Active Edge Research Articles

Enhanced performance of UV photodetector of MoS2 quantum dots-decorated ZnO nanorods

Two-dimensional transition metal dichalcogenides such as molybdenum disulfide (MoS2) have attracted great attention due to their unique optical, electrical and chemical properties. MoS2 quantum dots (QDs) exhibit strong quantum confinement, high surface area and notable active edge sites compared to their bulk. In this work, MoS2 QDs were attached on the surface of ZnO nanorods (NRs) grown on interdigitated ITO substrates and then used as photodetector. MoS2 QDs were synthesized by a new ultrafast way pulsed laser ablation (PLA) in liquid method and then spincoated on the surface of ZnO NRs. The pristine ZnO and ZnO/MoS2 QDs photodetector were investigated under UV and visible light (325 nm, 505 nm and 635 nm) with the bias voltage -5 V to 5 V. The results show that the decoration of ZnO NRs by MoS2 QDs could enhance the sensitivity, responsivity and detectivity under UV irradiation. This may due to the decrease of dark current as the result of passivation of surface defects of ZnO NRs by MoS2 QDs.

Spreader events and the limitations of projected networks for capturing dynamics on multipartite networks.

Many systems of scientific interest can be conceptualized as multipartite networks. Examples include the spread of sexually transmitted infections, scientific collaborations, human friendships, product recommendation systems, and metabolic networks. In practice, these systems are often studied after projection onto a single class of nodes, losing crucial information. Here, we address a significant knowledge gap by comparing transmission dynamics on temporal multipartite networks and on their time-aggregated unipartite projections to determine the impact of the lost information on our ability to predict the systems' dynamics. We show that the dynamics of transmission models can be dramatically dissimilar on multipartite networks and on their projections at three levels: final outcome, the magnitude of the variability from realization to realization, and overall shape of the temporal trajectory. We find that the ratio of the number of nodes to the number of active edges over the time-aggregation scale determines the ability of projected networks to capture the dynamics on the multipartite network. Finally, we explore which properties of a multipartite network are crucial in generating synthetic networks that better reproduce the dynamical behavior observed in real multipartite networks.

A review on mechanisms and recent developments in p-n heterojunctions of 2D materials for gas sensing applications

2D materials and their heterojunctions have been explored for gas sensing applications due to their tremendous surface-to-volume ratio, active edges with atomic thickness, and tunable electrical properties. Heterostructures of 2D materials exhibit absolutely novel physics and versatility with accelerated device performance by integrating the atomic scale properties of individual materials. Traditional gas sensors use homogeneous materials as the sensing interface in which the surface adsorbed oxygen ion species play an important role in its performance. But the performance of the sensors suffers greatly due to their selectivity and high working temperature leading to poor stability and short-term uses; the van der Waals 2D p-n heterojunction-based gas sensors hold several advantages since both the materials and the depletion layer formed at the junction can actively tune the sensing performance. By choosing 2D materials with different band structures, charge polarity, carrier concentration, and work function, band alignment at the interface can be precisely engineered to achieve the selective gas sensing performance with low operating temperature. Herein, we have reviewed the working principles, recent developments, and future perspectives of p-n heterojunctions of 2D materials for gas sensing applications.

NiCo layered double hydroxides derived Ni0.67Co0.33(PO3)2 as stable and efficient electrocatalysts for overall water splitting

Abstract The synthesis of highly efficient non-noble bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the same electrolyte is important for the industrial application of electrocatalytic water splitting. Herein, non-noble bifunctional electrocatalyst Ni0.67Co0.33(PO3)2 nets with optimized morphology were successfully synthesized. Owing to the micropores with the accelerated electrolyte and gases transfer and nanopores architecture with more exposed active edge sites, the self-supported Ni0.67Co0.33(PO3)2-12 h electrode exhibits a superior water splitting performance. Impressively, the Ni0.67Co0.33(PO3)2-12 h electrode only needs a cell voltage of 1.46 V to achieve 10 mA/cm2 and shows over 22 h stability at 10, 50 and 100 mA/cm2, respectively. This present work suggests a unique and earth abundant material synthesis method for water electrolysis, which has broad prospects for practical water splitting application.

Review of Vertical Graphene and its Applications.

Vertical graphene (VG) is a thin-film complex material featuring hierarchical microstructures: graphene-containing carbon nanosheets growing vertically on its deposition substrate, few-layer graphene basal layers, and chemically active atomistic defect sites and edges. Thanks to the fundamental characteristics of graphene materials, e.g. excellent electrical conductivity, thermal conductivity, chemical stability, and large specific surface area, VG materials have been successfully implemented into various niche applications which are strongly associated with their unique morphology. The microstructure of VG materials can be tuned by modifying growth methods and the parameters of growth processes. Multiple growth processes have been developed to address faster, safer, and mass production methods of VG materials, as well as accommodating various applications. VG's successful applications include field emission, supercapacitors, fuel cells, batteries, gas sensors, biochemical sensors, electrochemical analysis, strain sensors, wearable electronics, photo trapping, terahertz emission, etc. Research topics on VG have been more diversified in recent years, indicating extensive attention from the research community and great commercial value. In this review article, VG's morphology is briefly reviewed, and then various growth processes are discussed from the perspective of plasma science. After that, the most recent progress in its applications and related sciences and technologies are discussed.

Fabrication of PVDF-based piezocatalytic active membrane with enhanced oxytetracycline degradation efficiency through embedding few-layer E-MoS2 nanosheets

A novel piezocatalytic active membrane based on mixed matrix of exfoliated multi-flaw MoS2 (E-MoS2) nanosheets and polyvinylidene fluoride (PVDF) was synthesized by electrospinning technique. The composition and structure of the obtained E-MoS2/PVDF electrospun fiber membranes (EFMs) were characterized via FESEM, HR-TEM, XRD, FTIR and XPS techniques. The piezocatalytic activity of the EFMs was evaluated by the degradation of antibiotic oxytetracycline (OTC) under ultrasonic irradiation in the dark. The 10.0 wt% E-MoS2/PVDF EFMs exhibited superior OTC degradation efficiency of 93.08% within 24 min with pseudo-first-order kinetic constant (k) of 0.09124 min−1, which was 21.1 times higher than that of the pure PVDF EFMs. The superior performance was attributed to the synergetic effect of the embedded E-MoS2 nanosheets and a high proportion of PVDF β-phase (94.1%) to effectively improve the piezoelectric property of composite. In addition, the ultrathin multi-flaw structure of E-MoS2 provided abundant catalytic active edge sites and increased the surface charge density, promoting the generation of more ∙OH and ∙O2– radicals to degrade OTC pollutants. The degradation intermediates of OTC over 10 wt% E-MoS2/PVDF EFMs were detected by HPLC–MS and two main degradation pathways were reasonably proposed. The piezocatalytic activity of 10 wt% E-MoS2/PVDF EFMs remained stable after five consecutive cycles. This study is meaningful for exploring the composite membrane piezocatalysts for largescale applications in wastewater treatment.

Applications of high-resolution scanning probe microscopy in hydroprocessing catalysis studies

Scanning probe microscopy offers real space atomic and nanoscale imaging of surfaces and supported nanoparticles, and these techniques are used in a planar catalyst model system context to analyze important atomic-scale aspects of nanoparticle structure, particle edges, defects, vacancies and to image the resulting interaction of individual reactants with the active surfaces. Here we review applications of high-resolution scanning probe microscopy to hydroprocessing catalysis, to demonstrate how these atom-resolved imaging techniques have recently advanced to become tools that elucidate the catalytically active edge structures of metal sulfide hydrotreating catalyst, resolve the intramolecular structure of complex hydrocarbons, and provide atomic-scale information on the mechanisms in which heteroatom-bearing hydrocarbons interact with a catalyst particle. This mini-review addresses the advantages of scanning tunneling microscopy for studies of planar model systems relevant for hydroprocessing catalysis, including the emerging use of near-ambient pressure (operando) scanning tunneling microscopy together with examples of the use of low-temperature molecular imaging with non-contact atomic force microscopy.

Granular Polymeric Carbon Nitride with Carbon Vacancies for Enhanced Photocatalytic Hydrogen Evolution

Considering the high charge recombination rate, low optical adsorption intensity and limited active sites greatly constrict the solar‐to‐chemical conversion efficiency of polymer carbon nitride. Herein, a facile approach is reported to produce defected polymeric carbon nitride (PCN) with abundant granular bulks with fractured boundaries by thermal reduction treatment in CO atmosphere. The photocatalytic hydrogen evolution over defected PCN exhibits a rate of 3281.2 μmol g−1 h−1, 3.5 times higher than the pristine, which is most possibly ascribed to the following factors. The unique defected and porous structure not only provides higher specific surface area, more exposed active edges, abundant charge separation sites, and active centers for hydrogen generation but also is beneficial to rapid mass and charge transfer, interior diffusing of incident light, and shortening carrier transport length, thus enhancing the optical adsorption and accelerating the photocatalytic reaction kinetics. Furthermore, the electron delocalization at carbon vacancies sites on one hand facilitates the separation rate of electron–hole pairs and prolonged the carrier lifetime; on the other hand, the electronic polarization caused by C atoms loss helps increasing the affinity between catalyst and substrate reactant. Moreover, the higher electron donor density and lower conduction band minimum (CBM) potential further enhance the reduction capacity for H2 evolution.

Gamma Radiation-Induced Oxidation, Doping, and Etching of Two-Dimensional MoS2 Crystals.

Two-dimensional (2D) MoS2 is a promising material for future electronic and optoelectronic applications. 2D MoS2 devices have been shown to perform reliably under irradiation conditions relevant for a low Earth orbit. However, a systematic investigation of the stability of 2D MoS2 crystals under high-dose gamma irradiation is still missing. In this work, absorbed doses of up to 1000 kGy are administered to 2D MoS2. Radiation damage is monitored via optical microscopy and Raman, photoluminescence, and X-ray photoelectron spectroscopy techniques. After irradiation with 500 kGy dose, p-doping of the monolayer MoS2 is observed and attributed to the adsorption of O2 onto created vacancies. Extensive oxidation of the MoS2 crystal is attributed to reactions involving the products of adsorbate radiolysis. Edge-selective radiolytic etching of the uppermost layer in 2D MoS2 is attributed to the high reactivity of active edge sites. After irradiation with 1000 kGy, the monolayer MoS2 crystals appear to be completely etched. This holistic study reveals the previously unreported effects of high-dose gamma irradiation on the physical and chemical properties of 2D MoS2. Consequently, it demonstrates that radiation shielding, adsorbate concentrations, and required device lifetimes must be carefully considered, if devices incorporating 2D MoS2 are intended for use in high-dose radiation environments.

Increasing the Hot‐Electron Driven Hydrogen Evolution Reaction Rate on a Metal‐Free Graphene Electrode

AbstractRecently, it has been shown that a semiconductor–insulator–graphene device can drive the hydrogen evolution reaction (HER) at the graphene surface with a reduced onset potential by injecting hot electrons into graphene. However, the catalytic properties of graphene are limited by the large hydrogen adsorption energy and lack of electrochemically active sites. To address these limitations, a n‐silicon/insulator/plasma etched graphene device is investigated, where a dry etch process is used to increase the number of active sites on the graphene by creating a greater number of active edge sites, increasing hydrogen adsorption at a given potential. This has been shown to improve the properties of devices with cold electrons. However, here it is shown that this approach can improve the HER rate with hot electrons. The electrons injected into the graphene from the silicon shift the onset potential of HER by as high as ≈0.8 V reaching a current density of 90 mA cm−2 at an overpotential of ‐0.5 V versus RHE. Furthermore, the comparison between device with pristine graphene shows a ≈2X improvement in current density at high overpotentials. This result shows that hot‐electron devices can be improved by modifying the catalytically active sites without metal catalysts.

Vertically Aligned MoS2 with In-Plane Selectively Cleaved Mo-S Bond for Hydrogen Production.

Perturbing the periodic electronic structure of the MoS2 basal plane via vacancy engineering offers an opportunity to explore its intrinsic activity. A significant challenge is the design of vacancy states, which include its type, distribution, and accessibility. Here, well-dispersed and vertically aligned MoS2 nanosheets with an in-plane selectively cleaved Mo-S bond on a carbon matrix (c-MoS2-C) have been prepared by a self-engaged strategy, which synergistically realizes uniform vacancy manufacturing and three-dimensional (3D) self-assembly of the defective MoS2 nanosheets. X-ray adsorption spectroscopy investigation confirms that the cleaved MoS2 basal plane generates newly active edge sites, where the Mo centers feature unsaturated coordination geometry. Theoretical calculations reveal that the exposed interior edge Mo sites represent new active centers for hydrogen adsorption/desorption. As expected, the synthesized c-MoS2-C exhibits markedly enhanced hydrogen evolution activity and superior stability. This in-plane activation strategy could be extended to other types of transition-metal dichalcogenides and catalytic reaction systems.

Contact Engineering of Vertically Grown ReS2 with Schottky Barrier Modulation.

Forming metal contact with low contact resistance is essential for the development of electronics based on layered van der Waals materials. ReS2 is a semiconducting transition metal dichalcogenide (TMD) with an MX2 structure similar to that of MoS2. While most TMDs grow parallel to the substrate when synthesized using chemical vapor deposition (CVD), ReS2 tends to orient itself vertically during growth. Such a feature drastically increases the surface area and exposes chemically active edges, making ReS2 an attractive layered material for energy and sensor applications. However, the contact resistances of vertically grown materials are known to be relatively high, compared to those of common 2H-phase TMDs, such as MoS2. Most reported methods for lowering the contact resistance have been focused on exfoliated 2H-phase materials with only a few devices tested, and few works on distorted T-phase materials exist. Moreover, nearly all reported studies have been conducted on only a few devices with mechanically exfoliated fl Most reported methods for lowering the contact resistance have been 2 contacts was modulated by conformally coating a thin tunneling interlayer between the metal and the dendritic ReS2 film. Over a hundred devices were tested, and contact resistances were extracted for large-scale statistical analysis. Importantly, we compared various known materials and techniques for lowering contact resistance and found an optimized method. Finally, the reductions in barrier height were directly correlated with exponential reductions in contact resistance and increases in drive-current by almost 2 orders of magnitude.

Hierarchical fibrous bimetallic electrocatalyst based on ZnO-MoS2 composite nanostructures as high performance for hydrogen evolution reaction

To understand new fundamental questions related to electrocatalyst design to achieve very efficient and stable nonprecious catalysts for water splitting and to strengthen renewable energy reservoirs and nonprecious nanocomposites for efficient water splitting will strengthen the renewable energy reservoirs, thereby it will bring more sustainable and environment friendly society with minimum global warming effect. The synthesized nanocomposite material demonstrates efficient catalytic kinetics for HER, due to the exposure of best active edge sites of MoS 2. The as prepared the nanocomposite was characterized successfully by XRD, SEM, TEM, XPS & EDS were executed that elucidates the crystalline nature of the synthesized nanocomposite material. In an acidic medium, ZnO 30% providing the best ZnO-MoS 2 content achieved at 0.26 V. The ZnO-MoS 2 Tafel slope is 56 mV/decades the ever reported for hydrogen production in an acidic media for ZnO-MoS 2 -based electrocatalysts. The electrocatalyst exhibit excellent stability and durability. Chronopotentiometry at 10 mA/cm 2 current density suffers not a significant loss in the potential for 10 h in an acidic media, respectively. The sample of less ZnO concentration results in increased catalytic properties for MoS 2 , by providing active basal planes for hydrogen evolution reaction along with Mo and S-edges, as predicted by theoretical studies. Interestingly, the catalyst material, architecture and use of nanostructured catalysts have been found useful for improving the efficiency by showing high active reaction sites and the electrical connection of these sites for swift charge kinetics. Therefore, the morphology and structure of fabricated electrocatalysts can have advantageous features for catalysis performance. These findings provide a new stable and efficient electrocatalysts for the development of electro catalyzer devices for the hydrogen gas production based on cost-effective methodology and earth-abundant materials. This work will open a new gateway for the development of functional catalysts in renewable energy reservoirs, which will be scientifically significant and will also provide a roadmap for the development of industrial catalysts.

Appropriate use of dissolved gas energy in fields at the final stage of development

In order to improve the development of fields at a later stage, this article considered the use of water-gas repression together with the dissolved gas energy. The theoretical basis of the study is based on the application of the method of physical modeling of oil displacement by water. As a result, it was found that waterflooding would be more effective when such an activity is carried out in the early stages of development. Waterflooding can also be effective in old, depleted fields with shallow depths of oil-bearing horizons. The article states that in flooded deposits, where the reservoir pressure did not drop below the bubble point pressure, it is advisable to reduce the reservoir pressure to the bubble point pressure (to carry out forced withdrawal). After that, water injection should be resumed with 30-50% compensation. It has been established that in order to increase the efficiency of the development of fields developed in the dissolved gas mode, waterflooding must be started at a reservoir pressure that is 30–70% less than the bubble point pressure. The best option for the development of such deposits is the presence of active edge waters. If they are absent, it is advisable to end water in the aquifer with compensation of withdrawals from 20 to 40% after the start of gas extraction from oil.

Rapid hydrothermal synthesis of highly crystalline transition metal (Mn & Fe) doped CuSe nanostructures: Applications in wastewater treatment and room temperature gas sensing

In this paper, we report on the rapid hydrothermal synthesis of CuSe 2D nanocrystals. The nanostructures were synthesized for very short reaction durations of 3 h. The influence of two different transition metal inclusions (Mn & Fe) on the growth and properties of CuSe nanocrystals was investigated. Transition metal dopants were found to have a prominent influence on the morphological, magnetic, optical and photocatalytic behavior of the material. Structural properties show that the nanostructures have a single phase with the hexagonal structure. The inclusion of the transition metal dopants (Mn and Fe) had no influence on the phase of the nanostructures although growth along certain crystal directions was restricted. Morphologies like flakes and hexagonal discs were obtained, all in the nanoscale dimensions. Doping resulted in the development of catalytically active edge sites which are more prominent in the case of Fe doping. Magnetic studies reveal conversion of diamagnetic CuSe into paramagnetic material upon doping with Fe and Mn. The gas sensing property of the synthesized nanostructures was tested against NO2 gas. The hexagonal nano-discs showed the highest sensitivity reaching 25% at 40 ppm NO2 concentration. The nanostructures were utilized for the photodegradation of methylene blue (MB) dye under UV-Visible light illumination. Addition of the transition metal dopants resulted in the enhancement of photocatalytic activity of the material, improving the degradation percentage from 59.4% to 64.5%.

Front Cover: Active Edge Site Exposed β‐Ni(OH)2 Nanosheets on Stainless Steel Mesh as a Versatile Electrocatalyst for the Oxidation of Urea, Hydrazine, and Water (ChemCatChem 4/2021)

Front Cover: Active Edge Site Exposed β‐Ni(OH)₂ Nanosheets on Stainless Steel Mesh as a Versatile Electrocatalyst for the Oxidation of Urea, Hydrazine, and Water (ChemCatChem 4/2021)

Hydrogen and Potassium Acetate Co-Production from Electrochemical Reforming of Ethanol at Ultrathin Cobalt Sulfide Nanosheets on Nickel Foam.

The sluggish reaction kinetics of the anodic oxygen evolution reaction increases the energy consumption of the overall water electrolysis for high-purity hydrogen generation. In this work, ultrathin cobalt sulfide nanosheets (Co3S4-NSs) on nickel foam (Ni-F) nanohybrids (termed as Co3S4-NSs/Ni-F) are synthesized using cyanogel hydrolysis and a sulfurization two-step approach. Physical characterizations reveal that Co3S4-NSs with a 1.7 nm thickness have abundant holes, implying the big surface area, abundant active edge atoms, and sufficient active sites. Electrochemical measurements show that as-synthesized Co3S4-NSs/Ni-F have excellent electrocatalytic activity and selectivity for ethanol oxidation reaction and hydrogen evolution reaction. Due to their bifunctional property of Co3S4-NSs/Ni-F nanohybrids, a symmetric Co3S4-NSs/Ni-F∥Co3S4-NSs/Ni-F ethanol electrolyzer can be effectively constructed, which only requires a 1.48 V electrolysis voltage to reach a current density of 10 mA cm-2 for high-purity hydrogen generation at the cathode as well as value-added potassium acetate generation at the anode, much lower than the electrolysis voltage of traditional electrochemical water splitting (1.64 V).

Activating the FeS (001) Surface for CO2 Adsorption and Reduction through the Formation of Sulfur Vacancies: A DFT-D3 Study

As a promising material for heterogeneous catalytic applications, layered iron (II) monosulfide (FeS) contains active edges and an inert basal (001) plane. Activating the basal (001) plane could improve the catalytic performance of the FeS material towards CO2 activation and reduction reactions. Herein, we report dispersion-corrected density functional theory (DFT-D3) calculations of the adsorption of CO2 and the elementary steps involved in its reduction through the reverse water-gas shift reaction on a defective FeS (001) surface containing sulfur vacancies. The exposed Fe sites resulting from the creation of sulfur vacancies are shown to act as highly active sites for CO2 activation and reduction. Based on the calculated adsorption energies, we show that the CO2 molecules will outcompete H2O and H2 molecules for the exposed active Fe sites if all three molecules are present on or near the surface. The CO2 molecule is found to weakly physisorb (−0.20 eV) compared to the sulfur-deficient (001) surface where it adsorbs much strongly, releasing adsorption energy of −1.78 and −1.83 eV at the defective FeS (001) surface containing a single and double sulfur vacancy, respectively. The CO2 molecule gained significant charge from the interacting surface Fe ions at the defective surface upon adsorption, which resulted in activation of the C–O bonds confirmed via vibrational frequency analyses. The reaction and activation energy barriers of the elementary steps involved in the CO2 hydrogenation reactions to form CO and H2O species are also unraveled.

Active facet determination of layered double hydroxide for oxygen evolution reaction

Correlation of edge area ratio and OER activity, cyanate inhibiting-probe and DFT calculation demonstrate that edge facet of LDHs is the real active facet in comparison with plane facet. Oxygen evolution reaction (OER) plays an indispensable role in developing renewable clean energy resources. One of the critical bottlenecks for the reaction is the development of highly efficient electrocatalyst to decrease the high overpotentials of four-electron transfer process of OER. Recently, layered double hydroxides (LDHs) have been widely investigated among the most promising electrocatalysts for OER due to their high intrinsic activity, excellent stability as well as low-cost. However, it remains unclear how the exposed facet of the LDHs affects their electrocatalytic activity. Here we elucidate the active edge facet of LDHs towards OER by combining the finely control of edge facet ratio coupled with molecular probe method and computational calculation. The LDHs with higher edge facet area ratio show superior activity with low onset potential as well as decreased Tafel slope. The active edge site is further proved by blocking the unsaturated edge sites with cyanate probe anion, of which the adsorption largely inhibits OER activity. Furthermore, based on density functional theory (DFT) calculation, two-dimensional map of theoretical overpotentials as a function of Gibbs free energy reveals that the edge (100) facet exhibits a much higher OER activity than basal plane (001) facet.

Boosting pH‐Universal Hydrogen Evolution of Molybdenum Disulfide Particles by Interfacial Engineering†

Main observation and conclusionThe design of high‐efficiency non‐noble and earth‐abundant electrocatalysts for hydrogen evolution reaction (HER) is highly paramount for water splitting and renewable energy systems. Molybdenum disulfide (MoS2) with abundant edge sites can be utilized as a promising alternative, but its catalytic activity is greatly related to the pH values, especially in an alkaline environment due to the extremely high energy barriers for water adsorption and dissociation steps. Here we report an exceptionally efficient and stable electrocatalyst to improve the sluggish HER process of layered MoS2 particles in different pH electrolytes, especially in base. The electrocatalyst is constructed by in situ growing selenium‐doped MoS2 (Se‐MoS2) nanoparticles on three‐dimensional cobalt nickel diselenide (Co0.2Ni0.8Se2) nanostructured arrays. Due to the large number of active edge sites of Se‐MoS2 particles exposed at the surface, robust electrical conductivity and large surface area of Co0.2Ni0.8Se2 support, and strong interfacial interactions between Se‐MoS2 and Co0.2Ni0.8Se2, this hybrid catalyst shows very outstanding catalytic HER properties featured by low overpotentials of 30 and 122 mV at 10 and 100 mA/cm2 with good operational stability in base, respectively, which outperforms most of inexpensive catalysts consisting of layered MoS2, transition metal selenides and sulfides, and it performs as well as noble Pt catalysts. Meanwhile, this electrocatalyst is also very active in neutral and acidic electrolytes, requiring low overpotentials of 93 and 94 mV at 10 mA/cm2, respectively, demonstrating its superb pH universality as a HER electrocatalyst with excellent catalytic durability. This study provides a straightforward strategy to construct an efficient non‐noble electrocatalyst for driving the HER kinetics in different electrolytes.