Surface Conductivity Research Articles

Quantitative Understanding of Ionic Channel Network Variation in Nafion with Hydration Using Current Sensing Atomic Force Microscopy.

Proton exchange membranes are an essential component of proton-exchange membrane fuel cells (PEMFC). Their performance is directly related to the development of ionic channel networks through hydration. Current sensing atomic force microscopy (CSAFM) can map the local conductance and morphology of a sample surface with sub-nano resolution simultaneously by applying a bias voltage between the conducting tip and sample holder. In this study, the ionic channel network variation of Nafion by hydration has been quantitatively characterized based on the basic principles of electrodynamics and CSAFM. A nano-sized PEMFC has been created using a Pt-coated tip of CSAFM and one side Pt-coated Nafion, and studied under different relative humidity (RH) conditions. The results have been systematically analyzed. First, the morphology of PEMFC under each RH has been studied using line profile and surface roughness. Second, the CSAFM image has been analyzed statistically through the peak value and full-width half-maximum of the histograms. Third, the number of protons moving through the ionic channel network (NPMI) has been derived and used to understand ionic channel network variation by hydration. This study develops a quantitative method to comprehend variations in the ionic channel network by calculating the movement of protons into the ionic channel network based on CSAFM images. To verify the method, a comparison is made between the NPMI and the changes in proton conductivity under different RH conditions and it reveals a good agreement. This developed method can offer a quantitative approach for characterizing the morphological structure of PEM. Also, it can provide a quantitative tool for interpretating CSAFM images.

Determining Liquid Limit and Plastic Limit of Clay Soils by Electrical Surface Conduction and Diffuse Double Layer Thickness

The aim of this study was to propose a new approach to determine the liquid limit and plastic limit of clay soils by considering electrical conductivity (EC) measurements. The proposed method included incorporating a new parameter, F, which is the ratio of the volumetric water contents of diffuse double layer (DDL) water and free water. In addition, the EC parameter, σ, was considered as the ratio of electrical surface conductivity and electrical conductivity of water. The changes in the thickness of DDL (χ) were also assessed to obtain corresponding equations to establish a connection with clay mineralogy, water content, and specific gravity in the final prediction. Three-dimensional surface analyses were conducted to find a correlation among F, σ, and χ to identify an appropriate method to predict liquid limit and plastic limit. The study was conducted with 39 different types of samples, and the outcomes from the EC approach were validated against the conventional methods. Overall, the coefficient of determination, R2 = 0.90, and Lin’s concordance correlation coefficient, (LCCC) = 0.91, were obtained for liquid limit prediction, whereas R2 = 0.64 and LCCC = 0.80 were obtained for plastic limit determination.

Influence of the Quantum Capacitance on Electrolyte Conductivity through Carbon Nanotubes.

In recent experiments, unprecedentedly large values for the conductivity of electrolytes through carbon nanotubes (CNTs) have been measured, possibly owing to flow slip and a high pore surface charge density whose origin remains debated. Here, we model the coupling between the CNT quantum capacitance and the classical electrolyte-filled pore one and study how electrolyte transport is modulated when a gate voltage is applied to the CNT. Our work shows that under certain conditions the quantum capacitance is lower than the pore one due to the finite quasi-1D CNT electronic density of states and therefore controls the CNT surface charge density that dictates the confined electrolyte conductivity. The dependence of the computed surface charge and conductivity on reservoir salt concentration and gate voltage is thus intimately related to the electronic properties of the CNT. This approach provides key insight into why metallic CNTs have larger experimentally measured conductivities than semiconducting ones.

Quantifying salinity in heterogeneous coastal aquifers through ERT and IP: Insights from laboratory and field investigations

The lithological and stratigraphical heterogeneity of coastal aquifers has a great influence on saltwater intrusion (SI). This makes it difficult to predict SI pathways and their persistence in time. In this context, electrical resistivity tomography (ERT) and induced polarization (IP) methods are receiving increasing attention regarding the discrimination between saltwater-bearing and clayey sediments. To simplify the interpretation of ERT data, it is commonly assumed that the bulk conductivity mostly depends on the conductivity of pore-filling fluids, while surface conductivity is generally disregarded in the spatial and temporal variability of the aquifers, particularly, once the aquifer is affected by the presence of saltwater. Quantifying salinities based on a simplified petrophysical relationship can lead to misinterpretation in aquifers constituted by clay-rich sediments. In this study, we rely on co-located data from drilled boreholes to formulate petrophysical relationships between bulk and fluid conductivity for clay-bearing and clay-free sediments. First, the sedimentary samples from the drilled wells were classified according to their particle size distribution and analyzed in the lab using spectral IP in controlled salinity conditions to derive their formation factors, surface conductivity, and normalized chargeability. Second, the deduced thresholds are applied on the field to distinguish clay-bearing sediments from brackish sandy sediments. The results are validated with logging data and direct salinity measurements on water samples. We applied the approach along the Luy River catchment and found that the formation factors and surface conductivity of the different unconsolidated sedimentary classifications vary from 4.0 to 8.9 for coarse-grained sand and clay-bearing mixtures, while normalized chargeability above 1.0 mS.m−1 indicates the presence of clay. The clay-bearing sediments are mostly distributed in discontinuous small lenses. The assumption of homogenous geological media is therefore leading to overestimating SI in the heterogeneous clay-bearing aquifers.

Carbon quantum dots modified and Y3+ doped Ni3 (NO3 )2 (OH)4 nanospheres with excellent battery-like supercapacitor performance.

Supercapacitor is an important energy storage device widely used in the automobile industry, military production, and communication equipment because of its fast charge-discharge rate, and high power density. Herein, carbon quantum dots modified and Y3+ doped Ni3 (NO3 )2 (OH)4 (NiY@CQDs) nanospheres are prepared by a solvothermal method and used as an electrode material. The electrochemical properties of NiY@CQDs were measured in a three-electrode system. An asymmetric supercapacitor (ASC) cell was assembled with activated carbon (AC) as the anode and NiY@CQDs as the cathode. The electrochemical properties of the ASC device were measured in a two-electrode system. Experimental results show the shape of NiY@CQDs is petal-shaped and the introducing carbon quantum dots and doping Y3+ significantly increases the specific surface area, conductivity, and specific capacitance of Ni3 (NO3 )2 (OH)4 . The mass-specific capacitance of NiY@CQDs reaches up to 2944 F g-1 at a current density of 1 A g-1 . The asymmetric supercapacitor of NiY@CQDs//AC has a high energy density of 138.65 Wh kg-1 at a power density of 1500 W kg-1 , displaying a wide range of application prospects in the energy storage area.

High-performance solid-state Li-ion batteries enabled by homogeneous, large-area ferroelectric PVDF-TrFE solid polymer electrolytes via horizontal centrifugal casting method

Solid polymer electrolytes (SPEs) have emerged as promising alternatives for enhancing the safety features of lithium-ion batteries (LIBs) while remaining compatible with established LIB manufacturing processes. However, a persistent challenge has been the relatively limited yield achieved via traditional fabrication techniques such as solution casting and doctor blade methods. In this study, we present a novel strategy to produce extensive and uniform films of solid polymer electrolytes using a ferroelectric polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) polymer. This approach employs horizontal centrifugal casting (HCC), a technique hitherto unutilized for SPE production. The substantial centrifugal forces generated during the HCC process yield SPE films characterized by uniform thickness across the surface and elevated ionic conductivity at ambient temperature. Compared to conventional solution casting techniques, the Li//Li cell featuring the SPE derived from HCC manifests stable electrochemical performance and increased cycle endurance. Additionally, a full cell incorporating a Li iron phosphate cathode displays consistent electrochemical behavior at room temperature. Notably, a 3 × 4 cm2 pouch cell maintains its performance attributes even under mechanical stress conditions such as folding and punching. These findings underscore the potential effectiveness of employing the HCC method in the development of high-performance SPE-based LIB systems.

Energy loss in practical waveguide channel designs

The presence of attenuation of electromagnetic waves in feeder paths leads to a decrease in the efficiency of radio engineering systems, as well as an increase in thermal noise, which reduces the sensitivity of the receiving part of the system. In addition to this, the thermal mode of the path deteriorates, which may be the cause of a decrease in its electrical strength, as well as overheating. For hollow rectangular waveguides, the loss value is determined by the following design characteristics: the internal dimensions of the cross section and the so-called microwave quality of the material in which the ultra-high frequency currents flow. For metallic waveguides microwave quality is characterized, first of all, by intrinsic conductivity and roughness of the inner surface. It should be emphasized that a necessary condition for a full-fledged study of the problem of loss reduction in waveguide devices is the possibility of practical substantiation of the results, specifically – the possibility of conducting measurements of losses in the layout of waveguide devices. However, in many works this issue is not given due attention, and any results of estimation of electrical parameters of conductive layers are not given. The purpose of this work is to study the magnitude of losses in practical designs of waveguide devices. The study is carried out on device layouts, conductive layers of which are made (formed) from common materials of high conductivity with different surface states. This paper presents the results of the study of effective conductivity values of practical waveguide channel designs. The research methodology showed acceptable accuracy (3...5%), and the research results are consistent with previously known data, as well as supplement them. The research results clearly demonstrate that such a widespread concept as the thickness (effective thickness) of the skin layer, obtained by calculation, is of practical importance only for ideal homogeneous materials. In other cases, the depth of occurrence and distribution of microwave current density is difficult to predict, depending on the coating thickness, roughness of the coating and the substrate, as well as on the ratio of their effective conductivities. Most publications on loss reduction in waveguide devices address the issues of surface microroughness. At the same time, in practical designs, attention should be paid to the condition of the surface layer. And it is peculiar not only for galvanic coatings, but also for surfaces obtained by cold deformation. Galvanic silver plating of the inner surface of brass waveguides used to increase electrical conductivity often does not give positive results due to the significant roughness and porosity of the silver coating. While the roughness can be improved (e.g. by mechanical means), reducing the porosity of the deposited metal represents a significant technological challenge.

Diammonium Phosphate Treatment for Sustained Hydraulic/Acid Fracture Conductivity in Chalk and Limestone Formations

Summary The sustained conductivity of hydraulic/acid fractures is crucial for the continuous and effective production of hydrocarbons. However, hydraulic fractures in soft carbonate formations often experience a reduction in conductivity due to rock deformation and creeping under in-situ stresses. One approach to resolve this issue is to stiffen the fracture surfaces using a consolidating agent. This study examines the application of diammonium hydrogen phosphate (DAP) as an additive to improve the hydraulic/acid fracture conductivity in Indiana limestone and Austin chalk slabs. Initially, flat slabs of Indiana limestone and Austin chalk were subjected to acidization using 15% and 10% hydrochloric acid (HCl) for 10 minutes and 5 minutes, respectively. The resulting surface texture changes were measured using a profilometer. Subsequently, half of the samples underwent treatment in 1 M DAP under 1,000 psi and 75°C for 72 hours. The surface stiffness of the samples was evaluated using nondestructive impulse hammering before and after acid injection and DAP treatment, while hydraulic/acid fracture conductivity was determined using an API conductivity setup. Following acid injection, the experimental results demonstrate that the stiffness of all the samples was diminished to different degrees. However, intact Indiana limestone samples exhibited increased stiffness after treatment with DAP. Acidized Indiana limestone samples showed partial restoration of their original stiffness with DAP treatment. In contrast, DAP treatment fully restored the stiffness of Austin chalk samples and further enhanced it, resulting in a twofold to fivefold increase. The increased stiffness observed in the treated samples had a direct impact on short- and long-term conductivity. Treated Indiana limestone fractures exhibited double the conductivity of untreated fractures. The improvement in Austin chalk conductivity was even more significant after DAP treatment, resulting in seven to eight times higher conductivity in the treated hydraulic/acid fractures. It is worth noting that there was little to no correlation between surface roughness and conductivity, highlighting the significant influence of fracture stiffness on conductivity.

Tuning of magnetosplamon coupling between graphene scatterers for the optimal design of adjustable metasurfaces

The resonance characteristics of magnetically-biased graphene micro-scatterers are thoroughly investigated in the present work using both eigenvalue and full-wave solvers. Initially, the graphene surface conductivity is presented in a tensor form due to the application of a magnetostatic bias field, which is perpendicular to the material’s surface. Then, the simple case of a graphene disk scatterer is examined, and a properly modified eigenvalue formulation is utilized to extract the plasmonic fundamental frequencies. The validity of the modal analysis is verified via a full-wave analysis that involves a plane-wave propagation and the extraction of the subsequent absorption cross-section utilizing the Finite-Difference Time-Domain method. Additionally, the dependence of a single disk scatterer resonances with the magnetostatic bias is evaluated, highlighting that as the bias field is increased, every edge mode degenerates into two sub-modes with an augmented difference between the resonant frequencies. Finally, the plasmonic coupling between adjacent scatterers is studied considering a periodic arrangement, similar to a metasurface, indicating the additional coupling modes as well as the adjustability of the properties with multiple degrees of freedom.

Fast Joule Heating for the Scalable and Green Production of Graphene with a High Surface Area.

The rapid development of electric vehicles, unmanned aerial vehicles, and wearable electronic devices has led to great interest in research related to the synthesis of graphene with a high specific surface area for energy applications. However, the problem of graphene synthesis scalability, as well as the lengthy duration and high energy intensity of the activation processes of carbon materials, are significant disadvantages. In this study, a novel reactor was developed for the green, simple, and scalable electrochemical synthesis of graphene oxide with a low oxygen content of 14.1%. The resulting material was activated using the fast joule heating method. The processing of mildly oxidized graphene with a high-energy short electrical pulse (32 ms) made it possible to obtain a graphene-based porous carbon material with a specific surface area of up to 1984.5 m2/g. The increase in the specific surface area was attributed to the rupture of the original graphene flakes into smaller particles due to the explosive release of gaseous products. In addition, joule heating was able to instantly reduce the oxidized graphene and decrease its electrical resistance from >10 MΩ/sq to 20 Ω/sq due to sp2 carbon structure regeneration, as confirmed by Raman spectroscopy. The low energy intensity, simplicity, and use of environment-friendly chemicals rendered the proposed method scalable. The resulting graphene material with a high surface area and conductivity can be used in various energy applications, such as Li-ion batteries and supercapacitors.

Research on Singularity in Calculation of Induced Electric Field in Pointed Conductors

In the electric field environment of thunderstorm, the tip of a grounded object at a high place is more likely to produce corona discharge and finally cause lightning flash. Therefore, the study of the surface electric field of the grounded object tip in the electric field environment has important theoretical value and practical significance for the analysis of the characteristics of the head-on discharge. Due to the strong singularity of the tip structure, the traditional numerical analysis method cannot accurately calculate its surface electric field. Therefore, the traditional literature usually chamfers the conductor tip, but in lightning physics, researchers are most concerned about the maximum field strength in the local area. In order to study the electric field distribution on the tip conductor surface, a semi-analytical boundary element method is proposed to calculate the tip structure directly. Firstly, the analytical formula of the electric field on the tip conductor surface and the boundary element semi-analytical common method are derived, and the tip conductor model is established to calculate the tip electric field excited by the external electric field using the analytical solution and the semi-analytical method. The correctness of the semi-analytical method is verified by calculating the L2 loss function of the two, and the influence of the tip angle on the semi-analytical calculation results is studied. The results show that for the three-dimensional cone model, the L2 loss function is 10-5, which meets the calculation accuracy. The special treatment of the semi-analytical method at the strong singular integral makes the calculation accuracy much higher than that of the Gaussian integral, where the L2 loss function is greatly reduced. Further, based on the change of tip angle, as the conductor tip becomes sharper, the greater the electric field distortion is, and the greater the L2 loss function is. The research results provide a method reference for the calculation of the electric field on the tip conductor surface.

An Experimental Study on EMI Shielding and Antibacterial Activity of Woven Fabrics Including Silver Nanocomposite Yarns

This study investigates electromagnetic interference shielding and antibacterial activity of industrial polyester/viscose woven fabrics, including silver (Ag) treated yarns, to obtain multifunctional fabric. For this purpose, thin film-coated, nanoparticle-doped, and chemically treated yarns were used as weft in three different densities. Nine fabric samples and the control sample were woven under industrial conditions. As a result, the surface conductivity of the thin film-coated samples is significantly higher than the others in all the measurement directions. Also, these samples exhibit the best electromagnetic shielding efficiency of up to 64 dB in the 3–43 GHz frequency range. In addition, electromagnetic shielding efficiency reaches 83 dB when the samples are measured in multiple layers. The chemically treated samples exhibited better antibacterial activity, up to 74%. It was determined that the nanoparticle’s treatment type, position and density, and the number of fabric layers influence the performance properties.

Fabrication of cervical squamous cell carcinoma antigen immunosensor using graphene-polymer composites

An ultrasensitive electrochemical immunosensor was developed for detection of the cervical squamous cell carcinoma antigen (SCCA) biomarker using graphene-chitosan nanocomposites. Graphene oxide (GO) synthesized by a modified Hummer’s method was functionalized with chitosan biopolymer (CS) to produce CS-GO nanocomposites. Characterization by SEM, FTIR, Raman, XPS confirmed successful grafting of CS onto GO by electrostatic interactions. The CS-GO composite exhibited improved conductivity and biocompatibility. After optimizing the GO:CS ratio to 1:1, the nanocomposite was deposited on glassy carbon electrodes (GCE). Anti-SCCA antibodies were then immobilized covalently using pyrenebutyric acid crosslinker. The immunosensor fabrication was analyzed by EIS, CV, and DPV electrochemical techniques. The conditions including CS-GO ratio, antibody concentration, incubation time, pH, and voltage parameters were systematically optimized using orthogonal experimental design. Under optimal conditions, the immunosensor showed a linear detection range from 1 pg/mL to 100 ng/mL with a sensitivity of 196 μA/(ng/mL/cm2). The low limit of detection of 1 pg/mL was attributed to the high surface area and conductivity of the CS-GO transducer. Analysis of human serum samples spiked with SCCA demonstrated the reliability of the immunosensor for clinical applications. The graphene-nanocomposite electrochemical biosensing platform provides a rapid, low-cost, and ultrasensitive alternative to ELISA for SCCA detection in cervical cancer diagnostics.

Investigation of high resistivity [formula omitted]-type FZ silicon diodes after 60Co [formula omitted]-irradiation

In this work, the effects of 60Co γ-ray irradiation on high resistivity p-type diodes have been investigated. The diodes were exposed to dose values of 0.1, 0.2, 1, and 2MGy. Both macroscopic (I–V, C–V) and microscopic investigations, by means of Thermally Stimulated Current (TSC) and Deep Level Transient Spectroscopy (DLTS) techniques, were conducted to characterize the radiation-induced changes. The investigated diodes were manufactured on high resistivity p-type Float Zone (FZ) silicon and were further classified into two types based on the isolation technique between the pad and guard ring: p-stop and p-spray. After irradiation, the macroscopic results of current–voltage and capacitance–voltage measurements were obtained and compared with existing literature data. Additionally, the microscopic measurements focused on the development of the concentration of different radiation-induced defects, including the Boron interstitial-Oxygen interstitial (BiOi) complex, the Carbon interstitial-Oxygen interstitial (CiOi) defect, the H40K, and the so-called IP∗.To investigate the thermal stability of induced defects in the bulk, isochronal annealing studies were performed in the temperature range of 100°C to 300°C. These annealing processes were carried out on diodes irradiated with doses of 1 and 2MGy. Furthermore, in order to investigate the unexpected results observed in the C–V measurements after irradiation with high dose values, the surface conductance between the pad and guard ring was measured as a function of both dose and annealing temperature.

Electromagnetic TE- and TM-waves propagation in a plane waveguide covered with graphene characterized by nonlinear conductivity

Background. Guiding properties of waveguiding structures with graphene are of great importance for various applications and have been studied in many papers. In all such studies, graphene was characterized, as a rule, by linear surface conductivity. However, if the intensity of an electromagnetic wave is large enough, the interaction of graphene with the electromagnetic wave becomes nonlinear; in this case, it is more correct to describe graphene by nonlinear conductivity.
 Aim. This work is aimed at studying the influence of cubic nonlinearity of graphene, corresponding to the so-called self-action effects (not affecting the frequency of the incident wave), on the propagation of TE- and TM-polarized waves in the structure, which is a plain dielectric layer covered on one side by graphene.
 Methods. In this study, the guiding properties of the waveguide are studied using primarily an analytical approach. Thus, from Maxwell's equations, material equations and boundary conditions, a couple of dispersion equations for TE-and TM-polarized waves is derived and then its solvability is studied. In addition, some numerical experiments are carried out in the study.
 Results. The dispersion equations of the studied waveguiding structure for TE- and TM-polarized waves are derived in explicit form. Studying analytically obtained equations, conditions for waveguide parameters are found, providing the existence of a given number of waveguide modes. In addition, some numerical results are obtained in the paper, which give an idea of the influence of nonlinear effects on the electromagnetic waves propagating in the structure.
 Conclusion. The results obtained in this paper reveal two effects related to the cubic nonlinearity of graphene. Firstly, in a plain dielectric layer with graphene coating in the strong nonlinear regime TE-waves with longer wavelength and TM-waves with shorter wavelength propagate compared to electromagnetic waves that propagate in the same structure in the linear regime. Secondly, the strong cubic nonlinearity leads to a greater localization of the electromagnetic wave within the waveguiding structure.

Rhamnolipids‐based glycosylated coating for preparing non‐charging polymeric materials surfaces

AbstractPolymer materials are typical insulators that are easily charged by contact electrification. Static charge generated by contact electrification on their surfaces can lead to lots of undesirable consequences, including a reduction in efficiency of manufacturing processes, damage to equipment, and even explosions. Thus, it is important to develop effective strategies to prevent the generation of static charge when surfaces of polymer materials come into contact. Here, we coated polymer materials with rhamnolipids (RLs) to create non‐charging surfaces. This innovative technique, based on glycosylated coatings using RLs, offers a universal solution that can be easily applied to a wide range of polymeric materials conferring resistance to surface charging via contact electrification. The amount of static charges generated was found to reduce dramatically in both low (~15%) and high (~60%) humidity situations. The reduction of charge is due to either or both of the following two mechanisms: by increasing surface conductivity driven by the hydrophilic groups of the RLs molecules, and or by their radical‐scavenging properties. Predictably, this new effective strategy is ideal for producing antistatic dipping and spray solution for various practical applications.

On the behavior of sub-micrometer polystyrene particles subjected to AC insulator-based dielectrophoresis.

Polymer beads, especially polystyrene particles, have been extensively used as model species in insulator-based dielectrophoresis (iDEP) studies. Their use in alternating current iDEP (AC-iDEP) is less explored; however, an assessment in the low-frequency regime (≤10kHz) allows to link surface conduction effects with the surface properties of polymer particles. Here, we provide a case study for various experimental conditions assessing sub-micrometer polystyrene particles with AC-iDEP and link to accepted surface conduction theory to predict and experimentally verify the observed AC-iDEP trapping behavior based on apparent zeta potential and solution conductivity. We find excellent agreement with the theoretical predictions, but also the occurrence of concentration polarization electroosmotic flow under the studied conditions, which have the potential to confound acting dielectrophoresis conditions. Furthermore, we study a case relevant to the assessment of microplastics in human and animal body fluids by mimicking the protein adsorption of high abundant proteins in blood by coating polystyrene beads with bovine serum albumin, a highly abundant protein in blood. Theoretical predictions and experimental observations confirm a difference in observed AC-iDEP behavior between coated and non-coated particles, which might be exploited for future studies of microplastics in blood to assess their exposure to humans and animals.

Energy partitioning and controlling factors of evapotranspiration in an alpine meadow in the permafrost region of the Qinghai-Tibet Plateau

Abstract Energy partitioning and evapotranspiration (ET) of alpine meadows in permafrost areas are crucial for water cycle on the Qinghai-Tibet Plateau. However, seasonal (freeze–thaw cycle) variations in energy partitioning and ET and their driving factors must be clarified. Therefore, 4-year energy fluxes [i.e. latent heat (LE) and sensible heat (H)] were observed, and bulk parameters [i.e. surface conductance, decoupling coefficient (Ω), and Priestley–Taylor coefficient (α)] were estimated in an alpine meadow in the Qinghai-Tibet Plateau. Mean daily LE (27.45 ± 23.89 W/m2) and H (32.51 ± 16.72 W/m2) accounted for 31.71% and 50.14% of available energy, respectively. More available energy was allocated to LE during the rainfall period, while 67.54 ± 28.44% was allocated to H during the frozen period. H was half the LE during rainfall period and seven times the LE during frozen period due to low soil water content and vegetation coverage during the frozen season. Mean annual ET was 347.34 ± 8.39 mm/year, close to mean annual precipitation. Low mean daily Ω (0.45 ± 0.23) and α (0.60 ± 0.29) throughout the year suggested that ET in the alpine meadow was limited by water availability. However, ET was constrained by available energy because of sufficient water supply from precipitation during rainfall season. In contrast, large differences between ET and precipitation indicated that soil water was supplied via lateral flow from melting upstream glaciers and snow during the transition season. The results suggest that seasonal variations in bulk parameters should be considered when simulating water and energy fluxes in permafrost regions.

In-situ grown nickel iron bimetal organic frameworks from activated Ni foam for efficient energy storage and electrocatalysis: Study of metal ratio and nickel precursor effects

Ex-situ fabrication of electroactive electrodes encounters serious peeling off problems. Nickel foam (NF) shows promise as conductive substrate of electroactive electrodes due to high surface area, porosity and conductivity. To broaden NF applications and enhance attachments, applying in-situ growth for establishing efficient active materials on NF is necessary. In this study, nickel iron bimetal organic frameworks (NiFeMOF) are firstly synthesized from activated NF as electroactive electrodes for energy storage and electrocatalysis. Metal ratio and nickel precursor effects are studied to elucidate growing mechanism of electroactive materials. The optimal NiFeMOF/NF presents the highest specific capacitance (CF) of 2017.9 F/g at 20 mV/s, while MOF/NF electrodes prepared with only Ni and Fe respectively show smaller CF values of 622.1 and 1121.8 F/g. The superior electrocatalytic ability is achieved by NiFeMOF/NF. Inclusion of additional Ni salts is necessary for synthesizing Ni-MOF on NF with improved energy storage ability, but that prepared without addition of Ni salt exhibits better electrocatalytic ability. Trade-off between electrochemical surface area and electrical conductivity is proved as crucial factor in designing electroactive materials for energy storage and electrocatalytic water splitting. This study brings novel insights into establishment of effective electroactive materials for electrochemical systems using simple concepts and techniques.

Exploring limitations in the induced polarization versus surface conductivity relationship in the case of wetland soils

Recent induced polarization studies suggest that the real part of surface conductivity ([Formula: see text]) scales linearly with the imaginary conductivity ([Formula: see text] = [Formula: see text]) or normalized chargeability (Mn) for a range of soil types. The coefficients of this relationship l and l_Mn ( l = [Formula: see text]/[Formula: see text] or l_Mn = Mn/[Formula: see text]) allow the separation of the surface and electrolytic conductivities from the bulk conductivity. However, the dependence of these constants on varying soil physicochemical properties, including under unsaturated conditions, is yet to be assessed. Using estimates of [Formula: see text] from 18 undisturbed soil samples from a restored wetland and [Formula: see text] measured over a frequency range of 0.01 Hz to 10 kHz, the [Formula: see text] and [Formula: see text] were compared with the laboratory measurements of soil properties. Also, l and l_Mn were calculated for each soil sample and regressed them against the soil properties. We find an apparent dependence of l on soil texture, bulk density, organic matter, and moisture contents, with coefficients of determination ([Formula: see text]) ranging from 0.5 to 0.65 at low frequencies (e.g., 1 Hz) but not at high frequencies (e.g., 936 Hz). This dependence of l on soil texture results from the insensitivity of [Formula: see text] at low frequency to [Formula: see text] and, by implication, to the soil properties controlling [Formula: see text]. In contrast, l_Mn indicates no correlation with the soil properties because Mn is linearly correlated with [Formula: see text] and correlated with the soil properties controlling [Formula: see text]. Our results call for caution on the application of [Formula: see text] at a single frequency as a proxy of [Formula: see text] because [Formula: see text] is not necessarily correlated with [Formula: see text] across all soil types. Although using l_Mn derived from multifrequency measurements overcomes this limitation, field acquisition of spectral information (e.g., up to 1000 Hz) remains a challenge.