Interfacial Capacitance Research Articles

New method of measuring the permittivity of silicon wafer, with relevance to permittivity-based quality sensing

A new method of measuring the permittivity of silicon wafers is provided. It removes the previously reported dependence of the measured permittivity on the silicon resistivity and on the electrode quality. Metal-semiconductor contacts or thin-film electrodes are not required. The method innovatively uses N-segment (e.g., N = 7) sandwiching aluminum-foil electrodes adhered to both surfaces of the wafer using double-sided adhesive tape, which provides adhesion and resistance enhancement (for ensuring that the meter measures the capacitance correctly). By measuring the capacitance C for various values of the capacitor area A (as provided by different numbers of segments) and plotting 1/C vs. 1/A, the permittivity is obtained from the slope and the effect of the electrode-specimen interface capacitance is removed. The relative permittivity (12) equals the conventionally obtained values. By using a sufficiently high value of N, the permittivity spatial distribution can be probed, thus enabling spatially resolved permittivity-based quality sensing.

Construction of three‐dimensional crumpled Ni‐Co TMOs for electrochemical energy storage

AbstractDue to excellent electrochemical performances, mixed transition metal oxides (TMOs) as electrode materials have attracted scholarly attention. However, the issues of volume expansion, unstable structure, and low electrical conductivity have limited their development for lithium battery (LIB). Drawing on the strategy of MOFs derivation synthesis combined with low temperature hydrothermal method, this study successfully synthesized the three‐dimensional (3D) NiCo2O4@Fe2O3 with a flower‐like crossing channel and a surface crumpled structure. As anode for LIBs, NiCo2O4@Fe2O3 exhibits more reliable performance than Ni−Co oxides. Our experiments verified that the Ni−Co composite electrical conductivity and cycling stability were both improved by the Fe2O3 coating. Under the high current density of 1000 mA g−1, the capacity decay rate of NiCo2O4@Fe2O3 tends to be stable after 60 cycles, and the capacity remains at 945 mAh g−1 after 400 cycles. Besides, the specific crossing porous‐channel structure mode improved the composite's carrier transport efficiency, and coulombic efficiency reached 100 % after 400 cycles. Noteworthy is the fact that the crumpled surface structure formed by the 2D Ni−Co nanosheets promotes the construction of heterostructures, further enhances the interface capacitance effect, and strengthens the rating capacity.

Electrochemical contributions: John Edward Brough Randles (1912–1998)

John Edward Brough Randles (Figure 1) was an English electrochemist who made important contributions to the theoretical background of polarography, cyclic voltammetry, and electrochemical impedance spectroscopy. Many modern techniques of electrochemistry are descended from his work, including cyclic voltammetry, anodic stripping voltammetry, and various types of hydrodynamic voltammetry. The Randles-Ševčík equation applied on linear sweep voltammetry and cyclic voltammetry, and the Randles equivalent circuit used in the modeling of impedance spectra are named after him. The earliest electrochemical work of Randles performed with an oscillopolarograph (cathode ray polarograph) resulted in the development of linear sweep voltammetry.[1, 2] In addition to the experimental work, Randles solved a theoretical problem for expressing the current for diffusion-controlled electrochemical reactions by applying an ingenious graphical method.[3] Another important contribution of Randles to electrochemistry was in the theoretical analysis of Faraday impedance spectra published in 1947.[4] The Randles equivalent circuit has been applied to the analysis of the impedance spectra including interfacial electron transfer (Faradaic component), capacitance and diffusion contributions to the impedance. It became the most frequently used theoretical treatment of impedance spectra. It should be noted that similar results were obtained by Russian scientists Dolin and Erschler in 1940, but the papers published in the Russian language have not been seen by the electrochemical community. The Randles equivalent circuit (Figure 2) is one of the simplest and most common circuit models of electrochemical impedance. It includes a solution resistance, a double-layer capacitor, and a charge transfer or polarization resistance. While the Randles equivalent circuit is frequently sufficient for modeling simple electrochemical systems, it can be used as a starting point for more sophisticated models, for example, based on more resistances and capacitances organized in parallel or in a sequence. It should be noted that John Randles was not only working on solving theoretical problems in electrochemistry, but he was a very good experimentalist. As an example of his experimental work, the Volta potential difference between a mercury droplet and an electrolyte solution measured by Randles can be mentioned.[5] Notably, the great Russian electrochemist Alexander Frumkin had failed to obtain a stable and reproducible result for this kind of measurement. Randles published relatively few papers, but many of them are of great importance and his theoretical treatments of electrochemical systems have been included in all electrochemistry textbooks. The author declares that he has no conflict of interest.

Collectively exhaustive electrochemical hydrogen evolution reaction of polymorphic cobalt selenides derived from organic surfactants modified Co-MOFs

Finding and exploring non-noble metal-based electrocatalysts for the promising power-to-hydrogen fuel technology through water splitting reactions is highly emerging. Herein, we report the preparation of cobalt-based metal-organic frameworks (Co-MOFs) using an oleylamine (OLA) and 1-dodecanethiol (DDT)-modified trimesic acid (TMA), and cobalt precursor. Then, the electrocatalytically active cobalt selenides were derived from the Co-MOFs by a water-organic solvent mixture-assisted single-step selenization process. Interestingly, the cobalt selenide obtained from the DDT-modified Co-MOF shows collectively exhaustive hydrogen evolution reaction (HER) performance with very small overpotentials of ∼161 and ∼206 mV to achieve 10 and 50 mA cm−2, respectively, due to the phase mixing characteristics of cobalt selenide and the synergistic interaction. The fast reaction kinetics were identified at the DDT-Co selenide electrode surface as confirmed by observing the lower charge-transport/interfacial resistance and Tafel slope value due to the high surface coverage of adsorbed hydrogen (Hads) atoms, evidenced by high interfacial chemical capacitance value, as a result of the high electrical conductivity and large electrochemically accessible active sites. The calculated activation energy (Ea) of HER further reveals a low kinetic energy barrier in the HER on the DDT-Co selenide, indicating high intrinsic catalytic activity due to the fast surface diffusion rate of Hads. Furthermore, the obtained cathodic transfer coefficient (αc) value strongly suggested that the HER on the surface of DDT-Co selenide (αc = 2) proceeds in the Langmuir-Hinshelwood reaction mechanism and follows the Volmer-Tafel pathway. The present work provides valuable insights into the modification of Co-MOFs and their impact on HER catalytic activity of cobalt selenide, and also the mechanistic investigation of HER based on electrochemical impedance spectroscopy analysis.

Exploring the linear relationship between potential dynamics and interfacial capacitance: implications for enhancing the turnover frequency in electrochemical water splitting

Effect of scan rate over intrinsic activity or TOF for OER, has been analysed for the very first time. It has found that increased TOF value varies as a function of scan rate which arises due to increased interfacial capacitance.

Electric Double Layer Structure in Electrocatalytic Carbon Dioxide Reduction

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.

RGO-PANI composite Au microelectrodes for sensitive ECIS analysis of human gastric (MKN-1) cancer cells

Microelectrode-based cell chip studies for cellular responses often require improved adhesion and growth conditions for efficient cellular diagnosis and high throughput screening in drug discovery. Cell-chip studies are often performed on gold electrodes due to their biocompatibility, and stability, but the electrode–electrolyte interfacial capacitance is the main drawback to the overall sensitivity of the detection system. Thus, here, we developed reduced graphene oxide-polyaniline-modified gold microelectrodes for real-time impedance-based monitoring of human gastric adenocarcinoma cancer (MKN-1) cells. The impedance characterization on modified electrodes showed 28-fold enhanced conductivity than the bare electrodes, and the spectra were modeled with proper equivalent circuits to extrapolate the values of circuit elements. The impedance of both time-and frequency-dependent measurements of cell-covered modified electrodes with equivalent model circuits was analyzed to achieve cellular behavior, such as adhesion, spreading, proliferation, and influence of anti-cancer agents. The normalized impedance at 41.5 kHz (|Z|norm 41 kHz) was selected to monitor the cell growth analysis, which was found linear with the proliferation of adherent cells along with the influence of the anticancer drug agent on the MKN-1 cells. The synergistic effects and biocompatible nature of PANI-RGO modifications improved the overall sensitivity for the cell-growth studies of MKN-1 cells.

On the use of a constant phase element (CPE) in electrochemistry

Several techniques can be used to experimentally determine the interfacial capacitance of an electrode, which is a crucial parameter used for quantifying the efficiency of supercapacitors. However, the values obtained from cyclic voltammetry can be significantly different from those extracted from electrochemical impedance spectroscopy analysis. This is particularly due to the fact that the interface does not behave like an ideal (i.e., frequency independent) capacitor, and requires the adoption of a constant phase element (CPE). In this article, we present the state of the art on this apparent difference and on the error that can result from one or the other technique using CPE analysis.

Taming Electrowetting Using Highly Concentrated Aqueous Solutions.

Wetting of carbon surfaces is one of the most widespread, yet poorly understood, physical phenomena. Control over wetting properties underpins the operation of aqueous energy-storage devices and carbon-based filtration systems. Electrowetting, the variation in the contact angle with an applied potential, is the most straightforward way of introducing control over wetting. Here, we study electrowetting directly on graphitic surfaces with the use of aqueous electrolytes to show that reversible control of wetting can be achieved and quantitatively understood using models of the interfacial capacitance. We manifest that the use of highly concentrated aqueous electrolytes induces a fully symmetric and reversible wetting behavior without degradation of the substrate within the unprecedented potential window of 2.8 V. We demonstrate where the classical "Young-Lippmann" models apply, and break down, and discuss reasons for the latter, establishing relations among the applied bias, the electrolyte concentration, and the resultant contact angle. The approach is extended to electrowetting at the liquid|liquid interface, where a concentrated aqueous electrolyte drives reversibly the electrowetting response of an insulating organic phase with a significantly decreased potential threshold. In summary, this study highlights the beneficial effect of highly concentrated aqueous electrolytes on the electrowettability of carbon surfaces, being directly related to the performance of carbon-based aqueous energy-storage systems and electronic and microfluidic devices.

Design and testing of a capacitive interface for underwater stretch sensors

The growing popularity of wearable electronics has seen substantial research in soft and flexible strain sensors. From athletic performance analysis to human augmentation, there is a wide range of applications being developed. An area often overlooked is the connections between a network of wearable sensors and their measurement electronics. In dry applications this is as simple as cabling between the two. In underwater environments however this becomes more complicated. Capacitive strain sensors have been used to demonstrate underwater sensor-based motion capture in both a robotic fish and smart glove for divers. Wired connections introduced failure points and eliminated the modularity of the system for potted electronics. In this paper we have demonstrated the use of a capacitive interface as a wireless method to connect wearable strain sensors across an encapsulation to electronics. This removes the need to have wires permanently protruding through the encapsulation. The interfaces’ impact on strain sensor sensitivity and measurement method has been investigated for both resistive and capacitive-based strain sensing.

Ultra-Thin SnOx Buffer Layer Enables High-Efficiency Quantum Junction Photovoltaics.

Solution-processed solar cells are promising for the cost-effective, high-throughput production of photovoltaic devices. Colloidal quantum dots (CQDs) are attractive candidate materials for efficient, solution-processed solar cells, potentially realizing the broad-spectrum light utilization and multi-exciton generation effect for the future efficiency breakthrough of solar cells. The emerging quantum junction solar cells (QJSCs), constructed by n- and p-type CQDs only, open novel avenue for all-quantum-dot photovoltaics with a simplified device configuration and convenient processing technology. However, the development of high-efficiency QJSCs still faces the challenge of back carrier diffusion induced by the huge carrier density drop at the interface of CQDs and conductive glass substrate. Herein, an ultra-thin atomic layer deposited tin oxide (SnOx ) layer is employed to buffer this carrier density drop, significantly reducing the interfacial recombination and capacitance caused by the back carrier diffusion. The SnOx -modified QJSC achieves a record-high efficiency of 11.55% and a suppressed hysteresis factor of 0.04 in contrast with reference QJSC with an efficiency of 10.4% and hysteresis factor of 0.48. This work clarifies the critical effect of interfacial issues on the carrier recombination and hysteresis of QJSCs, and provides an effective pathway to design high-performance all-quantum-dot devices.

Capacitive energy storage from single pore to porous electrode identified by frequency response analysis

Rate capability, peak power, and energy density are of vital importance for the capacitive energy storage (CES) of electrochemical energy devices. The frequency response analysis (FRA) is regarded as an efficient tool in studying the CES. In the present work, a bi-scale impedance transmission line model (TLM) is firstly developed for a single pore to a porous electrode. Not only the TLM of the single pore is re-parameterized but also the particle packing compactness is defined in the bi-scale. Subsequently, the CES properties are identified by FRA, focused on rate capability vs. characteristic frequency, peak power vs. equivalent series resistance, and energy density vs. low frequency limiting capacitance for a single pore to a porous electrode. Based on these relationships, the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length, intra-particle pore diameter, inter-particle pore diameter, electrolyte conductivity, interfacial capacitance & exponent factor, electrode thickness, electrode apparent surface area, and particle packing compactness. Finally, the experimental diagnosis of four supercapacitors (SCs) with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore. The calculating results suggest, to some extent, the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode. Hence, in order to design a better porous electrode, more attention should be given to the inter-particle pore.

Theoretical understanding of electrocatalysis beyond thermodynamic analysis

As the green and sustainable development of human society highly relies on renewable energy, it has been recognized that electrocatalysis is a key technology to this end. High efficient ways of carbon-neutralization (eCO2RR), reverse artificial nitrogen cycle (RANC), and oxygen chemistry (OER and ORR) all can be driven by electrocatalysis. Advanced theoretical study is an important means to fundamentally understanding electrocatalytic reactions. Herein, we review a few significant issues in theoretical electrocatalysis. First, electrochemical barriers and potential effects are essential for a more accurate description of reaction mechanism and activity. Meanwhile, consideration of competitive reaction path is also one of the important aspects, as novel insights and anomalous volcano trend can be obtained. Finally, a microenvironment exerted by confined space can tune the capacitance of electrochemical interface and (electro)chemical potential of proton, resulting in a possibility to improve reaction activity, which opens a new avenue for design of catalyst.

Electrochemical Characterization of the Self-Assembled 4,4’-Bipyridine Layers at the Electrode | Ionic Liquid Interface

Self-assembled monolayers (SAMs) have significant importance in many modern applications1-2. The properties of SAMs depend on many aspects, such as the characteristics of individual molecules, forming the monolayer; by the interactions between these molecules; and SAM interactions with the electrolyte; the crystalline surface of the substrate; etc3. Therefore, the fundamental studies of these systems are crucial in determining the function of SAMs in various applications4-5.The aim of the current work was to study the adsorption characteristics of 4,4’- bipyridine from ionic liquid media at different electrodes6.Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted to characterize the electrochemical behavior of the self-assembled 4,4’-bipyridine (4,4’-BP) layers at the Sb(111) and Cd(0001) | 4,4’-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface. All the experiments were carried out in a three-electrode electrochemical cell in a glove-box, i.e., a nitrogen-controlled atmosphere.CV method was used to examine the electrochemical characteristics of the system under investigation within the potential region −0.9 V < E < 0.0 V for Sb(111) and −2.1 V < E < -0.8 V for Cd(0001) vs. Ag|AgCl. The current values increase rapidly at the more negative end of the studied potential region, indicating that reduction processes started at the Sb(111) and Cd(0001) | 4,4’-BP+EMImBF4 interface. In contrast with the data measured in EMImBF4, where the system shows ideal polarisable behaviour in the whole potential range. Interfacial capacitance (C s) values were calculated using the relation Cs=−(Z′′2\U0001d70bf)−1 . Capacitance values calculated depend on the composition of the electrolyte (i.e., on the concentration of 4,4’-BP), electrode material as well as on applied potential. Cs values are lower in the mixture than those measured in pure EMMImBF4 at a certain potential region in the case of both electrode materials. This effect is caused by the adsorption of 4,4’-BP molecules at the electrode surface. The shape of the phase angle vs. frequency (f) curves shows that mixed kinetic processes occur in the whole f range measured (i.e. diffusion and charge transfer steps in addition to adsorption).Acknowledgments:This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

(Invited) Dielectric Screening of Ionic Liquids and Implications for Their Capacitance, Solvation, and Structural Properties

Development and utilization of ionic liquids for applications as electrolytes and solvents requires understanding their electrostatic interactions with solutes, co-solvents, and interfaces. In this regard, the bulk dielectric constant of an ionic liquid is of little use, but rather the dielectric response must be characterized at atomistic lengthscales. We will discuss the dielectric response of ionic liquids as computed from molecular dynamics simulations and statistical mechanical theory. We will then describe how the dielectric properties of ionic liquids are connected with observed trends in interfacial capacitance, solvation, and liquid structure. Comparisons will be made to aqueous electrolytes and molten salts, and similarities and differences will be discussed.

Carbon-Based Transducers for Solid-Contact Calcium Ion-Selective Electrodes: Mesopore and Nitrogen-Doping Effects.

Solid-contact ion-selective electrodes (SC-ISEs) exhibit great potential in the detection of routine and portable ions which rely on solid-contact (SC) materials for the transduction of ions to electron signals. Carbon-based materials are state-of-the-art SC transducers due to their high electrical double-layer (EDL) capacitance and hydrophobicity. However, researchers have long searched for ways to enhance the interfacial capacitance in order to improve the potential stability. Herein, three representative carbon-based SC materials including nitrogen-doped mesoporous carbon (NMC), reduced graphene oxide (RGO), and carbon nanotubes (CNT) were compared. The results disclose that the NMC has the highest EDL capacitance owing to its mesopore structure and N-doping while maintaining high hydrophobicity so that no obvious water-layer effect was observed. The Ca2+-SC-ISEs based on the SC of NMC exhibited high potential stability compared with RGO and CNT. This work offers a guideline for the development of carbon-material-based SC-ISEs through mesoporous and N-doping engineering to improve the interfacial capacitance. The developed NMC-based solid-contact Ca2+-SC-ISE exhibited a Nernstian slope of 26.3 ± 3.1 mV dec−1 ranging from 10 μM to 0.1 M with a detection limit of 3.2 μM. Finally, a practical application using NMC-based SC-ISEs was demonstrated through Ca2+ ion analysis in mineral water and soil leaching solutions.

Molecularly Imprinted Polymer Modified with an MWCNT Nanocomposite for the Fabrication of a Barbital Solid-Contact Ion-Selective Electrode.

For potentiometric sensing of barbital (BAR), unique micro-sized imprinted polymer/multiwalled carbon nanotube (MWCNT)-based sensors are introduced. MWCNT is a lipophilic ion-to-electron transducing substance. A synthetic, described, and integrated barbital sodium molecular imprinted polymer (MIP) was used as a recognition receptor for potentiometric transduction in a plasticized polyvinyl chloride membrane. Methacrylic acid and ethylene glycol dimethacrylic acid are used as the functional monomer and crosslinking agent, respectively, in the synthesis of the MIPs. In the operating concentration range of 1.0 × 10–3 to 2.0 × 10–7 M, the sensors’ Nernstian slope was −56.8 ± 0.9 mV/decade, with a detection limit of 1.0 × 10–7 M. The sensor displayed an accurate response time of 10 s and consistent potential response in the pH range of 8.5–11. Using chronopotentiometry tests, the interfacial capacitance of the presented ion-to-electron transducer was assessed. When compared to sensors without MWCNTs, the interfacial double-layer capacitance for sensors based on those layers reached 52.5 μF. After the addition of the MWCNTs nanocomposite layer, the water layer was eliminated between the sensing membrane and the conducting substrate. A wide range of applications for the proposed sensors for BAR detection in real samples can be provided by the sensors’ strong selectivity over the interfering species. The suggested sensors were successfully used to determine BAR in urine samples that had been spiked.

All-solid-state paper-based potentiometric combined sensor modified with reduced graphene oxide (rGO) and molecularly imprinted polymer for monitoring losartan drug in pharmaceuticals and biological samples

A cost-effective, highly selective and sensitive paper-based potentiometric combined sensor for losartan potassium drug (LOS) is fabricated, characterized and used for the drug monitoring. The sensor consists of 2 strips of filter paper (20 × 5 mm each) as platform, each imprinted with 4 mm diameter circular spot of carbon. One carbon spot is covered by a reduced graphene oxide (rGO) for use as a substrate for the recognition sensor and the other without rGO is used for the reference electrode. LOS molecularly imprinted drug polymer (MIP) is applied onto the graphene oxide containing strip to act as a drug recognition sensing material and a solid-state polyvinyl butyral (PVB) is applied onto the second carbon spot to act as a reference electrode. Performance characteristics of the combined sensor are examined with chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Increase effect of rGO on the interfacial double-layer capacitance of the sensing membrane and consequently on the potential stability is confirmed. The developed combined sensor (strip cell) displays a Nernstian slope of −58.2 ± 0.3 mV/decade (R2 = 0.9994) over the linear range 8.5 × 10−7 - 6.9 × 10−2 M with a detection limit of 2.7 ± 0.3 × 10−7 M. The sensor shows remarkable selectivity toward various related compounds especially those commonly used by the COVID-19 patients such as paracetamol, ascorbic acid and dextromethorphan. The assay method is validated and proved to be satisfactory for direct potentiometric determination of LOS-K in some pharmaceutical formulations and in spiked human urine samples. An average recovery of 96.3 ± 0.3–98.7 ± 0.6% of the nominal or spiked concentration and a mean relative standard deviation of ±0.6% are obtained. The use of an indicating and a reference electrodes combined into a single flexible disposable paper platform enables applications to a minimum sample volume due to the close proximity of the responsive membrane and the liquid junction. The efficiency of the proposed sensor in complex urine matrix suggests its application in hospitals for rapid diagnosis of overdose patients and for quality control/quality assurance tests in pharmaceutical industry.

Theoretical and experimental investigation of electrical double layer capacitance of LiClO4-interacted metal substrates and carbon-coated nickel electrode

ABSTRACT Suitable transitional metal electrode substrate should keep high electroactivity and meanwhile suppress polarization effect. Theoretical calculation and experimental measurement are adopted to investigate interfacial interaction-dependent capacitance of lithium perchlorate-titanium and nickel (LiClO4-Ti, LiClO4-Ni) metal substrates. LiClO4-Ti reveals ideal electrical double layer capacitance due to electrochemical stability and LiClO4-Ni reveals the deviated electrical double layer capacitance due to polarization effect in potential range of 0–0.8 V. LiClO4-Ni reveals lower ohmic resistance, charge transfer resistance and Warburg resistance to present higher conductivity, more active interface, and more feasible ion diffusion properties than LiClO4-Ti. Titanium and nickel substrates achieve mean response current of 0.13–2.47 μA cm−2 and 1.03–22.20 μA cm−2 at 5200 mV s−1. The corresponding specific capacitances are 0.010–0.0095 mF cm−2 and 0.322–0.155 mF cm−2 at 0.01–0.10 mA cm−2. LiClO4-Ni keeps much higher capacitance but relatively lower electrochemical stability than LiClO4-Ti. Theoretical calculation proves interfacial electrostatic adsorption of LiClO4 on Ti and Ni substrates could change charge density distribution. LiClO4-Ni with the enlarged potential difference causes intensified polarization effect. LiClO4-Ni exhibits higher electrical conductivity and lower interface energy than LiClO4-Ti. Furthermore, carbon-coated nickel (C@Ni) was prepared to mostly restrain polarization effect and meanwhile keep high electroactivity of Ni substrate for the promising supercapacitor electrode application. It reveals specific capacitance of 25.9 mF cm−2 and cycling capacitance retention of 94.5% after 1000 charge-discharge cycles at 1.0 mA cm−2 in 1.0 M LiClO4. The C@Ni electrode accordingly exhibits superior electroactivity and electrical double layer capacitance for energy storage application.

Effect of vacancy defects and co-doping on the quantum capacitance of silicene-based electrode materials

The design of electrode materials with high energy storage properties plays a key role in developing electric double-layer supercapacitor technology. In recent years, silicene has aroused great interest in the field of energy storage. In this paper, the electronic structure and quantum capacitance of single vacancy defects, topological defects and four kinds of double vacancy defects were systematically investigated, based on density functional theory. It is found that silicene with the topological defect is the most stable defect structure, with the formation energy of 2.067 eV. In the systems of Ag, Au, Cu, Ti, Mn and N co-doping on silicene, the structural stability enhances with the increase of N atoms. CuN2-o-Si structure shows the highest quantum capacitance of 145.499 μF/cm2, which could be an ideal anode material for supercapacitors. The increased quantum capacitance is due to the introduction of localized states near the Fermi level. Both defects and doping can enhance the quantum capacitance of silicene-based electrode materials, and then improve the total interfacial capacitance.