Specific Electrical Conductivity Research Articles

Collaboratively intercalated 1D/3D carbon nanoarchitectures in rGO-based aerogel for supercapacitor electrodes with superior capacitance retention

Reduced graphene oxide (rGO)-based aerogels with multidimensional structures have shown enormous potential for electrodes in supercapacitors. Currently, the interlayer stacking of rGO largely limits their capacitance performance and leads to poor structural stability. Herein, the multidimensional all-carbon aerogel of helical carbon nanocoils (CNCs)/rGO/carbon nanofibers (CNFs) has been synthesized by hydrothermal self-assembly and in-situ chemical vapor deposition (CVD). In this ternary electrode, three-dimensional (3D) CNCs serve as the inner skeleton, which facilitates the construction of 3D porous architectures and reinforces the structural stability. The intercalated CNCs prevents the stacking of rGO and effectively enlarges the spaces between rGO. Moreover, the uniform growth of one-dimensional CNFs improves the specific surface area and electrical conductivity. Due to the synergistic effect and hierarchical assembly of these components, the CNCs/rGO/CNFs electrode not only exhibits a high areal capacitance of 1581.7 mF cm−2 at 0.5 mA cm−2 in a 6 M KOH electrolyte but also shows excellent cycling durability with 108.1% capacitance retention over 30,000 cycles. This work provides inspiration and guidance for the design of multidimensional electrode materials, which has huge application potential in future energy storage devices.

Features of a burning electric arc superimposed on gas discharge with liquid electrolyte cathode

The conditions for burning an electric arc in a discharge plasma with a solution cathode have been studied. Both discharges were connected to the same metal anode. The electric arc burned in the current range of 5–10 A. The discharge current with a solution cathode varied within 8-15 A. In the experiments, aqueous solutions of common salt were used. The specific electrical conductivity of the solutions was 10–15 mS/cm. Spectral investigations of arc plasma radiation and discharge with a solution cathode have been carried out. Calculations of the parameters of the electron gas in the plasma column have been performed.

Low-current arc in plasma flow from discharge with liquid electrolyte cathode

The effect of plasma flow from a discharge with a solution cathode on the properties of a low-current electric arc has been experimentally studied. Electric power was supplied to the arc from a GORN-type inverter source. A rectifier served as a power source for the discharge with a solution cathode. The output voltage was 1700 V. Aqueous solutions of table salt were used in the experiments. The specific electrical conductivity of the solutions was in the range of 10–15 mS/cm. The electric arc was ignited between horizontally oriented rod electrodes. The interelectrode distance varied within 2–15 mm. The discharge current with a water cathode was established within 8–15 A. The arc burned in the current range of 1–8 A. The conditions under which stable burning of the electric arc is ensured are revealed.

Creation of plasma flow from a liquid electrolyte cathode with an arbitrary orientation in space

The gas discharge between a metal electrode and a liquid electrolyte supplied through a porous refractory material has been experimentally studied. The studies were carried out in the current range of 5–15 A. Aqueous solutions of sodium chloride were used as a liquid electrolyte. The specific electrical conductivity of the solutions was in the range of 6–18 mS/cm. The conditions necessary for the formation of a plasma flow are revealed. Plasma flows oriented in different directions in space have been created. The energy and spectral properties of the gas discharge are investigated.

Coherent Structures at the Interface between Water Masses of Confluent Rivers

The paper presents the results of field measurements and numerical modeling of the influence of various factors on the formation of coherent structures in the confluence zone of the Sylva and Chusovaya rivers, which are dammed by the Kamskaya Hydroelectric Power Station (HPS). A characteristic feature of the measured parameters in the zone under study is that they experience both seasonal fluctuations and fluctuations of much higher frequency associated with intraday regulation of the HPS operation. These intraday fluctuations give rise to coherent structures with periodicity T~2–10 min, which manifest themselves in the fluctuations of the specific electrical conductivity of water. The flow velocity also experiences significant fluctuations with a sufficiently wide frequency spectrum, although the characteristic period of its fluctuations is less than the period of electrical conductivity fluctuations and is equal to ~1 min. In order to study the features of the formation of such structures, numerical simulation was carried out within the framework of the three-dimensional approach. Calculations were performed for a 300-meter-long stretch of the Chusovaya River, which is located downstream of the confluence of Chusovaya and Sylva rivers and is the site of the Chusovskoy water intake of Perm city. It was found that the intraday irregularity of HPS operation gives rise to the occurrence of vortex structures in this layer, leading to the temporal variation of concentration at a given point of space and the formation of the wave structure of the concentration field at different moments of time. Time period and spatial scale of such vortex structures depend on the ratio of velocities of water masses and difference in their mineralization and, accordingly, in densities. Moreover, the period of fluctuations is proportional to the ratio of flow velocities. These estimations are of fundamental importance for the implementation of stable selective intake of water with required consumer properties under conditions of intraday irregularity of hydroelectric power station operation.

Ag doped Co/Ni bimetallic organic framework for determination of luteolin

Electrochemical determination of luteolin is vital to food industry owing to its bioactive properties such as anti-viral, anti-ulcer. However, bare electrode of traditional electrochemical sensors generally have narrow linear range and low sensitivity, which sets limit on their practical application. Accordingly, a new nano-architecture fabricated with Ag doped CoNi-bimetal metal–organic frameworks (Ag-CoNi-MOF) is developed as a material for electrochemical determination of luteolin. The introduction of Ag to three-dimensional (3D) flower-like hierarchical structure greatly increases specific surface area and electrical conductivity, which subsequently provides more excellent active sites for luteolin oxidation. Under optimal conditions, Ag-CoNi-MOF sensor presents a broader linear response to luteolin concentration of 0.002 – 1.0 μM with the detection limit as low as 0.4 nM (S/N = 3). Ag-CoNi-MOF has good anti-interference according to compared amperometric current response of luteolin within different organic analytes and metal ions. Finally, the sensor platform is implemented directly to determine luteolin in human urine for evaluation of its practical application. In general, Ag-CoNi-MOF sensors fabricated perform larger linear range with high sensitivity and anti-interference properties, which can be used as a potential material for electrochemical determination of luteolin.

Synchronous electrochemical detection of dopamine and uric acid by a PMo12@MIL-100(Fe)@PVP nanocomposite

In this work, a noble-metal-free composite electrode was prepared based on PMo12O403− (PMo12), C9H5FeO7 (MIL-100(Fe), a Fe-based metal organic framework) and polyvinylpyrrolidone (PVP), and served as a high performance electrochemical sensor for synchronous detection of dopamine (DA) and uric acid (UA). The PMo12@MIL-100(Fe)@PVP composite electrode was fabricated by a in-situ hydrothermal method. Thanks to the synergistic effect of three active components (PMo12, MIL-100 and PVP), the electrode possesses large specific surface area and high electrical conductivity and therefore it shows high electrocatalytic oxidation performance of DA and UA with a spacing of 0.146 V between the two peak positions. These benefits of the electrode enable its electrochemical sensor to synchronously detect of DA and UA. Namely, the linear ranges can achieve 1–247 μM for DA and 5–406 μM for UA. Meanwhile, the detection limits are 0.586 μM for DA and 0.372 μM for UA. Moreover, the sensor can be applied to simultaneous determination of UA and DA in human serums with satisfactory recovery values.

High performance supercapacitors assembled with hierarchical porous carbonized wood electrode prepared through self-activation

Carbonized wood (CW) electrodes with low-tortuosity and high conductivity have received extensive attention in the fields of energy storage and electrocatalysis. Directly carbonized wood electrodes have low specific surface area and high electrochemical impedance, and require secondary physical or chemical activation to achieve acceptable performance. Herein, we reported a facile method to prepare the CW electrode with superior surface area through self-activation using CO2 and water vapor generated during the pyrolysis which was conducted with a low inert gas flow rate. The specific surface area and electrical conductivity of the self-activated carbonized wood (SCW, ~ 0.46 g cm−3) were as high as 1145 m2 g−1 and 20.3 S cm−1, respectively. The SCW applied as a freestanding electrode demonstrated an impressive specific capacitance of 6.63 F cm−2 (143.6 F g−1) at 1 mA cm−2. After 10,000 cycles, the capacitance of the SCW electrode was retained as high as 101.7%. The symmetrical supercapacitor (SSC) assembled with two SCW electrodes showed an energy density of 0.27 mWh cm−2 (8.60 Wh L−1) at a power density of 0.5 mW cm−2 (11.8 W L−1). This work provides a simple, low-cost and green procedure for fabricating high-performance CW electrodes, which has great promotional significance and practical value on valorization of biomass.

Ginsenoside Rg3 determination using an electro-synthesized molecularly imprinted polymer on MWCNT-Ti3C2Tx nanocomposite modified electrode

Rare ginsenoside Rg3 is a main active ingredient in ginseng, which is more easily absorbed by human body and plays its role. Determination of Rg3 in edible and medicinal samples is a key factor for quality evaluation and effective monitoring of adulteration. In this study, an electrochemical sensor was developed based on molecularly imprinted polymer (MIP) and nanomaterial amplification. MIP was achieved by electro-polymerization with Rg3 as the template molecule and the functional monomer was o-phenylenediamine. Multi-walled carbon nanotubes (MWCNT) and titanium carbide (Ti3C2Tx) nanocomposites formed an excellent porous structure, which exhibited the advantages of increasing the specific surface area and electrical conductivity. The prepared sensor presented a great linear relation of Rg3 in the range of 10–2000 μg mL−1 with a limit of detection (LOD) of 0.34 μg mL−1. Importantly, the sensor was successfully utilized to detect ginsenoside Rg3 in different real samples.

Structure-activity relationship of carbon additives in cathodes for advanced capacitor batteries

Capacitive lithium-ion batteries with a dual-energy storage mechanism can provide a high energy and power density, which are constructed by the addition of slightly porous carbon. Here, the effect from porous carbon, such as the proportion, specific surface area, pore size and electrical conductivity, on the rate performance is systematically studied using hybrid electrodes with LiNi0.6Co0.2Mn0.2O2 and activated carbon or carbon aerogel. Compared with LiNi0.6Co0.2Mn0.2O2 electrodes, the hybrid electrodes demonstrate a lower resistivity, smaller electrochemical polarization, stronger rate capability and stable capacity retention. Furthermore, Adding carbon aerogel into LiNi0.6Co0.2Mn0.2O2 material is more conducive to enhancing the rate performance when compared with activated carbon. The lithium-ion full capacitor battery configured of a hard carbon anode and LiNi0.6Co0.2Mn0.2O2-carbon aerogel delivers a capacity of 97.3 mAhg−1 at 10C with an energy density reaching 323.8 Wh∙kg−1 (vs. the cathode), showing bright prospects in energy storage system with both high specific energy and power densities.

Effect of a Metallocene Catalyst Mixture on CNT Yield Using the FC-CVD Process

This work studies synthesis of carbon nanotube (CNT) sheet using the high temperature (1400 °C) floating catalyst chemical vapor deposition (FC-CVD) method. Three metallocenes—ferrocene, nickelocene, cobaltocene—and their combinations are used as precursors for metal catalysts in the synthesis process. For the carbon source, an alcohol fuel, a combination of methanol and n-hexane (9:1), is used. First, the metallocenes were dissolved in the alcohol fuel. Then, the fuel mixture was injected into a tube furnace using an ultrasonic atomizer with Ar/H2 carrier gas in a ratio of about 12/1. The synthesis of CNTs from a combination of two or three metallocenes reduces the percentage of metal catalyst impurity in the CNT sheet. However, there is an increase in structural defects in the CNTs when using mixtures of two or three metallocenes as catalysts. Furthermore, the specific electrical conductivity of the CNT sheet was highest when using a mixture of ferrocene and cobaltocene as the catalyst. Overall, the multi-catalyst method described enables tailoring certain properties of the CNT sheet. However, the standard ferrocene catalyst seems most appropriate for large-scale manufacturing at the lowest cost.

Correlation of EDLC Capacitance with Physical Properties of Polyethylene Terephthalate Added Pitch-Based Activated Carbon.

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s−1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance.

Melting dislocation transition in composite lithium greases with copper(II) carboxylate mesogenic additives

abstract We propose the theory for the temperature and concentration phase transformations in composite lithium grease doped with the mesogenic additives, copper(II) carboxylates valerate and isovalerate, in the range 1, 5, 10, 20 wt. %. The changes in specific electric conductivity manifested in dielectric spectroscopy in the measuring electric field of 100 Hz – 1 MHz and polarization microscopy are reliable caused by reversible transitions from the discotic to isotropic phase or at heating from room temperature to 391 K. To define critical properties of the transitions, we applied Monte Carlo simulations using the Berezinsky-Kosterlitz-Thouless model describing screw, transverse edge and longitudinal dislocations.

Pyrolysis temperature and feedstock affected Cr(VI) removal capacity of sulfidated zerovalent iron: Importance of surface area and electrical conductivity

Herein, feedstock (pinewood, rice straw, and dairy manure) and pyrolysis temperature (300, 500, and 700 °C) were selected as the influencing factors of properties of biochar (BC) to identify the contribution of biochar's matrix on Cr(VI) removal by BC-supported sulfidated zero-valent iron (S-ZVI/BC). Results showed that higher temperature was more conducible to improve the electrochemical properties and specific surface areas of composites. Raman spectra of S-ZVI supported by pinewood-derived BC (S-ZVI/PBC) showed the ID/IG ratio increased from 0.639 to 0.975 for the composites prepared at 300–700 °C, indicating the increased structural defects and resulting in the greatest Cr(VI) removal (35.81 mg g−1) and reduction (30.21 mg g−1) amounts of S-ZVI/PBC700. Besides, S-ZVI/PBC exhibited greater electrochemical reactivity and surface area than S-ZVI harbored by BC from dairy manure and rice straw. Additionally, Pearson correlation analysis revealed that Cr(VI) removal was significantly positively correlated to surface area (R2 = 0.90) and negatively correlated to Tafel corrosive potential (R2 = 0.88). Both desorption experiment and XPS spectra of spent sorbents showed that reduction predominated the detoxifying mechanism of Cr(VI) followed by adsorption (due to corrosively-generated iron oxides and BC) and precipitation (Cr2S3). This suggested that biochar with greater specific surface area and electrical conductivity is more favorable to immobilize S-ZVI with respect to Cr(VI) removal.

Tailoring Conductive 3D Porous Hard Carbon for Supercapacitors

Hard carbon has attracted great attention for energy storage owing to low cost and extremely high microporosity, however, hindered by its low electrical conductivity. The common strategy to improve the conductivity is through graphitization process which requires temperatures as high as 3000 °C and inevitably destroys the porous structure. Herein, a balance between the specific surface area and electrical conductivity in a 3D porous hard carbon by in situ iron‐catalyzed graphitization process together with the Si–O–Si network is successfully achieved. The Fe can accelerate the localized graphitization at relatively low temperature (1000 °C) to form nanographite domains with enhanced conductivity, while the Si–O–Si network contributes to generating a 3D porous structure. As a result, the optimized hard carbon exhibits a 3D interconnected and hierarchical porous structure with extremely high specific surface area (2075 m2 g−1) and excellent electrical conductivity (12 S cm−1) which is comparable with that of artificial graphite. And thus, high capacitance of 315 F g−1 and excellent rate capability (174 F g−1 at 40 A g−1) are simultaneously achieved when used as electrodes for supercapacitors. The strategy is promising to build hard carbon materials with well‐tuned properties for high‐performance energy storage.

Impacts of a mature forestry plantation on blanket peatland runoff regime and water quality

AbstractA lack of information concerning the hydrology and hydrogeology of intact blanket bogs limits current understanding of how their alteration to mature forestry plantations impacts stream flow and associated water quality. An integrated hydrological/hydrogeological monitoring programme compared processes operating in a relatively intact blanket peat‐covered catchment with conditions encountered in an adjacent area under closed canopy plantation forestry. Groundwater monitoring revealed contrasting water level regimes and deeper summer water tables in the afforested area, with forest groundwater also having more elevated specific electrical conductance (SEC) and containing higher concentrations of dissolved organic carbon (DOC). Near‐simultaneous pairwise runoff sampling at the relatively intact catchment and afforested catchment outlets demonstrated no significant difference in DOC concentration. Conversely, water samples from the afforested catchment outlet displayed significantly greater SEC; this arose in part because of higher concentrations of dissolved calcium and magnesium, discharging via artificial drainage. Comparison of base flow runoff SEC with peat groundwater samples reflected in significant contrasts in ionic signature and greater levels of mineralisation in surface water, pointing to contributions of deeper water, derived from inorganic substrate materials. Study findings indicate that disturbance to the ground in that part of the catchment under plantation forestry has led to greater variations in stream flow and water quality for aquatic ecosystems. Comparable conditions have been observed instreams flowing through plantation forestry in similar physical settings elsewhere. Study findings suggest that plantations on deep peat can adversely affect stream ecosystems and this may impact on a water body's legal status.

Effect of Nickel Precursor on the Catalytic Performance of Graphene Aerogel‐Supported Nickel Nanoparticles for the Production of COx‐free Hydrogen by Ammonia Decomposition

Graphene aerogel (GA), a promising porous material with high specific surface area and electrical conductivity, is utilized to disperse nickel nanoparticles to reach high catalytic activity in COx‐free hydrogen production from ammonia. Ni(NO3)2·6H2O and Ni (II) acetylacetonate (Ni(acac)2) were considered as metal precursors and the pH of the impregnation solution was varied to investigate the effects on the catalytic properties of the GA‐supported nickel catalysts. Data showed that the best dispersion and homogeneity, as well as the catalytic performance, is achieved with Ni(acac)2. An average Ni nanoparticle size of 13.6 ± 4.3 nm was obtained on the GA‐supported catalyst prepared by using Ni(acac)2 dissolved in an impregnation solution with a pH of 10.2. This catalyst with a Ni loading of 11.1 wt% provided an ammonia conversion of 70.2% at a space velocity of 30 000 mL NH3 gcat−1 h−1 and 600 °C corresponding to a hydrogen production rate of 21.5 mmol H2 gcat−1 min−1. Data illustrated that the difference between the point of zero charge of the support and the pH of the impregnation solution set by the type of the Ni precursor is a major parameter controlling the metal dispersion and the consequent catalytic activity.

Recent Applications of Carbon Nanotubes in Organic Solar Cells.

In recent years, carbon-based materials, particularly carbon nanotubes (CNTs), have gained intensive research attention in the fabrication of organic solar cells (OSCs) due to their outstanding physicochemical properties, low-cost, environmental friendliness and the natural abundance of carbon. In this regard, the low sheet resistance and high optical transmittance of CNTs enables their application as alternative anodes to the widely used indium tin oxide (ITO), which is toxic, expensive and scarce. Also, the synergy between the large specific surface area and high electrical conductivity of CNTs provides both large donor-acceptor interfaces and conductive interpenetrating networks for exciton dissociation and charge carrier transport. Furthermore, the facile tunability of the energy levels of CNTs provides proper energy level alignment between the active layer and electrodes for effective extraction and transportation of charge carriers. In addition, the hydrophobic nature and high thermal conductivity of CNTs enables them to form protective layers that improve the moisture and thermal stability of OSCs, thereby prolonging the devices’ lifetime. Recently, the introduction of CNTs into OSCs produced a substantial increase in efficiency from ∼0.68 to above 14.00%. Thus, further optimization of the optoelectronic properties of CNTs can conceivably help OSCs to compete with silicon solar cells that have been commercialized. Therefore, this study presents the recent breakthroughs in efficiency and stability of OSCs, achieved mainly over 2018–2021 by incorporating CNTs into electrodes, active layers and charge transport layers. The challenges, advantages and recommendations for the fabrication of low-cost, highly efficient and sustainable next-generation OSCs are also discussed, to open up avenues for commercialization.

Simple electrodeposition of 3D NiCoFe-layered double hydroxide nanosheet assembled nanospheres/nanoflowers on carbon cloth for high performance hybrid supercapacitors

Although layered double hydroxides (LDHs), especially NiCo-based LDHs, have been verified to be a type of potential cathode material for supercapacitors with high specific capacity and electric conductivity, their lifespan and rate performance are still not satisfactory. Herein, a series of 3D NiCoFe-LDH samples with different molar ratio of Ni/Co/Fe are successfully fabricated on carbon cloth via an electrodeposition method. It is found that NiCoFe-LDH nanosheet assembled nanospheres/nanoflowers electrode delivers high specific capacity, electrical conductivity, and more importantly, more superior rate performance as well as cycle stability than pristine NiCo-LDH electrode without Fe introduction. Moreover, the as-assembled hybrid supercapacitor device with NiCoFe-LDH and activated carbon as the cathode and anode respectively displays a wide voltage window (0–1.5 V), large specific energy (65 W h kg−1 at the specific power of 83 W kg−1) together with an ultrahigh cycle stability (26% capacity increment after 5000 cycles). With the merits of ease to fabricate and outstanding energy storage property, the newly assembled hybrid supercapacitor delivers great potential for practical application in the near future.

Моделювання та аналіз тривимірних квазистаціонарних електромагнітних полів безкон-тактних індуктометрів, розміщених над електропровідним ґрунтом сільськогосподар-ського призначення. Ч. ІІ.

The paper is devoted to solving the problem of the theory of three-dimensional quasi-stationary electromagnetic field generated by a non-contact inductometer in its interaction with the electrically conductive agricultural soil located below it at some distance and whose specific electrical conductivity is measured. The peculiarity of this study is that it is based on obtaining an accurate analytical solution to the problem of an electromagnetic field created by an arbitrary spatial circuit with a current (contactless inductometer model) located near a magnetized electrically conductive body with a flat surface (agricultural conductive soil model). Solutions made by taking into account the closed circuits are found in the form of squares for vector and scalar potentials, magnetic and electric field strengths in an electrically conductive medium without restrictions on the geometry of the circuits, environmental properties, and field frequency. Having a precise solution, in addition to the indisputable advantage associated with the validity of the results found, allows obtaining a number of consequences that are valid for an arbitrary field in the system. Another important consequence of an accurate solution is the conclusion that an inhomogeneous electromagnetic field when penetrating into an electrically conductive space with depth always attenuates faster than a homogeneous field. For pulsed fields, the calculation is limited to a certain period of time from the beginning of the current pulse, and the closer to the initial moment of time, the more accurately the electromagnetic field is calculated. Since the current pulse usually changes the fastest and reaches its highest values in a relatively short period of time, it is at this most important stage that the electromagnetic field is determined.