Liquid Electrode Research Articles

A sulphide resistant Ag|AgCl reference electrode for long-term monitoring.

Reference electrodes which demonstrate long-term potential stability are essential for many continuous monitoring applications and are commonly based on Ag|AgCl electrodes; however, these electrodes are susceptible to poisoning from aqueous sulphide species which are commonly present in wastewater and natural groundwater. This work presents a sulphide resistant solid-state reference electrode (SSRE) based on a composite material using suspended KCl electrolyte and sacrificial AgCl in a cross-linked polyvinyl acetate polymer matrix. Sulphidation of the sacrificial AgCl produces a stable Ag2S precipitate and prevents further ingress of the poisoning sulphide species through the composite material. A novel SSRE using this material is compared to a control SSRE without suspended AgCl and a typical liquid filled reference electrode. These three reference electrodes are studied using electrochemical impedance spectroscopy (EIS), and their application is also studied in potentiometric pH sensing and cyclic voltammetry (CV). The long-term sulphide resistance of the two SSREs is also studied with potentiometry, and cross-sections of these electrodes were examined using micro X-ray fluorescence (μXRF). Both SSREs demonstrated higher impedance than the liquid reference electrode but were similar to other SSREs reported in the literature. This impedance did not result a meaningful difference in potentiometric pH sensing or CV experiments done using typical scan rates. The KCl/AgCl SSRE exhibited remarkable sulphide resistance, with all samples demonstrating a stable potential without maintenance after ca. 120 days of continuous immersion in 1 g L-1 Na2S solution, whereas KCl SSRE samples all demonstrated significant drift before this time. μXRF sulphur maps revealed that suspended AgCl prevented sulphide ingress, thus protecting the embedded Ag|AgCl electrode. This work presents a reference electrode that could enable long-term monitoring in challenging sulphide solutions, and also highlights a novel approach for preventing reference electrode poisoning which could be more widely explored.

Experimental Study on a Glow Discharge Driven by a Flash Evaporation-Induced Density Gradient From Porous Conductive Liquid Electrodes

Experimental Study on a Glow Discharge Driven by a Flash Evaporation-Induced Density Gradient From Porous Conductive Liquid Electrodes

(Digital Presentation) Construction of a Novel Phosphate Potential Sensor and Its Application

Phosphorus content is one of important indicators in the evaluation of water quality. The level of phosphorus in oilfield water systems not only affects the overall water cycle production system, but excessive phosphorus wastewater entering the environment can cause eutrophication of the water body, as can high levels of ammonia and nitrogen, and leading to rapid growth of algae and thus affecting the balance of the aquatic ecosystem. Therefore, the regulation of phosphorus is of great importance. Phosphorus exists in nature mainly in the form of phosphate, which is currently detected by the traditional spectrophotometric method. As this method requires the addition of a large number of chemical reagents, it is not only complex and time consuming, but also produces a waste solution at the end of the test that can easily cause secondary pollution to the environment. Compared to traditional methods, Ion Selective Electrodes (ISEs) are easier to use, more sensitive, less expensive and do not cause secondary contamination. In conventional ion selective electrode detection systems, liquid contact ion selective electrodes consisting of a polymeric ion selective membrane, an internal filling fluid and an internal reference electrode are susceptible to common variables such as pressure and temperature. There are problems with complex maintenance, leakage and signal calibration. In contrast, all-solid ion-selective electrodes that eliminate the internal filling fluid and internal reference have become a hot research topic for such potential-based sensors. In this thesis, the following research was carried out with the aim of developing a phosphate potentiometric sensor with practical detection capabilities:(1) PANI/ITO electrodes were produced by electrodeposition of polyaniline on ITO conductive glass by constant potential deposition and by ultrasonic peeling. Three oxidation states of PANI/ITO electrodes were prepared at different voltages using phosphoric acid as the doping solution. LBPANI/ITO electrode in the fully reduced state, ESPANI/ITO electrode in the semi-oxidized state and PBPANI/ITO electrode in the fully oxidized state. The response sensitivity and stability of the three electrodes were investigated to determine the optimum doping potential; the response performance of the electrodes was tested for different doping times to determine the optimum preparation time. It is shown that the PBPANI/ITO electrode in the fully oxidized state has the optimum stability and response sensitivity at a doping time of 80 s. The electrode showed good linear response in the range of 1.00x10-5 ~ 1.00x10-1 M, with a response sensitivity of 37.30 dec/mV (R2 = 0.9966) and a detection limit of 10-5.6 M. The response time of the electrode to the solution was around 4 s, and it had good acid-base adaptability (pH 4.0 ~ 8.0). The performance of the prepared PBPANI/ITO electrode as a potentiometric phosphate sensor was also investigated in terms of stability (n = 10, RSD 1.76 %) and lifetime (6 weeks at room temperature), and was successfully used for phosphate detection and analysis in oilfield re-injection water, lake water and tap water samples in real environments with satisfactory results. (2) To further prepare a phosphate potential sensor with a high sensitivity response. We pretreated the home-made cobalt electrode with high pressure anodic oxidation in sodium hydroxide solution to produce a uniform cobalt oxide passivation film on the electrode surface. The sensitivity and stability of the response of the electrode at different pretreatment times were investigated to determine the optimum preparation conditions. The results showed that the pretreated cobalt electrode had a good response in the range of 1.00x10-5 ~ 1.00x10-1 M. The response sensitivity was 67.22 mV dec, R2 = 0.9939 and the detection limit was 10-5.5 M. It was much higher than that of the untreated cobalt electrode. This far exceeded that of the untreated polished cobalt electrode (36 ~ 40 mV/dec). The performance of the pretreated cobalt electrode as a potentiometric phosphate sensor was also investigated in terms of lifetime (7 weeks at room temperature), response rate (less 40 s), stability (n = 10, RSD 1.07 %) and acid-base adaptability (pH 4.0 ~ 8.0), and the sensor was successfully used for phosphate in oilfield re-injection water, lake water and tap water samples with satisfactory results.

Carbon Dioxide Reduction on Alloyed Galinstan

Solar powered electrochemical CO₂ reduction to disposable products is presently being developed as one of negative carbon emission technologies1. State-of-the-art electrocatalysts are mainly developed for the CO2 reduction to hydrogen rich products or chemical feedstock materials while for the above-mentioned application solid carbon-rich products are desired (best pure carbon). Even though the formation of solid products is sometimes observed on catalysts (coking effect), this usually leads to an undesirable irreversible deactivation of their solid interfaces.Thus, the development of next generation CO2 electrocatalysts is demanded based on liquid metal alloys such as galinstan (GaInSn). The advantage of using liquid phase electrodes is to eliminate coking and coarsening limitations that are associated with solid catalysts. For example, it has been reported that ceria-supported liquid galinstan can electrochemically produce carbonaceous materials from CO2 gas2. This shows, that doping with additional active elements can change the CO2 reduction activity of GaInSn in the direction of other desired products.Our work investigates the activity of galinstan for the electroreduction of CO2 depending on alloying with additional metals (such as Ce, Ag, Pb). While pure GaInSn shows a predominant activity for the formation of C1 products (CO, HCOOH) in DMF/H2O electrolyte, we are mainly interested in the formation of solid carbon or oxalate. Therefore, our investigations aim at finding suitable modifications of GaInSn that achieve high selectivity for these products. Electrochemical analysis coupled with in-line gas chromatography and in-line mass spectroscopy are used to characterize the reactivity. Furthermore, the influence of the water content of the organic electrolyte on the product selectivity will be investigated. In particular, to suppress the observed low hydrogen evolution as a by-product even more efficiently. May, M. M.; Rehfeld, K., Negative Emissions as the New Frontier of Photoelectrochemical CO2 Reduction. Advanced Energy Materials 2022, 2103801.Esrafilzadeh, D.; Zavabeti, A.; Jalili, R.; Atkin, P.; Choi, J.; Carey, B. J.; Brkljača, R.; O’Mullane, A. P.; Dickey, M. D.; Officer, D. L.; MacFarlane, D. R.; Daeneke, T.; Kalantar-Zadeh, K., Room Temperature CO2 Reduction to Solid Carbon Species on Liquid Metals Featuring Atomically Thin Ceria Interfaces. Nature Communications 2019, 10 (1), 865. Figure 1

Electrolyte Flow through Porous Carbon Electrodes Under Compression in the Hydrogen-Bromine Redox Flow Battery

The conditions of electrolyte flow affect the performance of redox flow batteries through the combined effect of pumping energy and electrode overpotential. In the hybrid hydrogen-bromine flow battery the conditions of electrolyte flow depend on the trans-membrane pressure exerted by hydrogen gas in the membrane electrode assembly, which has a compressive effect on the liquid side electrode.This study aims at characterizing the effect of hydrogen pressure on flow characteristics and investigate its effect on transport behavior. We selected two types of porous carbon electrodes, carbon paper and carbon cloth, with and without surface conditioning, and study liquid flow at the compression ratios expected in a hydrogen-bromine cell under increasing operation pressure.Combination of electrode characterization with electrolyte velocity measurements obtained by particle image velocimetry in flow-through configuration allow characterization of liquid flow through porous electrodes, and attempt to relate it to electrode morphology. Electrochemical testing is then is used to reveal the effect of electrode compression on electrochemical active surface area, estimated by the capacitance of the double layer, and cell polarization.The velocity field is revealed to be highly dependent on the fiber structure of the electrode and surface conditioning. The effect of compression manifests early and impacts the uniformity of flow through the porous structure. Additionally, the changes in active area and cell resistance result in a complex combination of factors that determine cell polarization. Figure 1

Role of Chemisorbing Species in Growth at Liquid Metal-Electrolyte Interfaces Revealed by in Situ X-Ray Scattering

Liquid-liquid interfaces offer intriguing possibilities for nanomaterials growth. Especially, growth at liquid metal surfaces has recently received renewed interest. Here, fundamental interface-related mechanisms that control the growth behavior in these systems are studied for the case of Pb halide compound formation at the interface between liquid mercury electrode and aqueous salt solutions, using in situ X-ray reflectivity and grazing incidence X-ray diffraction, supplemented by electrochemical measurements and optical microscopy. The nucleation and growth of these compounds at potentials in the regime of Pb de-amalgamation was investigated in NaX + PbX2 (X = F, Cl, Br) to systematically explore the role of the halide species. X-ray reflectivity studies reveal the rapid formation of well-defined ultrathin precursor adlayers in Cl- and Br-containing solution. This adlayer formation is followed by subsequent quasi-epitaxial growth of Pb(OH)X bulk crystals, that are oriented with the c-axis along the surface normal. In contrast, growth in F-containing solution proceeds by slow formation of a more disordered deposit, resulting in random bulk crystal orientations on the Hg surface. A detailed structural analysis of the Pb(OH)Br and Pb(OH)Cl precursor adlayers reveals that they determine the orientation of the subsequently formed bulk crystals, with the arrangement in the adlayer providing a template. Together with our previous results on the pseudo-epitaxial growth of PbFBr on Hg (A. Elsen, et al., Proc.Nat.Acad.Sci., 2013, 110, 6663), these data reveal the decisive role of the interface chemistry, especially the strong chemisorption of the anions bromide and chloride, in steering the formation of these textured deposits at the liquid metal surface.

Activation Energies of Heterogeneous Electrocatalysis: A Theoretical Perspective.

Heterogeneous electrochemistry is important for various applications. However, currently, there is limited information about activation energies. In this invited review, we review the challenges associated with calculating these activation energies. Specifically, we highlight three key difficulties in atomistic modeling: liquid structure, electrode potential, and electrolyte ions, along with state-of-the-art methods to address them. We aim to inspire more studies in the field of activation energies to better understand and design heterogeneous electrocatalysts.

Ultrahigh-gain organic transistors based on van der Waals metal-barrier interlayer-semiconductor junction.

Intrinsic gain is a vital figure of merit in transistors, closely related to signal amplification, operation voltage, power consumption, and circuit simplification. However, organic thin-film transistors (OTFTs) targeted at high gain have suffered from challenges such as narrow subthreshold operating voltage, low-quality interface, and uncontrollable barrier. Here, we report a van der Waals metal-barrier interlayer-semiconductor junction-based OTFT, which shows ultrahigh performance including ultrahigh gain of ~104, low saturation voltage, negligible hysteresis, and good stability. The high-quality van der Waals-contacted junctions are mainly attributed to patterning EGaIn liquid metal electrodes by low-energy microfluidic processes. The wide-bandgap semiconductor Ga2O3 as barrier interlayer is achieved by in situ surface oxidation of EGaIn electrodes, allowing for an adjustable barrier height and expected thermionic emission properties. The organic inverters with a high gain of 5130 and a simplified current stabilizer are further demonstrated, paving a way for high-gain and low-power organic electronics.

Serpentine liquid electrode based Dual-mode skin Sensors: Monitoring biomechanical movements by resistive or triboelectric mode

Flexible and stretchable electrodes are crucial components for wearable electronic devices. Herein, a serpentine liquid electrode based dual-mode skin sensors (SLEDSS) that leverages a highly deformable and serpentine liquid electrode is developed. The functional carboxylated multi-walled carbon nanotubes / Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (MWCNT-COOH / PEDOT: PSS) network structure endows the SLEDSS with a stable linear change in resistance. Additionally, a solid–liquid double electric layer generated between the solid surface and liquid electrode facilitates a higher triboelectric output performance. As a result, the SLEDSS features dual-modal sensing capabilities, including both resistive and triboelectric modes. The flowability of the liquid electrode enables it to fully adapt to different types of deformation, thereby allowing SLEDSS to effectively collect energy in different forms of movement, such as tapping, stretching, bending, twisting, and unpredictable transformations based on practical applications. SLEDSS can maintain its performance even at up to 550.32% strain, displaying a monotonically increasing relationship between the stretchable length and open-circuit voltage. Finally, the SLEDSS is applied as a wearable power source and self-powered sensor for monitoring biomechanical movements, the excellent stretchable performance and ultra-high sensitivity to mechanical stimulation provided by the SLEDSS offer new prospects for self-powered sensors.

Electrosynthesis of Quasi-Epitaxial Crystals on Liquid Metals.

Electrosynthesis of single-crystalline metallic and intermetallic particles with a preferred orientation onto liquid metal electrodes has been performed. Liquid gallium electrodes immersed in aqueous alkaline electrolytes without any molecular additive or external solid seeding substrates were used to electroreduce separately Pb2+, Bi3+, Pd2+, and Mn2+. The crystallinity, composition, and orientation of the electrodeposition products were characterized by using scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, grazing incidence X-ray diffraction, and energy-dispersive X-ray spectroscopy. Electrodeposition of Pb and Bi results in the incipient formation of two-dimensional (2D) nuclei that subsequently direct the growth of Pb and Bi single crystals along the most close-packed [111] and [0001] directions, respectively. The absence of any intervening surface oxides and a low electroreduction flux are necessary to avoid polycrystalline dendrite formation. Under comparable conditions, the electrodeposition of Pd and Mn results in single-crystalline intermetallic particles at the interface. Each crystal exhibits a preferred orientation consistent with the unique atomic packing of the near-surface region of the liquid Ga. The presented study suggests a new concept in electrodeposition processes where the liquid metal structure imparts quasi-epitaxial growth in a system in which the electrode material specifically has no crystallinity or long-range order. This study is thus the first demonstration of highly oriented electrodeposition at a liquid/liquid interface under ambient conditions, highlighting the unique solvation environment of liquid metal interfaces for forming thin metallic and intermetallic films.

New Ion Selective Electrodes for Analysis of Metformin Based on Molecularly Imprinted Polymers

Metformin (MEF) imprinted polymer liquid electrodes arecreated using a precipitation polymerization process. The MEF served as a template for the creation of molecularly imprinted (MIP) materials using benzoyl peroxide (BPO) as an initiator, allyl methacrylate (AMA) crosslinkers, and glycidyl methacrylate (GMA) as a monomer. UtilizingDi-octyl-phthalate (DOPH) and di-butyl phthalate (DBPH) as plasticizers in a PVC matrix, the molecularly imprinted membranes arecreated. The reaction time is approximately 50 seconds, and the limits of detection for liquid electrodes, as determined by the calibration curves, are 55.6 to 58.4 mV/decadeat 5×10-5M and 8×10-5M respectively. The liquid electrodes demonstrated good selectivity over a variety of species and a consistent reaction when filled with a typical 0.1 M drug solution across the pH range of 1 to 11. Modern electrodes can detect MEF without the need for time-consuming pre-treatment procedures in pharmaceutical samples.

Continuous desalination and high-density energy storage: Na metal hybrid redox flow desalination battery

Redox flow desalination batteries (RFDBs) provide sustainable and energy-efficient solutions for simultaneously resolving energy storage and desalination challenges. However, harnessing these bifunctional batteries is plagued by two major issues: 1. Liquid redox electrodes cause low energy density (<329 Ah/L), increasing system volume. 2. Intermittent desalination during charge or discharge phases hampers overall productivity. Our study introduces a novel configuration, replacing the liquid electrode with sodium metal, substantially increasing the energy density (1128 Ah/L). We also implement continuous desalination by interlaying alternating cation and anion exchange membranes between electrodes. Benefiting from the high energy density battery capable of continuous desalination, it demonstrates 95 % ion removal by treating natural seawater throughout the cyclic operation while consuming 1.40 min Wh/molNaCl (competitive with the conventional seawater reverse osmosis technology (4.06 Wh/molNaCl)). Our work is a critical step towards the practical adoption of desalination batteries, enhancing energy and environmental sustainability.

Hyphenated liquid electrode glow discharge-dielectric barrier discharge molecular emission spectrometry for determination of dithiocarbamates.

A hyphenated liquid electrode glow discharge (LEGD)-dielectric barrier discharge (DBD) molecular emission spectrometer was constructed and used as a novel liquid chromatography (LC) detector for dithiocarbamates (DTC) determination. The LEGD was used as an acidolysis reactor for the in-situ transformation of DTCs into CS2 with high efficiencies of 74.11-97.98%. The DBD was used to excite CS2 gas to generate a specific molecular emission at 257.94nm. The linear correlation coefficient of the method was>0.99 from 1 to 200μgmL-1. The detection limits ranged from 0.1 to 0.3μgmL-1 with 76-119% recovery and relative standard deviations of 0.2-8.5%. Moreover, the hyphenated microplasma spectrometer achieved low power consumption, low temperature, immediate acidolysis, and high transformational efficiency, and can detect each DTC when combined with LC.

Fast chromium determination in pharmaceutical tablets by using electrochemical sensors: Preparation and comparison

In the present paper, three electrodes were prepared with the aim of detecting chromium (III) in pharmaceutical tablets and comparing their capabilities and efficiency. At first, N-(pyridine-2-ylcarbamothioyl) benzamide (NP2YCTB) was synthesized and characterized by 1H NMR, FTIR, and 13C NMR spectroscopy methods. Then, it is used as a sensing material to prepare three types of chromium potentiometry sensors including solid-state electrodes (SSE), coated wire electrodes (CWE) as asymmetric electrodes, and liquid membrane electrodes (LME) as symmetric electrodes. The responses of all electrodes were Nernstian. Field-emission scanning electron microscopy was utilized to investigate the liquid membrane morphology. The presence of chromium (III) in the membrane was proved using Energy-dispersive X-ray spectroscopy and the coordination of NP2YCTB heteroatoms with chromium (III) was confirmed by Fourier transform infrared spectroscopy. The limit of detection for SSE (3 × 10−9 mol/L) was enhanced compared with LME (7 × 10−6 mol/L) and CWE (3 × 10−7 mol/L). The response time of electrodes was very short so it was about 5–6 s for LME and CWE and 5–8 s for SSE. The sensors were used for the potentiometric determination of chromium (III) in pharmaceutical tablets and in the potentiometric titration of it with EDTA.

Multi-functional single cell manipulation method based on a multichannel micropipette

Cell manipulation techniques that provide versatility in handling various cell types and performing diverse manipulations are essential for advancing biological research. This study presents a novel and adaptable approach utilizing a multifunctional micropipette for precise single-cell operations, including three-dimensional (3D) manipulation, trapping, lysis, and aspiration. The multifunctional micropipette comprises two liquid metal-based channels with high electrical conductivity, along with a negative pressure-based aspiration channel. By utilizing the liquid metal electrodes, the system enables the application of electrical stimulation, inducing both dielectrophoretic force and electroporation on cells. Through the implementation of dielectrophoretic force and integration with a 3D-movable stage, single cells can be patterned, manipulated in 3D, accurately trapped, and separated with a minimal adjacent distance of 10 µm. By utilizing the electroporation phenomenon, rapid lysis of suspension cells can be achieved within 50 ms, while adherent cells can be lysed within 200 ms, utilizing a square-wave electrical signal with a frequency of 1 kHz and an amplitude of 40 Vpp. Furthermore, the study explores the impact of electrode size on the lysis of adherent cell groups. Additionally, the utilization of negative pressure for lysate aspiration is also demonstrated. In summary, the reported technique is versatile for single cell manipulation.

Flexible Finely and Directly Patternable Liquid Metal Electrodes via Selective Surface Wetting Technique

Eutectic gallium–indium (EGaIn) is an ideal material for preparing flexible electrodes, but its high surface tension poses a challenge during deposition and patterning. Herein, we propose a laser-induced selective surface wetting technique (SSWT) to enable the facile and straightforward fabrication of flexible finely and directly patternable EGaIn liquid metal electrodes. Our proposed technique selectively controls the wettability of EGaIn by establishing a perfluorinated self-assembled monolayer on a zinc oxide nanorod array to impart superhydrophobicity and then inducing specific sites on the hydrophilized surface by ultraviolet (UV) pulsed laser ablation, thereby enabling fine patterning (linewidth, ~50 μm). Surface analysis of the effect of laser ablation was also performed to elucidate the mechanism of SSWT. The patterned EGaIn liquid metal electrode fabricated by SSWT exhibited superior flexibility, with a resistance change (ΔR/R0) of only 18.6% compared with a Ag thin film electrode, which showed a dramatic increase in ΔR/R0 to nearly 500% after 50,000 folding cycles at a peak strain of 2.5%. The simple and easily implementable liquid metal patterning technique proposed in this study may potentially be applied in the field of wearable and stretchable electronics, which requires extreme flexibility.

Application of liquid Ga-Pb cathode for selective separation of samarium fission products from molten alkali metal chlorides

The efficient separation of the rare earth element Sm from spent nuclear fuel is of strategic importance for the nuclear industries. This study explored the feasibility of a novel liquid Ga-Pb hybrid electrode for electrochemical extraction of samarium compounds, and the electrochemical reduction mechanism and dynamic properties of Sm(III) ions were provided in NaCl-2CsCl molten salt. It was established that the reduction mechanisms of Sm(III) to Sm(II) and Pb(II) to Pb(0) on the Mo cathode were a one-step reaction processes, respectively, while Ga(III) to Ga(0) was a two-step reaction process. The co-deposition mechanisms of Sm(III), Ga(III) and Pb(II) ions on the Mo cathode were identified, and the types of intermetallic compounds, formation potentials and reaction processes were analyzed. The deposition potential of Sm on Ga-Pb mixed cathode is determined, and the value of its depolarization was greater than on the liquid Pb electrode. Simultaneously, Sm ions have higher exchange current densities and lower activation energies for electrode reactions on the liquid Ga-Pb mixed electrodes than on the liquid Pb electrodes. Furthermore, the electro-separation of NaCl-2CsCl-SmCl3 molten salt was executed via potentiostatic electrolysis technique, and the separation efficiency and the effect of cathode product type were analyzed and compared in Ga-Pb hybrid electrode and Pb electrode. It was obtained that the maximum extraction efficiency on the Ga-Pb hybrid electrode and the separation efficiency of Sm could reach 91.3 % after 8 h of electrolysis.

Silky Liquid Metal Electrodes for On-Skin Health Monitoring.

Next generation on-skin electrodes will require soft, flexible, and gentle materials to provide both high-fidelity sensing and wearer comfort. However, many commercially available on-skin electrodes lack these key properties due to their use of rigid hardware, harsh adhesives, uncomfortable support structures, and poor breathability. To address these challenges, this work presents a new device paradigm by joining biocompatible electrospun spider silk with printable liquid metal to yield an incredibly soft and scalable on-skin electrode that is strain-tolerant, conformable, and gentle on-skin. These electrodes, termed silky liquid metal (SLiM) electrodes, are found to be over five times more breathable than commercial wet electrodes, while the silk's intrinsic adhesion mechanism allows SLiM electrodes to avoid the use of harsh artificial adhesives, potentially decreasing skin irritation and inflammation over long-term use. Finally, the SLiM electrodes provide comparable impedances to traditional wet and other liquid metal electrodes, offering a high-fidelity sensing alternative with increased wearer comfort. Human subject testing confirmed the SLiM electrodes ability to sense electrophysiological signals with high fidelity and minimal irritation to the skin. The unique properties of the reported SLiM electrodes offer a comfortable electrophysiological sensing solution especially for patients with pre-existing skin conditions or surface wounds.

Nanofluids and Ionic Fluids as Liquid Electrodes: An Overview on Their Properties and Potential Applications

The current review work focuses on recent developments in the exploration of electroactive nanofluids, ionanofluids, and ionic liquids acting as liquid electrodes. The nanofluids used for this purpose are composed of organic or aqueous electrolytes as base fluids with the addition of nanoparticles in pure, oxidized, or hybrid forms. On the other hand, the ionic liquids are formed by adding a solution, which can be an acid, a base, or a salt, in water. The electrochemical properties, such as electrical conductivity and capacitance, of these innovative fluids are discussed thoroughly, along with their influencing factors, such as the nature and concentration of the included nanoparticles, the type of base fluids, and the operating temperature. Moreover, this overview summarizes the fundamental applications of electroactive nanofluids, ionanofluids, and ionic liquids in various possible flow-cell configurations and electrolysis methods, along with the associated feasibility factors. Additionally, this survey of scientific papers on the matter enabled the listing and evaluation of general aspects related to the usage of electroactive nanofluids, ionanofluids, and ionic liquids. Finally, it addresses the main problems associated with such types of fluids and outlines the primary prospects for further research and utilization of electroactive nanofluids, ionanofluids, and ionic liquids in diverse scientific and technological fields.

Triboelectric nanogenerator based on a water droplet spring with a concave spherical surface for harvesting wave energy and detecting pressure

Abstract Triboelectric nanogenerator (TENG) has strong application potential in collecting nano energy and detecting micro motion. In this study, a TENG based on a water droplet spring with a concave spherical surface was proposed. The dispersive-aggregative triboelectric nanogenerator (DA-TENG) added the water droplet to the concave spherical surface which was covered with circular copper foil electrode and polytetrafluoroethylene. External loading/unloading caused water droplet dispersion/aggregation. Therefore, the solid and liquid electrodes could generate voltage by contacting and separating. Meanwhile, DA-TENG design parameters were optimized to find optimal output conditions, including the water droplet volume, the cross-sectional radius of the concave spherical surface, the force area of the elastic membrane, and the excitation frequency of the shaker. In addition, the voltage signal generated by volunteers pressing DA-TENG could show the keyboard usage habits of different people and thus serve as a basis for personnel identification, which suggested DA-TENG could be used as a self-powered pressure detector. Finally, DA-TENG was designed as a harvesting wave energy device. Under a 6 MΩ load, a unit of work could produce a peak current of 1.7 μA and an effective power of 8.82 μW; three units could produce a peak current of 5.3 μA.