Electrical Capacitance Research Articles

Improvement of fatigue endurance through modulating strain response in BaTiO3–Ca3Ti2O7 composite ceramics

Ferroelectric ceramics are highly desired for applications in energy storage devices due to their fast charge-discharge capability. However, electric field-driven gradual degradation of ferroelectric polarization (i.e., fatigue) inevitably results in a decrease in energy efficiency and energy storage density. Therefore, improving fatigue endurance is one challenge for their practical applications in energy storage devices. Here, we provide a strategy to modulate the strain response to the external electric field, and thus, increase the fatigue endurance by employing hybrid improper ferroelectricc Ca3Ti2O7 ceramic that exhibits a negative piezoelectric effect. We synthesized [Formula: see text] BaTiO[Formula: see text] Ca3Ti2O7 (BT-xCT) ceramics, in which the strain response of ceramics to the electric field gradually decreases with the increasing proportion of Ca3Ti2O7. For BT-0.3CT ceramic, the energy density storage efficiency is improved to 74.95% which is much higher than that of BT-0.1CT (48.07%). The strain response to the external electric field of BT-0.3CT is substantially lowered and almost reaches zero, leading to excellent fatigue endurance ability. This research work paves a route for designing ferroelectric ceramics with smaller strain response and enhanced fatigue endurance ability, which is expected to benefit a wide range of applications of ferroelectric ceramics in various electric capacitors and electric storage devices.

Peanut shell waste derived porous carbon for high-performance supercapacitors

Low-cost and high-performance porous carbon electrode materials are the key to supercapacitors. Here, we reported the preparation of porous carbon materials by high-temperature carbonization coupled with chemical activators (H3PO4, ZnCl2, KOH) using peanut shell waste. The as-synthesized porous carbon with KOH as the chemical activator (KOH-AC) has the best ideal electric double-layer capacitance performance, outperforming other activator-treated porous carbon. In the three-electrode system, the prepared KOH-AC electrode material showed an ultra-high specific capacitance of 575.7 F g−1 at a current density of 0.5 A g−1, good rate characteristics and excellent electrochemical stability (106.5 % initial capacitance after 10,000 cycles), which exceeded that of most biomass carbon-based materials. In the two-electrode system with 6 M KOH as electrolyte, the symmetrical supercapacitor based on KOH-AC showed a high specific capacitance of 390.9 F g−1 at 0.5 A g−1 current density in the voltage rang of 0–1.3 V, with the maximum energy density of 22.2 Wh kg−1 and power density of 319.97 W kg−1 and excellent cycle stability (93.8 % after 10,000 cycles). In addition, it is also studied that all-solid-state flexible symmetric supercapacitor in PVA/KOH electrolyte shows a high specific capacitance of 432.7 F g−1 at 0.5 A g−1 current density and can provide energy density of 18.2 Wh kg−1 and power density of 275.3 W kg−1. In summary, this work synthesized high-performance porous carbon materials from renewable and sustainable biological wastes, which provided a feasible method for the application of biomass carbon in energy storage.

Image reconstruction for ECT based on high-order approximate sensitivity matrix

Electrical capacitance tomography (ECT), widely used for industrial measurements, reflects the permittivity distribution of the imaging region by measuring capacitance. The image reconstruction method is a crucial factor in determining image quality. Normally, the ECT image is reconstructed by sensitivity matrix. To alleviate the effects of the soft field property of the traditional sensitivity matrix, we propose an ECT reconstruction method based on the high-order approximate sensitivity matrix. The high-order approximate sensitivity matrices with four different nonlinearities, including a traditional sensitivity matrix, are derived through electromagnetic field analysis. Both numerical simulation and experiment are implemented for four sensitivity matrices using the Tikhonov regularisation algorithm and Landweber algorithm. Sensitivity evaluation indicators, image evaluation metricises, and capacitance matching correlation coefficients are used to compare the performance of sensitivity matrices. The results show that the high-order approximate sensitivity matrix with suitable nonlinearities improves image reconstruction quality. In different flow regimes, the sensitivity matrix with proper linearity has obvious advantages for regimes with high nonlinearity. The high-order approximate sensitivity matrix leads to shorter calculation time and can be used by various algorithms to enhance image reconstruction quality.

Nitrogen and iron co-doped carbon quantum dots/MnO2 nanowire composites for flexible solid-state supercapacitors with high areal capacitance

Herein, the synthesis of MnO2 nanowires decorated with transition metal-doped carbon quantum dots (MCQDs) is described for use as binder-free flexible solid-state supercapacitors. In particular, the water-soluble Fe and N co-doped MCQDs prepared by amidation reaction with ferric ammonium citrate and urea had ultrafine particle morphologies and showed super-hydrophilicity in aqueous solution, which greatly improved the contact probability between the electrode and the electrolyte. In addition, the co-doped MCQDs increased both the electrical conductivity and specific capacitance of the MnO2/carbon-based nanocomposites and limited the collapse and exfoliation of the MnO2 structure during extended cycling. Compared with pristine MnO2 electrode, the MCQDs/MnO2 composite electrode exhibited faster charge-discharge rate and improved cycle stability with increased specific capacitance. The flexible symmetric supercapacitor constructed from the MCQDs/MnO2 composite had a capacitance retention of 85.6 % after 10,000 charge/discharge cycles at a current density of 2 mA cm−2. In addition, the device showed a maximum power density of 4.8 W cm−2 at an energy density of 2.3 mW h cm−2, and a maximum energy density of 11.16 mW h cm−2 at a power density of 311.6 mW cm−2. Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request.

Planar Array of Electrical Capacitance Tomography With Rotation

This paper investigates a rotational data collection strategy for planar array electrical capacitance tomography (ECT) to improve the imaging of complex-shaped objects in scenarios where access to the object is limited. Planar array of ECT can produce 2D and 3D images of changes in the dielectric permittivity of the object, but detecting complex-shaped objects may require more electrodes in the array, which can decrease the quality of capacitance measurements and make it challenging to detect objects at greater depths. With the air background as calibration measurements, by rotating the sensor array or the object, more independent data can be obtained, which can enhance image quality compared to traditional planar array ECT. The paper presents experimental results of image enhancement through visual reconstruction of known-shaped dielectric test samples and quantitative analysis against the ground truth. These findings suggest that rotational data collection has the potential to improve image quality in planar array ECT for detecting complex-shaped objects.

Low-frequency experimental method for measuring the electric double-layer capacitances of multi-cell electrolysis stacks based on equivalent circuit model

In recent years, the green hydrogen production via water electrolysis has acquired significant attention, and the dynamic operation of electrolysis stacks has become a crucial research area. The electric double-layer capacitance (EDLC) is the primary factor indicating the performance of the stack and affecting the dynamic behavior of the electrolysis stack. High-frequency testing methods are commonly used to measure the EDLCs of electrolysis cells in laboratory, but these methods are not suitable for cost-efficiency and a bottleneck of the engineering power electronic devices. This study proposes a novel square-wave pulse current (SPC) method for determining the EDLCs of multi-cell electrolysis stacks using industrial rectifiers. The response of the stack subjected to SPC is analyzed based on a semi-empirical equivalent circuit (SEEC) model. The feasibility of the proposed method is verified through experiments on a 2 Nm3/h alkaline water electrolysis stack, and an accuracy of 2.67% is obtained.

Localized Electron Density Regulation Effect for Promoting Solid-Liquid Ion Adsorption to Enhance Areal Capacitance of Micro-Supercapacitors.

The development of flexible microelectronic systems requires the construction of high-energy-output planar micro-supercapacitors (MSCs). Herein, the localized electron density, by introducing graphene quantum dots (GQDs) on the surface of electrodes, is regulated. The enhanced local field intensity promotes ion electrostatic adsorption at the solid-liquid interface, which significantly improves the energy density of MSCs in the confined space. Local electronic structure has been investigated from the perspective of the topological analysis of the electron localization function (ELF) and the electron density. Impressively, the edges of the simulated structure exhibit a higher electron density distribution than the CC skeleton. This finding indicates that the introduced GQDs reinforce the intrinsic electrical double-layer capacitance (EDLC) and the oxygen-bearing functional groups at the edge, further increasing the pseudocapacitance performance. Moreover, the edge electron aggregation effect enables the all-carbon-based symmetric MSCs to exhibit ultra-high areal capacitance (21.78mFcm-2 ) and excellent cycle stability (86.74% retention after 25000 cycles). This novel surface local charge regulation strategy is also applied for intensifying ion electrostatic adsorption on Zn-ion hybrid MSCs (polyvalent metal ions) and ion-gel electrolyte MSCs (non-metallic ions). With excellent planar integration, this device demonstrates excellent flexibility and has potential applications in timing and environmental monitoring.

High-energy-density flexible graphene-based supercapacitors enabled by atypical hydroquinone dimethyl ether

Supercapacitor is an electrochemical energy-storage technology that can meet the green and sustainable energy needs of the future. However, a low energy density was a bottleneck that limited its practical application. To overcome this, we developed a heterojunction system composed of two-dimensional (2D) graphene and hydroquinone dimethyl ether- an atypical redox-active aromatic ether. This heterojunction displayed a large specific capacitance (Cs) of 523 F g−1 at 1.0 A g−1, as well as good rate capability and cycling stability. When assembled in symmetric and asymmetric two-electrode configuration, respectively, supercapacitors can work in voltage windows of 0 ∼ 1.0 V and 0 ∼ 1.6 V, accordingly, and exhibited attractive capacitive characteristics. The best device can deliver an energy density of 32.4 Wh Kg−1 and a power density of 8000 W Kg−1, and suffered a small capacitance degradation. Additionally, the device showed low self-discharge and leakage current behaviors during long time. This strategy may inspire exploration of aromatic ether electrochemistry and pave a way to develop electrical double-layer capacitance (EDLC)/pseudocapacitance heterojunctions to boost the critical energy density.

Preparation of porous graphitic carbon and its dual-ion capacitance energy storage mechanism

A lithium-ion capacitor, a combination of a lithium-ion battery and a supercapacitor, is expected to have the advantages of both a battery and a capacitor and has attracted worldwide attention in recent years. However, its energy storage is limited due to the electric double-layer capacitance mechanism of the positive electrode. Consequently, to fundamentally improve the performance of the positive electrode material, a novel dual-ion hybrid capacitance energy storage mechanism is proposed. Porous graphitic carbon with a partially graphitized structure and hierarchical porous structure was synthesized by a one-step heat treatment method using potassium/magnesium/iron citrate as precursors. When used as the positive electrode material, the porous graphitic carbon has a dual-ion hybrid capacitance mechanism in an electrolyte produced using a mixture of Li-TFSI (bis(trifluoromethylsulfonyl) amine lithium salt) and BMIm-TFSI (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), which combines electric double-layer capacitance behavior in a lithium-ion capacitor and anion intercalation/de-intercalation behavior in a dual-ion battery. Two mechanisms were observed in the electrochemical characterization process, and the performance of the porous graphitic carbon was compared to porous carbon and artificial graphite, which indicate that its energy storage performance is significantly better due to the additional plateau capacity contributed by anion intercalation at a high potential and the improved conductivity through the local graphitic regions.

Impact of Faradaic Interlayer Confinement and Carbon-Centered Macrostructure Designs for Ion Capture and the Recovery of Elements.

Environmental protection associated with renewable energy is among the most critical challenges for translational ion-capture based on capacitive storage of ions in electrical double layers at the interface of electrode and electrolyte. Electric double-layer capacitance with charge induction and faradaic pseudo-capacitance with charge transfer classifies the capacitance of the electrochemical interface. The electrochemical interface in most energy technologies involves porous and pseudocapacitive redox materials that offer varying degrees of electrolyte confinement. In this review, we discuss the factors affecting water desalination, such as the effect of nanopores for ion capture, the ion sieving effect, the effect of hydration energy, and hydration radius in the carbon sub-nanometer pore. Moreover, the surface phenomena of electrodes, including carbon corrosion, and the potential of zero charge to control the oxidation of carbon electrodes are explained along with protection mechanisms. The various capacitive deionization (CDI) operations and the corresponding electrochemical cell technologies are briefly introduced, including the significance of double-layer charging materials with faradaic intercalation, which suffer less from co-ion expulsion. Finally, we revisit the effects of various nanoarchitectures and the construction of capacitive deionization electrodes for clean water technology.

Construction of Co9S8@NiCo2S4 core–shell hetero-nanostructure with synergistic effect of abundant mesopores and multi-metallic elements for novel high-performance flexible hybrid supercapacitors

Flexible portable supercapacitor devices have gained increasing attention in the field of energy storage in recent years. However, challenges remain in the selection of applicable flexible materials and/or the preparation of materials. Through our research, we have effectively constructed a flexible CS@NCS/CC core–shell hetero-nanostructured cathode material by anchoring Co9S8 (CS) nanopins on a flexible carbon cloth (CC) substrate firstly, and then wrapping NiCo2S4 (NCS) nanosheets on the outer surface of CS nanopins. In this process, we have improved the traditional two-step method of preparing NCS nanosheets into a one-step method, which has greatly improved the efficiency of the material preparation. The prepared CS@NCS/CC material has abundant mesopores, stable core–shell heterostructures and multiple valence states of metal ions, which enable the CS@NCS/CC electrode material to have strong electrochemical reaction kinetics and excellent cycling stability. Additionally, the CC as the flexible substrate improves the charge transfer capability of the transition metal composite. Benefiting from the synergistic effect of these favorable factors, the electrode material exhibits a high Cs value of 2020.6F g−1, which maintains 89.8% after 10,000 constant current charges and discharges. It is worth noting that the CS@NCS/CC can be folded and twisted at multiple angles, which proves that it can be used in wearable applications. The flexible hybrid supercapacitor CS@NCS/CC//AC/CC displays terrific energy density (58 Wh kg−1, at 800 W kg−1) with the synergistic effect of pseudocapacitance and electrical double-layer capacitance, and a capacitance retention rate of 92.9% after 10,000 cycles of constant current charging and discharging. Therefore, using CC as the flexible substrate and transition metal sulphides as the active material is an effective strategy for constructing high-performance flexible supercapacitors.

Novel favorably interconnected N-doped porous carbon hybrid electrode materials for high energy density supercapacitors

A strategy to prepare facile electrode materials for electrochemical capacitors with high conductivity, high surface area and hierarchical pore structure along with nitrogen functional groups to enhance the electrochemical performance, is presented in this work. Partially unravelled carbon nanotubes (PURNTs) are interconnected to the wrinkled few layered graphene nanosheets (WfG), which act as quick ion and charge transportation channels. Here, PURNTs acts as a spacer to the WfG to avoid the restacking. Though WfG-PURNTs exhibit good results, to further improve the electrochemical performance we developed an electrode material by designing nitrogen-doped porous carbon covered favorably interconnected WfG-PURNTs with interconnected pore structure. The WfG-PURNTs serve as the conductive matrix, which plays a key role in enhancing the N-PC (WfG-PURNTs) electrode material's electrochemical performance. And the nitrogen functional groups, through faradaic red-ox reactions, contribute to the pseudocapacitance in addition to the electric double layer capacitance, thereby enhancing overall supercapacitive performance. The developed N-PC (WfG-PURNTs)-700 shows a high nitrogen amount of 6.8 at %, with a high active surface area of 2418 m2 g−1. The synergistic effect of the WfG-PURNTs and N-doped porous carbon results in high supercapacitive performance and better cyclic stability. It shows an excellent specific capacitance (Cp) of 954 F g−1 at high current density of 2 A g−1. Also, the assembled symmetric supercapacitors show high energy densities of 61.1, 119.4, and 195.4 Wh kg−1 in acidic, neutral and ionic liquid electrolytes, respectively. We also designed asymmetric solid-state flexible supercapacitor which exhibits a high specific capacitance of 209.4 F g−1 at 2 A g−1 and an excellent energy density of 29.15 Wh kg−1. Furthermore, the assembled three such flexible supercapacitors in series connection, could able to light up red colored LED for 30 min once charged for 60 s.

Carbon Structures with Hollow Internal Cavity as Charge Storage Materials to Achieve High Energy Density

Hollow porous carbon spheres (HPCS) have been synthesized by using spherical silica nanoparticles (S–SiO2) as templates. S–SiO2 nanoparticles have been coated first with the polymer of phloroglucinol/1,4-phenylenediamine/formaldehyde (PPF), followed by a second layer of SiO2, and again with PPF as the third layer. After each step of coating, the sample has been pyrolyzed under nitrogen and S–SiO2 has been removed to obtain HPCS-I, HPCS-II, and HPCS-III, from the first, second, and third coated samples, respectively. The synthetic strategy relies on the use of a hard template to create void spherical cores and space confinement to develop shells of the hollow spheres. All of the materials show a uniform spherical morphology with a hollow inner core generated by the removal of the SiO2 template. The samples have been characterized by thermal analysis, powder X-ray diffraction, nitrogen adsorption/desorption studies, electron microscopy, and X-ray photoelectron spectroscopy. Among the samples, the structural formation of HPCS-II is found to be superior and it is also manifested in its electrochemical properties. While all of the samples exhibit near-rectangular cyclic voltammograms, the specific capacitance of HPCS-II is found to be the highest. Galvanostatic charge/discharge (GCD) studies also support the observation, and the specific capacitance is found to be 592 F·g–1 at a current density of 1 A·g–1, which is retained at 444 F·g–1 even at a very high current density of 100 A·g–1. The major contribution toward such electrochemical behavior is believed to arise from electrical double-layer capacitance (EDLC). HPCS-II is found to be highly stable, retaining 100% of its capacitance value at least up to 5000 GCD cycles. The power density of HPCS-II is nearly thrice the power target value projected by the Partnership for a New Generation of Vehicles (PNGV), and it shows an outstanding energy density value.

Study of Fluidization Behavior Transition from Geldart B to A Induced by High Temperature Using Electrical Capacitance Tomography

The transition of the fluidization behavior of Geldart B particles to that of A particles induced by temperature change was investigated by a developed high-temperature electrical capacitance tomography (ECT) sensor. Silica particles with a Sauter mean diameter of 237 μm and density of 2650 kg/m3, typically Geldart B particles under ambient conditions, were fluidized in a column of 5.5 cm from 20 to 600 °C. With the increase in temperature, ECT measurements showed a decrease in minimum bubbling velocity (Umb), no bed expansion characteristic in the homogeneous fluidization regime, an absence of multiple-bubbles regime, and a larger bubble size. The pressure drop against superficial gas velocity curves at elevated temperatures confirmed homogeneous fluidization between the minimum fluidization velocity (Umf) and Umb. Our analysis demonstrates that cohesive interparticle forces, which increase linearly with temperature, are responsible for the fluidization behavior transition of the silica particles.

Carbon Nanotube Field-Effect Transistor Biosensor with an Enlarged Gate Area for Ultra-Sensitive Detection of a Lung Cancer Biomarker.

Carcinoembryonic antigen (CEA) is a recognized biomarker for lung cancer and can be used for early detection. However, the clinical value of CEA is not fully realized due to the rigorous requirement for high-sensitivity and wide-range detection methods. Field-effect transistor (FET) biosensors, as one of the potentially powerful platforms, may detect CEA with a significantly higher sensitivity than conventional clinical testing equipment, while their sensitivity and detection range for CEA are far below the requirement for early detection. Here, we construct a floating gate FET biosensor to detect CEA based on a semiconducting carbon nanotube (CNT) film combined with an undulating yttrium oxide (Y2O3) dielectric layer as the biosensing interface. Utilizing an undulating biosensing interface, the proposed device showed a wider detection range and optimized sensitivity and detection limit, which benefited from an increase of probe-binding sites on the sensing interface and an increase of electric double-layer capacitance, respectively. The outcomes of analytical studies confirm that the undulating Y2O3 provided the desired biosensing surface for probe immobilization and performance optimization of a CNT-FET biosensor toward CEA including a wide detection range from 1 fg/mL to 1 ng/mL, good linearity, and high sensitivity of 72 ag/mL. More crucially, the sensing platform can function normally in the complicated environment of fetal bovine serum, indicating its great promise for early lung cancer screening.

Mechanochemical Pretreated Mn+1AXn (MAX) Phase to Synthesize 2D-Ti3C2Tx MXene Sheets for High-Performance Supercapacitors.

Two-dimensional (2D) MXenes sheet-like micro-structures have attracted attention as an effective electrochemical energy storage material due to their efficient electrolyte/cation interfacial charge transports inside the 2D sheets which results in ultrahigh rate capability and high volumetric capacitance. In this article, Ti3C2Tx MXene is prepared by a combination of ball milling and chemical etching from Ti3AlC2 powder. The effects of ball milling and etching duration on the physiochemical properties are also explored, as well as the electrochemical performance of as-prepared Ti3C2 MXene. The electrochemical performances of 6 h mechanochemically treated and 12 h chemically etched MXene (BM-12H) exhibit an electric double layer capacitance behavior with an enhanced specific capacitance of 146.3 F g-1 compared to 24 and 48 h treated samples. Moreover, 5000-cycle stability tested sample's (BM-12H) charge/discharge show increased specific capacitance due to the termination of the -OH group, intercalation of K+ ion and transformation to TiO2/Ti3C2 hybrid structure in a 3 M KOH electrolyte. Interestingly, a symmetric supercapacitor (SSC) device fabricated in a 1 M LiPF6 electrolyte in order to extend the voltage window up to 3 V shows a pseudocapacitance behavior due to Li on interaction/de-intercalation. In addition, the SSC shows an excellent energy and power density of 138.33 W h kg-1 and 1500 W kg-1, respectively. The ball milling pre-treated MXene exhibited an excellent performance and stability due to the increased interlayer distance between the MXene sheets and intercalation and deintercalation of Li+ ions.

An improved void fraction prediction model for gas-liquid two-phase flows in pipeline-riser systems

This paper introduces the application of void fraction prediction models (25 models total) from a simple horizontal pipe to a complex, real pipeline. The flow mechanism in the pipeline-riser system is explained based on the upstream phase interface and differential pressure in the downstream riser. The transition boundaries of “stratified to intermittent flow” and “stratified smooth to stratified wavy flow” in the horizontal section were predicted well by the models based on simple pipes. Electrical capacitance volume tomography was used to obtain the upstream void fraction just before the downstream gas-liquid eruption, α1, or during multiple cycles, α2. The difference between α1 and α2 are ranging between −10 % and 5 %. Finally, an improved correlation is proposed based on the model found to be best (Lockhart and Martinelli, with error values (root mean square error (RMSE) and mean absolute percentage error (MAPE)) of about 12 % and 18 %); the corresponding error levels (RMSE and MAPE) amount roughly to 5 % and 10 %, respectively. The improved model also delivers a good prediction for α1 when separating in two flow regimes. Overall, the finally proposed correlation reads and is found superior in terms of accuracy to all previously published correlations.

Anode Boundary Layer Extraction Strategy for H+–OH– Separation in Undivided Electrolytic Cell: Modeling, Electrochemical Analysis, and Water Softening Application

To promote the application of the electrolysis process for in situ pH adjustment of wastewaters with complex matrices, a robust, industrially scalable, and undivided electrolytic cell featuring the abstraction of H+ from the anode boundary layer was developed in this study, where a tubular Ti porous membrane was used as the anode. Modeling, electrochemical analysis, and COMSOL simulation results show that abstracting H+ from the anode boundary layer could effectively inhibit the transfer of H+ into the bulk solution with the decrease in the anode double-layer thickness and electric double-layer capacitance. Increasing the current density from 6 to 22 mA cm–2 and the influent rate from 330 to 11,100 mL min–1 deteriorated the H+–OH– separation performance, owing to the enhanced electro-migration of H+ into the bulk solution and turbulence state near the anode surface, respectively. The H+–OH– separation performance showed a volcanic type change trend with the acid extraction rate with the optimal value at 50 mL min–1, specifically the separation efficiency of 10%–72% and 16%–94% for H+ and OH– in the acidic and alkaline effluents, respectively, at an influent rate of 500 mL min–1 and a current density of 6–22 mA cm–2. Importantly, the present undivided electrolytic cell showed better H+–OH– separation performance than that of the widely studied membrane-based divided system. The feasibility of this undivided electrolytic cell was also validated by water softening experiments, where the Ca hardness removal efficiency was 42%–92% with energy consumption of 1.2–4.6 kWh (kgCaCO3)−1 at a current density of 6–22 mA cm–2. In general, this new undivided electrolytic cell opened a new pathway for in situ electrochemically regulating wastewater pH.

All-Solid-State Carbon Black Paste Electrodes Modified by Poly(3-octylthiophene-2,5-diyl) and Transition Metal Oxides for Determination of Nitrate Ions.

This paper presents new paste ion-selective electrodes for the determination of nitrate ions in soil. The pastes used in the construction of the electrodes are based on carbon black doped with transition metal oxides: ruthenium, iridium, and polymer-poly(3-octylthiophene-2,5-diyl). The proposed pastes were electrically characterized by chronopotentiometry and broadly characterized potentiometrically. The tests showed that the metal admixtures used increased the electric capacitance of the pastes to 470 μF for the ruthenium-doped paste. The polymer additive used positively affects the stability of the electrode response. All tested electrodes were characterized by a sensitivity close to that of the Nernst equation. In addition, the proposed electrodes have a measurement range of 10-5 to 10-1 M NO3- ions. They are impervious to light conditions and pH changes in the range of 2-10. The utility of the electrodes presented in this work was demonstrated during measurements directly in soil samples. The electrodes presented in this paper show satisfactory metrological parameters and can be successfully used for determinations in real samples.

Ethyl viologen-functionalized reduced graphene oxide composites for asymmetric ionic liquid-based supercapacitors

The development of pseudocapacitive materials matching ionic liquid (IL) electrolytes can significantly enhance the performance of supercapacitors (SCs). Herein we report an ethyl viologen-functionalized reduced graphene oxide composite (EV-RGO) synthesized by one-step hydrothermal method. In EV-RGO, the ethyl viologen cations are anchored on the RGO sheets through electrostatic interactions, π-π stacking interactions, and cation-π interactions, which makes EV-RGO as an electrode material more stable and reversible during charging and discharging. Meanwhile, the viologen cations with ethyl groups can better function as a spacer to suppress effectively the stacking of RGO sheets and expand their interlayer spacing. In 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) IL electrolyte, the electrochemical performance of the composite is enhanced due to synergic contributions from electric double-layer capacitance and pseudocapacitance. The pseudocapacitance mechanism is also supported by the results of XPS data. The specific capacitance of the EV-RGO as a negative electrode material for SCs reaches to 222.7 F g−1 at a current density of 0.5 A g−1. An asymmetric SC device (EV-RGO//AC ASC) exhibits an energy density of 64.1 Wh kg−1 at a power density of 888 W kg−1. This work offers an advanced strategy for the fabrication of high-performance SCs using organic molecule-modified graphene composites.