design characteristic and application of supercapicator. Keywords: - Electrolyte, activated carbon, super capacitor.

Pyrazine-based organic electrode material for high-performance supercapacitor applications

Pseudocapacitors (PCs) exhibit high capacitance and high energy density, which renders incredible execution in energy storage gadgets. PCs bridge the gap between batteries and electrostatic double-layer capacitors (EDLCs). Herein, we designed novel electrode material i.e. naphtho[2,3-h]naphtho[2′,3′:5,6]quinoxalino[2,3-a]naphtho[2′,3′:5,6]quinoxaline [2,3-c]phenazine-5,12,17,22, 27,30-hexaone (Pyz-ANQ) composed of hexaketocyclohexane (HKCH) and 2,3-diaminoanthraquione (ANQ) subunits. The Pyz-ANQ electrode has been fabricated on a Toray carbon paper (CP) and used as a pseudocapacitor electrode which showed efficient pseudocapacitor performance in a three-electrode configuration. The specific capacitance (Csp) by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis are 85.2 F g−1 at a scan rate of 5 mV s−1 and 43.1 F g−1 at current density 0.5 A g−1 in 1 M H2SO4, respectively. The PCs behavior is attributed to the reversible redox chemistry of Pyz-ANQ. Furthermore, we fused the material into a symmetric solid-state two-electrode supercapacitor (SSSC) device for practical demonstration of its potential in future energy storage applications and it shows the Csp value by two methods CV and GCD such as 52.5 F g−1 @ 5 mV s−1 and 36.6 F g−1 @ 0.5 A g−1, as well as it shows excellent cyclic performance in three-electrode and two-electrode system in the percentage of 78.8% and 75.9% for 2000 GCD cycles. Significantly, Pyz-ANQ/CP electrode has an energy density of 2.6 Wh kg−1 at 4.7 kW kg−1 of power density, respectively. In this way, by utilizing HKCH and ANQ in the redox system, Pyz-ANQ/CP results in pseudocapacitive energy storage, bringing a new dimension to improve the chemistry of organic supercapacitors.

High-performance TEMPO-oxidised cellulose nanofibre/PEDOT:PSS/ionic liquid gel actuators

In a previous study that the authors have conducted, actuators based on cellulose nanofibre/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/ionic liquid (CNF/PEDOT:PSS/IL) gel electrodes and CNF/IL gel electrolytes could not be fabricated due to poor adhesion between the electrode and electrolyte layers. However, in this study, a series of novel actuators were developed using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidised cellulose nanofibre (TOCN)/PEDOT:PSS/IL gel electrode with a TOCN/IL or poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF(HFP)/IL) gel electrolyte due to good adhesion between the electrode and electrolyte layers. The TOCN/PEDOT:PSS/IL gel electrode actuators exhibited high strain performance. These actuators mainly operated via an electrostatic double-layer capacitor mechanism, with a redox capacitor mechanism making a relatively small contribution. The TOCN/PEDOT:PSS/IL gel electrode actuators showed frequency-dependent displacement responses, and a model of double-layer charging kinetics considering the combined resistance of the gel electrode/electrolyte successfully simulated the experimental results. The development of electrodes with excellent electrical conductivity (PVdF(HFP)/IL electrolytes) and electrodes/electrolytes with excellent electrical and ionic conductivities (TOCN/IL gel electrolytes) will facilitate the optimisation of the performance of TOCN/PEDOT:PSS/IL-based polymer actuators. These flexible films will be applicable for the development of actuator materials for use in wearable and transparent electronic and energy conversion devices.

A Two-Electrode, Double-Pulsed Sensor Readout Circuit for Cardiac Troponin I Measurement

This paper presents a pulse-stimulus sensor readout circuit for use in cardiovascular disease examinations. The sensor is based on a gold nanoparticle plate with an antibody post-modification. The proposed system utilizes gated pulses to detect the biomarker Cardiac Troponin I in an ionic solution. The characteristic of the electrostatic double-layer capacitor generated by the analyte is related to the concentration of Cardiac Troponin I in the solvent. After sensing by the transistor, a current-to-frequency converter (I-to-F) and delay-line-based time-to-digital converter (TDC) convert the information into a series of digital codes for further analysis. The design is fabricated in a 0.18-μm standard CMOS process. The chip occupies an area of 0.92 mm2 and consumes 125 μW. In the measurements, the proposed circuit achieved a 1.77 Hz/pg-mL sensitivity and 72.43 dB dynamic range.

Suppressed self-discharge of an aqueous supercapacitor using Earth-abundant materials

Supercapacitors (aka electrostatic double-layer capacitors — EDLCs) offer excellent power storage capacity and kinetics, but suffer under rapid self-discharge. We introduced a zeolite framework into the active capacitor electrode, with the goal to tailor the free desorption energy and thus the self-discharge rate of supercapacitors. Low-cost carbonaceous materials and benchtop production methods were used to create supercapacitor electrodes with a measured specific capacitance of 17.25 F g−1, a coulombic efficiency of 100%, and charge retention of over 25% over 24 h determined by galvanostatic charge/discharge curve measurements. This charge retention was an enhancement of ~350% compared with electrodes without zeolite coating.

Self-Standing High-Performance Transparent Actuator Based on Poly(dimethylsiloxane)/TEMPO-Oxidized Cellulose Nanofibers/Ionic Liquid Gel.

The sustainable application of cellulose nanofibers and ionic liquids (ILs) in the fabrication of transparent gel electrolyte actuators combined with thin electrodes remains to be explored. Accordingly, this study developed a new actuator on the basis of a 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers/IL/poly(dimethylsiloxane) (TOCN/IL/PDMS) transparent gel electrolyte. A casting method was employed to prepare the gel electrolyte film, and spray-coating was used to apply thin electrodes. On the basis of its electromechanical and electrochemical properties, the TOCN/IL/PDMS gel electrolyte actuator had high strain performance. The actuator's operational mechanism is based on both electrostatic double-layer capacitor (EDLC) and Faradaic capacitor mechanisms, with the EDLC mechanism having a stronger influence. The actuator's displacement-response frequency dependency was determined, and we simulated the obtained findings by using a double-layer charging kinetic model. The combined gel electrolyte and electrode resistance resulted in a favorable fit to the experimental data, as did the gel electrolyte resistance alone. The performance of the TOCN/IL/PDMS-electrolyte-based polymer actuators can be improved further by designing electrolytes (primarily) and electrodes to have high ionic and electrical conductivities. The films-which are flexible, robust, and transparent-may have potential as actuator materials within electronic and energy-conversion devices that are required to be wearable and transparent.

Effect of ruthenium on superior performance of cellulose nanofibers/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/ruthenium oxide/ionic liquid actuators

This study proposes novel actuators based on cellulose nanofibre/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/hydrous ruthenium oxide/ionic liquid (CNF/PEDOT:PSS/RuO2/IL) electrodes and the poly(vinylidene fluoride-co-hexafluoropropylene)/IL (PVdF(HFP)/IL) electrolyte, and investigates the effect of hydrous ruthenium oxide on the electrochemical and electromechanical properties of the proposed actuators. The proposed system contains an electrochemical capacitor electrode, which acts as both a faradaic capacitor (FC) and a small electrostatic double layer capacitor (EDLC). This hybrid capacitor is based on the FC (RuO2) mechanism, and a base polymer (PEDOT:PSS) and CNF skeleton replace carbon nanotubes (CNTs). Therefore, this device functions differently from traditional CNT/PVdF(HFP))/IL electrode actuators, which are only used as EDLC units, and CNF/PEDOT:PSS/IL (without RuO2) actuators, where PEDOT:PSS plays the role of both FC and base polymer. Devices built using the proposed actuators exhibit higher strains and greater maximum generated stresses than those exhibited by devices based on CNF/PEDOT:PSS/IL (i.e. without RuO2). Surprisingly, the synergism obtained by combining RuO2 and PEDOT:PSS is considerably greater than the enhancement achieved using PEDOT:PSS. The frequency dependences of the displacement responses of the CNF/PEDOT:PSS/RuO2/IL electrode actuators were then measured and successfully simulated using a double layered charging kinetic model. The developed films are novel, robust, and flexible, and they exhibit potential for use as actuator materials.

Rational Design of Electrochemical Iodine-Based Redox Mediators for Water-Proofed Flexible Fiber Supercapacitors

Flexible supercapacitors based on electrostatic double-layer capacitors as next-generation energy storage systems hold great promise for wearable and flexible electronic devices owing to their high flexibility and electrochemical cyclability. However, the challenge of low charge-storing ability still remains, as electronic devices require a high charge storage capability. As one of the advanced strategies for enhancing charge-storing ability in flexible supercapacitors, the introduction of a redox mediator (RM) into a gel electrolyte has recently attracted great interest. Here, we present a fiber-based flexible energy storage system (f-FESS) integrated with iodine-based chemical species as a novel RM, carbon fiber-based electrodes, and a solid-state polymer-gel electrolyte so as to enhance the charge storage capability of flexible supercapacitors. The as-prepared f-FESS-RM exhibits enhanced charge storage capabilities of up to 461.8 F L–1 and 64.14 mWh L–1, which are 3.6 times higher than those of f-FESS without RM. The enhanced capacitive properties of f-FESS-RM are attributed to their additional Faradic redox reaction of iodine-based chemical species in the electrolyte as well as electrical double-layer capacitive behavior. Also, the f-FESS-RM shows remarkably superior mechanical robustness under various bending, winding, knotting, and weaving conditions. Furthermore, we have demonstrated that the f-FESS-RM is stably workable under deionized water and base electrolytes. In combination, these outcomes provide a novel advanced strategy to enhance the charge-storing ability with strong mechanical robustness in flexible supercapacitors.

Temperature distribution of supercapacitors prepared by various technologies

Supercapacitors, also known by different names such as electrostatic double-layer capacitors (EDLCs) or ultra-capacitors, are electrical storage devices still in development. These devices require fast and reliable methods of assessing their state-of-health. Thermographic imaging is a method which can be applied with this aim due to its popularity, and the high negative impact of overheating on a supercapacitor’s parameters. Moreover, thermographic imaging can be easily used to identify any hot spots, present during charging and discharging while in use. These devices are comprised of porous carbon electrodes and an electrolyte, and during the charging/discharging process, extensive heat may be generated and dissipated there. We have observed temperature fluctuations and were able to identify the inhomogeneity of the tested structures. The electrical parameters (capacitance C and equivalent serial resistance ESR) were measured to determine deterioration of the specimen as requested by the industrial standard. X-ray examination of the samples was performed to identify the shape of the applied metal charge collectors. Both techniques indicated areas where eventual overheating took place due to their electrodes’ shape, suggesting their further optimisation. The proposed method is much less accurate than the calorimetric methods, determining energy flows, but is still sufficient to identify problems with heat dissipation in the developed specimens. Finally, some conclusions about the ability to apply this method in practice to monitor supercapacitors during use were presented.

Supercapacitor technology and its applications: a review

Battery technologies are well established and widely used technology but they offer several disadvantages like weight, volume, large internal resistance, poor power density, poor transient response. On the other hand, due to advancement in the material and other technology, Supercapacitor or Ultracapacitors or Electrostatic Double Layer Capacitor (EDLC) are a most promising energy storage device. They offer a greater transient response, power density, low weight, low volume and low internal resistance which make them suitable for several applications. This paper summarizes recent research and development in the field of supercapacitor technology. This paper gives a brief insight into the design, characteristics and applications of the supercapacitor.

Touch position identification based on a flexible array-less supercapacitive tactile sensor

Flexible tactile sensors with simple structures, minimal peripheral electric connections and straightforward data processing will benefit the human-machine interactions in which the contact information is crucial. However, it is still hard to balance the easy fabrication, full flexibility, large measurement area and minimal electric connection in existed tactile sensing systems. This study introduces an innovative positioning method based on a flexible supercapacitive tactile sensor. A 100 mm×100 mm prototype sensor, which contains two layers of flexible electrodes and a layer of ionic gel membrane in the middle to construct electrostatic double-layer capacitors (EDLCs), is developed to study the underlying physical principles. Following the established method, minimized electric connections are needed to achieve the mm-scale touch position/movement trace identification. Under the touch pressure, the formation of supercapacitors around the touch area leads to re-distribution of electric potential within the sensor. The electrical voltage variation is gauged at four points, and the data are calculated to estimate the touch positions following a two-step protocol. The developed method demonstrates high accuracy of position identification (around 5% in the 100 mm×100 mm flexible sensor), superior anti-disturbance capability (more than ∼104 variation of capacitance) and fast response (∼ms level). At the same time, it has no dependency on complex fabrication, redundant electric circuit or sensing unit arrays. These promising characteristics can benefit various application fields, such as intelligent robotics, biomedical devices and wearable equipment.

Designing Three-Dimensional Architectures for High-Performance Electron Accepting Pseudocapacitors.

By storing energy from electrochemical processes at the electrode surface, pseudocapacitors bridge the performance gap between electrostatic double-layer capacitors and batteries. In this context, molecular design offers the exciting possibility to create tunable and inexpensive organic electroactive materials. Here we describe a porous structure composed of perylene diimide and triptycene subunits and demonstrate its remarkable performance as a pseudocapacitor electrode material. The material exhibits capacitance values as high as 350 F/g at 0.2 A/g as well as excellent stability over 10 000 cycles. Moreover, we can alter the performance of the material, from battery-like (storing more charge at low rates) to capacitor-like (faster charge cycling), by modifying the structure of the pores via flow photocyclization. Organic materials capable of stable electron accepting pseudocapacitor behavior are rare and the capacitance values presented here are among the highest reported. More broadly, this work establishes molecular design and synthesis as a powerful approach for creating tunable energy storage materials.

High-performance transparent actuator made from Poly(dimethylsiloxane)/Ionic liquid gel

This paper presents the development of a new transparent actuator prepared from poly(dimethylsiloxane)/ionic liquid (PDMS/IL) gel electrolyte. The gel electrolyte film is prepared using a casting method and thin electrodes are applied by spray coating. Subsequently, the electrochemical and electromechanical properties of the PDMS/IL gel electrolyte actuator are investigated, which reveal its superior strain performance. The functioning mechanism of the actuator appears to originate from both the electrostatic double-layer capacitor (EDLC) and Faradaic capacitor (FC) mechanisms, with greater contribution of the former. These transparent, flexible, and robust films may have significant potential as actuator materials for wearable and transparent electronic and energy-conversion devices.

High-performance polymer actuators based on an iridium oxide and vapor-grown carbon nanofibers combining electrostatic double-layer and faradaic capacitor mechanisms

The electrochemical and electromechanical properties of polymer actuators that leverage the synergistic effect from combining a noble metal oxide (iridium oxide dihydrate (IrO2·2H2O)), vapor-grown carbon nanofibers (VGCFs) and an ionic liquid (IL) in the electrode were compared with those of actuators prepared using VGCFs or single-walled carbon nanotubes (SWCNTs) without IrO2, or with an IrO2·2H2O/carbon black (CB)/IL composition. The electrode in this actuator system is equivalent to an electrochemical capacitor, and exhibits behavior similar to that of both an electrostatic double-layer capacitor (EDLC) and a faradaic capacitor (FC). The mechanism underlying the functioning of the IrO2·2H2O/VGCF/IL actuators which exhibit from both EDLC and FC mechanisms was found to be different from that for devices produced using VGCFs or SWCNTs alone (which exhibit only the EDLC mechanism) and using IrO2·2H2O/CB/IL, which exhibit from both EDLC and FC mechanisms, with the FC mechanism providing the largest contribution. An IrO2·2H2O/VGCF/EMI[BF4] actuator exhibited a maximum strain of 0.75%, a value approximately 1.8 times that obtained from a SWCNT-only actuator. This device also generated a maximum blocking force stress of 2.58MPa (1.3 times that of a SWCNT-only actuator) and a maximum calculated stress of 0.66MPa (2.2 times that of a IrO2·2H2O/CB/EMI[BF4] actuator).Although the frequency dependence of the displacement responses of an IrO2·2H2O/CB/IL polymer actuator was not successfully simulated using a double-layer charging kinetic model in previous work, this was found to be possible for the IrO2·2H2O/VGCF/IL actuators in the present study. Simulations of the electromechanical response of the IrO2·2H2O/VGCF/IL actuators correctly predicted strains at low frequencies as well as the associated time constants, confirming that the model is applicable to both EDLC-based actuator systems and the newly fabricated EDLC/FC system. These results suggest that flexible, robust films enabled by the synergistic effect obtained by combining noble metal oxides and VGCFs can have significant potential as actuator materials for wearable and energy-conversion devices.

High-performance hybrid (electrostatic double-layer and faradaic capacitor-based) polymer actuators incorporating nickel oxide and vapor-grown carbon nanofibers.

The electrochemical and electromechanical properties of polymeric actuators prepared using nickel peroxide hydrate (NiO2·xH2O) or nickel peroxide anhydride (NiO2)/vapor-grown carbon nanofibers (VGCF)/ionic liquid (IL) electrodes were compared with actuators prepared using solely VGCFs or single-walled carbon nanotubes (SWCNTs) and an IL. The electrode in these actuator systems is equivalent to an electrochemical capacitor (EC) exhibiting both electrostatic double-layer capacitor (EDLC)- and faradaic capacitor (FC)-like behaviors. The capacitance of the metal oxide (NiO2·xH2O or NiO2)/VGCF/IL electrode is primarily attributable to the EDLC mechanism such that, at low frequencies, the strains exhibited by the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators primarily result from the FC mechanism. The VGCFs in the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators strengthen the EDLC mechanism and increase the electroconductivity of the devices. The mechanism underlying the functioning of the NiO2·xH2O/VGCF/IL actuator in which NiO2·xH2O/VGCF = 1.0 was found to be different from that of the devices produced using solely VGCFs or SWCNTs, which exhibited only the EDLC mechanism. In addition, it was found that both NiO2 and VGCFs are essential with regard to producing actuators that are capable of exhibiting strain levels greater than those of SWCNT-based polymer actuators and are thus suitable for practical applications. Furthermore, the frequency dependence of the displacement responses of the NiO2·xH2O/VGCF and NiO2/VGCF polymer actuators were successfully simulated using a double-layer charging kinetic model. This model, which accounted for the oxidization and reduction reactions of the metal oxide, can also be applied to SWCNT-based actuators. The results of electromechanical response simulations for the NiO2·xH2O/VGCF and NiO2/VGCF actuators predicted the strains at low frequencies as well as the time constants of the devices, confirming that the model is applicable not only to EDLC-based actuator systems but also to the fabricated EDLC/FC system.

Nanopatterning of Electrode Surfaces as a Potential Route to Improve the Energy Density of Electric Double-Layer Capacitors: Insight from Molecular Simulations.

Electrostatic double-layer capacitors (EDLCs) with room-temperature ionic liquids (RTILs) as electrolytes are among the most promising energy storage technologies. Utilizing atomistic molecular dynamics simulations, we demonstrate that the capacitance and energy density stored within the electric double layers (EDLs) formed at the electrode-RTIL electrolyte interface can be significantly improved by tuning the nanopatterning of the electrode surface. Significantly increased values and complex dependence of differential capacitance on applied potential were observed for surface patterns having dimensions similar to the ions' dimensions. Electrode surfaces patterned with rough edges promote ion separation in the EDL at lower potentials and therefore result in increased capacitance. The observed trends, which are not accounted for by the current basic EDL theories, provide a potentially new route for optimizing electrode structure for specific electrolytes.