Electrode Size Research Articles

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.

Fabrication and Evaluation of Embroidery-Based Electrode for EMG Smart Wear Using Moss Stitch Technique

Wearable 2.0 research has been conducted on the manufacture of smart fitness wear that collects bio-signals through the wearing of a textile-based electrode. Among them, the electromyography (EMG) suit measures the electrical signals generated by the muscles to check their activity, such as contraction and relaxation. General gel-type electrodes have been reported to cause skin diseases due to an uncomfortable feel and skin irritation when attached to the skin for a long time. Dry electrodes of various materials are being developed to solve this problem. Previous research has reported EMG detectio performance and conducted economic comparisons according to the size and shape of the embroidery electrode. On the other hand, these embroidery electrodes still have foreign body sensations. In this study, a moss sEMG electrode was produced with various shapes (W3 and WF) and loop lengths (1–5 mm). The optimized conditions of the embroidery-based electrodes were derived and analyzed with the tactile comfort factors and sensing performances. As the loop length of the electrode increased, MIU and Qmax increased, but the SMD decreased due to the free movement of the threads constituting the loop. Impedance and sEMG detection performance showed different trends depending on the electrode type.

Effects of multisession cathodal transcranial direct current stimulation with cognitive training on sociocognitive functioning and brain dynamics in autism: A double-blind, sham-controlled, randomized EEG study

BackgroundFew treatment options are available for targeting core symptoms of autism spectrum disorder (ASD). The development of treatments that target common neural circuit dysfunctions caused by known genetic defects, namely, disruption of the excitation/inhibition (E/I) balance, is promising. Transcranial direct current stimulation (tDCS) is capable of modulating the E/I balance in healthy individuals, yet its clinical and neurobiological effects in ASD remain elusive. ObjectiveThis double-blind, randomized, sham-controlled trial investigated the effects of multisession cathodal prefrontal tDCS coupled with online cognitive remediation on social functioning, information processing efficiency and the E/I balance in ASD patients aged 14–21 years. MethodsSixty individuals were randomly assigned to receive either active or sham tDCS (10 sessions in total, 20 min/session, stimulation intensity: 1.5 mA, cathode: F3, anode: Fp2, size of electrodes: 25 cm2) combined with 20 min of online cognitive remediation. Social functioning, information processing efficiency during cognitive tasks, and theta- and gamma-band E/I balance were measured one day before and after the treatment. ResultsCompared to sham tDCS, active cathodal tDCS was effective in enhancing overall social functioning [F(1, 58) = 6.79, p = .012, ηp2 = 0.105, 90% CI: (0.013, 0.234)] and information processing efficiency during cognitive tasks [F(1, 58) = 10.07, p = .002, ηp2 = 0.148, 90% CI: (0.034, 0.284)] in these individuals. Electroencephalography data showed that this cathodal tDCS protocol was effective in reducing the theta-band E/I ratio of the cortical midline structures [F(1, 58) = 4.65, p = .035, ηp2 = 0.074, 90% CI: (0.010, 0.150)] and that this reduction significantly predicted information processing efficiency enhancement (b = −2.546, 95% BCa CI: [-4.979, −0.113], p = .041). ConclusionOur results support the use of multisession cathodal tDCS over the left dorsolateral prefrontal cortex combined with online cognitive remediation for reducing the elevated theta-band E/I ratio in sociocognitive information processing circuits in ASD patients, resulting in more adaptive regulation of global brain dynamics that is associated with enhanced information processing efficiency after the intervention.

Determining the corticospinal, intracortical and motor function responses to transcranial alternating current stimulation of the motor cortex in healthy adults: A systematic review and meta-analysis

BackgroundTranscranial Alternating Current Stimulation (tACS) employs low-intensity sinusoidal currents to influence cortical plasticity and motor function. Despite extensive research, inconsistent results require a comprehensive review of tACS efficacy. ObjectiveThis study systematically assesses tACS effects on corticospinal and intracortical excitability, and motor function over the motor cortex (M1), focusing on alpha, beta, and gamma frequencies. MethodsRelevant studies were identified through database searches and citations were tracked until July 10, 2023. The methodological quality of the included studies (29) was evaluated by Downs and Black. Data synthesis involved meta-analysis (n = 25) and best evidence synthesis (n = 5). ResultsMeta-analysis revealed that alpha and beta tACS with intensities > 1 mA and tACS with individualised alpha frequency (IAF) increased corticospinal excitability (CSE). tACS over M1 improved motor function, irrespective of stimulation frequency and intensity. Sub-analysis showed that alpha and beta tACS with an intensity ≤ 1 mA led to improved motor function, while gamma tACS at 2 mA enhanced motor function. Additionally, beta tACS at a fixed frequency of 20 Hz, as well as both low gamma (30–55) and high gamma (55–80) tACS, resulted in improved motor function. A stimulation duration of 20 min led to improvements in both CSE and motor function, and tACS with electrode sizes smaller than 35 cm2 and an electrode montage over M1-supraorbital region (SOR) were found to enhance motor function. Notably, both online and offline tACS improved motor function, regardless of stimulation factors. ConclusiontACS modulates CSE and improves motor function, with outcomes dependent on stimulation parameters and timing.

Understanding the Impact of Active-to-Passive Area Ratio on Deformation in One-Dimensional Dielectric Elastomer Actuators with Uniaxial Strain State.

There is increasing interest in the use of novel elastomers with inherent or modified advanced dielectric and mechanical properties, as components of dielectric elastomer actuators (DEA). This requires corresponding techniques to assess their electro-mechanical performance. A common way to test dielectric materials is the fabrication of actuators with pre-stretch fixed by a stiff frame. This results in the problem that the electrode size has an influence on the achievable actuator displacement and strain, which is detrimental to the comparability of experiments. This paper presents an in-depth study of the active-to-passive ratio with the aim of investigating the influence of the coverage ratio on uniaxial actuator displacement and strain. To model the effect, a simple lumped-parameter model is proposed. The model shows that the coverage ratio for maximal displacement is 50%. To validate the model results, experiments are carried out. For this, a rectangular, fiber-reinforced DEA is used to assess the relation of the coverage ratio and deformation. Due to the stiffness of the fibers, highly anisotropic mechanical properties are achieved, leading to the uniaxial strain behavior of the actuator, which allows the validation of the one-dimensional model. To consider the influence of the simplifications in the lumped-parameter model, the results are compared to a hyperelastic model. In summary, it is shown that the ratio of the active-to-passive area has a significant influence on the actuator deformation. Both the model and experiments confirm that an active-to-passive ratio of 50% is particularly advantageous in most cases.

Application of facial neuromuscular electrical stimulation (fNMES) in psychophysiological research: Practical recommendations based on a systematic review of the literature

Facial neuromuscular electrical stimulation (fNMES), which allows for the non-invasive and physiologically sound activation of facial muscles, has great potential for investigating fundamental questions in psychology and neuroscience, such as the role of proprioceptive facial feedback in emotion induction and emotion recognition, and may serve for clinical applications, such as alleviating symptoms of depression. However, despite illustrious origins in the 19th-century work of Duchenne de Boulogne, the practical application of fNMES remains largely unknown to today’s researchers in psychology. In addition, published studies vary dramatically in the stimulation parameters used, such as stimulation frequency, amplitude, duration, and electrode size, and in the way they reported them. Because fNMES parameters impact the comfort and safety of volunteers, as well as its physiological (and psychological) effects, it is of paramount importance to establish recommendations of good practice and to ensure studies can be better compared and integrated. Here, we provide an introduction to fNMES, systematically review the existing literature focusing on the stimulation parameters used, and offer recommendations on how to safely and reliably deliver fNMES and on how to report the fNMES parameters to allow better cross-study comparison. In addition, we provide a free webpage, to easily visualise fNMES parameters and verify their safety based on current density. As an example of a potential application, we focus on the use of fNMES for the investigation of the facial feedback hypothesis.

Unleashing the potential of morphotropic phase boundary based hybrid triboelectric–piezoelectric nanogenerator

Morphotropic phase boundary (MPB)-based ceramics are excellent for energy harvesting due to their enhanced physical properties at phase boundaries, broad operating temperature range, and ability to customize properties for efficient conversion of mechanical energy into electrical energy. In this work, Bi1–xNaxFe1–xNbxO3 (x = 0.20, 0.30, 0.32 and 0.40, BNFNO abbreviation) based ceramics were synthesized using a solid-state route and blended with Polydimethylsiloxane (PDMS) to achieve flexible composites. Various material characterization and energy harvesting were performed by designing a hybrid piezoelectric (PENG)-triboelectric (TENG) device. The voltage and current of PENG, TENG, and hybrid bearing same device area (2 cm × 2 cm) were recorded as 11 V/0.3 μA; 60 V/0.7 μA; 110 V/2.2 μA. The strategies for enhancing the output performance of the hybrid device were evaluated, such as increased surface area (creating micro-roughness and porous morphology) and increasing electrode size and multi-layer hybrid device formation. The self-powered acceleration monitoring was demonstrated using the hybrid device. Further, the low-frequency-based wave energy is converted into electrical energy, confirming the usage of hybrid PENG-TENG devices as a base for battery-free sensors and blue energy harvesting.

Finding Balance with Vestibular Stimulation

Weakening of the vestibular system through disease or aging leads to imbalance, restricted mobility, and falls (Hain et al., 2018). Vestibular weakness affects one-third of people over the age of 40, and 85% of those over 80 years (Agrawal et al., 2009). The delicate cells of the vestibular system do not regenerate and thus it becomes an incurable chronic condition. A promising treatment is noisy galvanic vestibular stimulation (nGVS), a non-invasive electrical stimulation, delivered to the vestibular system, aiming to restore absent vestibular information and improve balance (McLaren et al., 2022). This presentation reports the results of a scoping review investigating the stimulation parameters that can be manipulated to improve the efficacy of nGVS. A comprehensive systematic search of five databases up to December 2022 identified studies applying nGVS to people with the aim of improving their postural control. Two independent reviewers screened and identified eligible studies and extracted parameter data. Thirty-one studies met the eligibility criteria. The review identified that a broad array of settings have been employed across studies. The nGVS parameters of waveform, amplitude, frequency band, duration of stimulation, method of amplitude optimization, size and composition of electrodes and the electrode skin interface are all likely to influence the efficacy of nGVS. However, the ability to draw robust conclusions about the selection of optimal nGVS parameters is hindered by a lack of studies that directly compare parameter settings. I propose a guideline for the accurate reporting of nGVS parameters. This will help establish standardized stimulation protocols bringing us one step closer to becoming a readily available clinical treatment.

Hierarchical Morphing Control of an Ultra-Lightweight Electro-Actuated Polymer Telescope with Thin-Film Actuators.

This paper explores advanced shape control techniques for ultra-lightweight electro-actuated polymers with composite ferroelectric thin films. It begins with an overview of PVDF-TrFE film actuators used in the development of thin-shell composites, emphasizing the need to overcome constraints related to the electrode size for successful scalability. Strain generation in thin-film actuators is investigated, including conventional electrode-based methods and non-contact electron flux excitation. Numerical studies incorporate experimentally calibrated ferroelectric parameters, modeling non-contact actuation with an equivalent circuit representation. The potential distribution generated by electron flux injection highlights its potential for reducing print-through actuation issues. Additionally, the paper outlines a vision for the future of large thin-shell reflectors by integrating the discussed methods for charging ferroelectric polymer films. A hierarchical control strategy is proposed, combining macro- and micro-scale techniques to rectify shape errors in lightweight reflectors. These strategies offer the potential to enhance precision and performance in future spaceborne observation systems, benefiting space exploration and communication technologies.

Boosting the Lithium Storage Properties of a Flexible Li4Ti5O12/Graphene Fiber Anode via a 3D Printing Assembly Strategy

Traditional lithium-ion batteries cannot meet the high flexibility and bendability requirements of modern flexible electronic devices due to the limitations of the electrode material. Therefore, the development of high-performance flexible energy storage devices is of great significance for promoting flexible electronics. In recent years, one-dimensional flexible fiber lithium-ion batteries have been rapidly developed due to their advantages of high flexibility and bendability. However, it remains highly challenging to realize 1D flexible fiber lithium-ion batteries with excellent electrochemical properties and good mechanical performance. In this work, a reduced graphene oxide-based printing ink is proposed for the fabrication of flexible Li4Ti5O12/graphene fiber electrodes using a 3D printing assembly strategy. It is noteworthy that the green reducing agent vitamin C was used to reduce the graphene oxide in one step, which improved the conductivity of the fiber electrode. Furthermore, a 3D conductive network was constructed inside the fiber electrodes due to the high specific surface area of the reduced graphene oxide, which enhanced the electronic conductivity and ion mobility. The fiber electrode not only exhibits good mechanical performance, but also has excellent electrochemical properties. Equally importantly, the method is simple and efficient, and the working environment is flexible. It can precisely control the shape, size and structure of the one-dimensional fiber flexible electrode, which is of great significance for the development of future flexible electronic devices.

Integrating electric field modeling and pre-tDCS behavioral performance to predict the individual tDCS effect on visual crowding

Objective. Transcranial direct current stimulation (tDCS) has been broadly used to modulate brain activity with both bipolar and high-definition montages. However, tDCS effects can be highly variable. In this work, we investigated whether the variability in the tDCS effects could be predicted by integrating individualized electric field modeling and individual pre-tDCS behavioral performance. Approach. Here, we first compared the effects of bipolar tDCS and 4 × 1 high-definition tDCS (HD-tDCS) with respect to the alleviation of visual crowding, which is the inability to identify targets in the presence of nearby flankers and considered to be an essential bottleneck of object recognition and visual awareness. We instructed subjects to perform an orientation discrimination task with both isolated and crowded targets in the periphery and measured their orientation discrimination thresholds before and after receiving 20 min of bipolar tDCS, 4 × 1 HD-tDCS, or sham stimulation over the visual cortex. Individual anatomically realistic head models were constructed to simulate tDCS-induced electric field distributions and quantify tDCS focality. Finally, a multiple linear regression model that used pre-tDCS behavioral performance and tDCS focality as factors was used to predict post-tDCS behavioral performance. Main results. We found that HD-tDCS, but not bipolar tDCS, could significantly alleviate visual crowding. Moreover, the variability in the tDCS effect could be reliably predicted by subjects’ pre-tDCS behavioral performance and tDCS focality. This prediction model also performed well when generalized to other two tDCS protocols with a different electrode size or a different stimulation intensity. Significance. Our study links the variability in the tDCS-induced electric field and the pre-tDCS behavioral performance in a visual crowding task to the variability in post-tDCS performance. It provides a new approach to predicting individual tDCS effects and highlights the importance of understanding the factors that determine tDCS effectiveness while developing more robust protocols.

Numerical simulation of the distribution of reverse currents in a practical alkaline water electrolysis stack immediately after electrolysis

In alkaline water electrolysis, reverse currents are reported to occur after rapid cell voltage change due to the electrodes oxidation state difference and such currents lead to electrodes degradation. The reverse current problems can be more severe in practical applications with larger electrode sizes and larger numbers of cells. In this study, reverse current with changes in the oxidation state of electrodes and potential distribution after sudden shutdown were analyzed based on a multi-physical simulation considering an electronic and ionic conduction in practical-scale. The effects of stack height, number of cells, and ionic resistance through the manifold on the reverse current distribution were investigated. The numerical results reveal that, especially under the condition of low manifold resistance and higher stack height, the discharge current extremely concentrated near the bottom of the edge electrode. This information is important for future stack development because this current concentration can cause severe stack degradation.

The influence of electrode geometry on the electrochemical performance of fabric-based screen-printed coplanar supercapacitors

Coplanar supercapacitors are promising flexible energy storage systems due to the excellent flexibility and tailored shapes and sizes of electrodes. However, the influence mechanism of electrode’ geometry parameter on the electrochemical performance of the flexible coplanar supercapacitors needs to be elucidated to realize the performance enhancement. Herein, the flexible coplanar supercapacitors with different thicknesses, widths and lengths of screen-printed electrodes were constructed on the cotton fabric substrates utilizing multi-walled carbon nanotubes ink and polymer gel electrolytes. The relationship between electrodes' geometry and overall electrochemical performance of flexible coplanar supercapacitors was detailed analyzed and demonstrated by employing equivalent series circuit model and electrode kinetic theory. Furthermore, due to the favorable aspect ratio and relatively low electrode and electrolyte resistance, the fabric-based coplanar supercapacitor with electrode size of 4 × 10 mm shows optimal electrochemical performance with areal capacitance of 3.08 mF cm−2 at 20 mV s−1, fast electrode response and effective kinetic process. Most importantly, the fabric-based supercapacitor exhibits excellent flexibility and cycling performance with capacitance retention rate over 79.6 % after 4000 charge and discharge cycles, indicating application potential in wearable electronic devices. The analysis and assessments of electrodes' geometry provides theoretical reference for the electrode design and optimization of flexible coplanar supercapacitors.

Effect of boron doping levels on the microstructure and characteristics of high-quality boron-doped diamond electrodes prepared by MPCVD

In order to fully understand the relationship between boron doping level and material characteristics, a series of high-quality boron-doped diamond (BDD) electrodes with different boron doping levels (B/C ratios = 1000–5000 ppm) were prepared on a silicon substrate using a self-designed microwave plasma chemical vapor deposition (MPCVD) reactor in this study. The relationship between surface morphology, structural composition, chemical bonding state, electrical conductivity and electrochemical properties of BDD electrodes was investigated systematically. With the increase of boron doping level, the grain size of the BDD electrode tends to decrease, the crystal orientation tends to be dominated by (111) orientation, the conductivity increases sharply and then gradually stabilizes, while the width of the potential window tends to decrease (4.39 V to 3.95 V from 1000 ppm to 5000 ppm), and the reversibility and stability of the electrode improves significantly. In addition, such high-quality BDD electrodes also exhibit a higher sensitivity (0.1176 μAμM−1 cm−2) and lower limit of detection (0.276 μM) in the detection of dopamine. The boron doping level in BDD electrodes plays a prominent role in material characteristics such as surface morphology, structural composition, chemical bonding state, electrical conductivity and electrochemical properties. Despite the challenging synthesis of pure sp3 carbon materials at high boron doping levels, the BDD electrodes prepared in this study exhibit high quality without sp2 defects even with high boron doping levels, and possess extremely low resistivity (~10−3 Ω·cm) and a wide electrochemical potential window (~4 V), which has not been achieved in other previous research works and offer great potential in the electrochemical applications of BDD electrodes.

Helical Microfilament‐Electrode‐Based Semi‐Implantable Biosensors for In Vivo Electrochemical Detection

Semi‐implantable devices have shown potential for real‐time sensing of physiological information in vivo. For glucose detection in diabetes, semi‐implantable electrodes have the ability to measure glucose concentration directly from interstitial fluid (ISF) with high accuracy and continuous monitoring performance. However, electrochemical detection by the amperometric method is limited by the electrode size, which can restrict signal magnitude and sensitivity of the implantable microfilament electrode. To address this limitation, a semi‐implantable helical microfilament‐based glucose electrode (HMGE) is developed. The helical structure of the HMGE enhances the electrochemical sensing area, while the coating with carbon nanotube and poly(3,4‐ethylene‐dioxythiophene): polystyrene sulfonate provides an electron‐transfer interface for electrochemical sensing. The HMGE exhibits high selectivity and sensitivity for glucose detection. Through in vitro experiments, the sensitivity of HMGE is improved by about 7 times compared with that of the non‐helical structure. In in vivo studies in rats, it is demonstrated that HMGE system can continuously monitor glucose concentration changes in ISF with reasonable accuracy after signal calibrations. Furthermore, a circuit‐sensing system and smartphone application are developed to support the operation of HMGE system as a phenotype. The HMGE presents a promising semi‐implantable device for monitoring various electrolytes, metabolites, and biochemical signals in vivo.

Bio-potential noise of dry printed electrodes: physiology versus the skin-electrode impedance

Objective. To explore noise characteristics and the effect physiological activity has on the link between impedance and noise. Approach. Dry-printed electrodes are emerging as a new and exciting technology for skin electro-physiology. Such electrode arrays offer many advantages including user convenience, quick placement, and high resolution. Here we analyze extensive electro-physiological data recorded from the arm and the face to study and quantify the noise of dry electrodes, and to characterize the link between noise and impedance. In particular, we studied the effect of the physiological state of the subject (e.g. rapid eye movement sleep) on noise. Main results. We show that baseline noise values extracted from dry electrodes in the arm are in agreement with the Nyquist equation. In the face, on the other hand, the measured noise values were higher than the values predicted by the Nyquist equation. In addition, we studied how different electrode properties affect performances, including electrode size, shape, and material properties. Significance. Altogether, the results presented here provide a basis for understanding dry electrode performances and substantiate their great potential in electro-physiological investigations.

Scanning Local Redox on 10 Micron Spots on a Monolith Electrode to Quantify Multiple Analytes at 10 Attomolar Sensitivity with Dynamic Range of Seven Orders of Magnitude

Electrochemical transduction is arguably the most prolific and impactful method to sense chemicals and biochemicals. For example, electrochemical methods have the distinct advantage to quantitatively measure nucleic acid (NA) sequences at a limit of quantification (LOQ) of 10 attomolars and high sequence specificity. The sensitivity and dynamic range significantly surpasses optical/spectroscopic, gravimetric, and electronic transduction methods. However, electrochemical sensing cannot be easily multiplexed. Only one analyte per electrode can be measured. Furthermore, the electrode size, i.e., the sensor area, for reasonable redox current, is typically, at least 1 mm2 for small analyte concentration.A fully automated instrument, called the Scanning Electrometer for Electrical Double-layer (SEED), will be described that addresses the abovementioned limitations. SEED, based on differential optics, quantitatively measures electrochemical process by changes in the electrical double-layer (EDL) and the surface during electrochemical process. The instrument can be operated in three modes: (a) reflectivity; (b) interferometry; (c) spectroscopy. The instrument can be toggled between the three modes without moving the sample or realigning the optics. The three modes measure the structural change at the surface, change in charge state of the EDL, and change in the molecule’s electronic structure due to the electrochemical process.The principle will be described with following applications in material science, sensing and life science: (i) miRNA profiling at LOQ of 10 attomolar with dynamic range of seven orders of magnitude; (ii) single base mutation in NA sequence; (iii) heavy metal ion detection from ppt to ppb levels; (iv) spectroscopic measurement during redox on graphene; (v) Langmuir adsorption of ions on Au electrode; and (vi) direct measurement of potential of zero charge (PZC). Figure 1

Operando X-Ray Imaging of Gas-Electrolyte Behavior in the Zinc-Air Batteries

Zinc-air batteries have the potential to be widely used due to their high energy density, low cost, and safety. However, some problems with the electrolyte in the batteries have prevented their widespread use. For example, hydrogen evolution can occur in the zinc anode, reducing the battery's usable capacity. The oxygen reduction performance of the air electrodes is also a challenge, as the electrolyte, catalyst, and gas all interact with each other. Understanding the behavior of the electrolyte and gas is crucial to addressing these problems. Previous analyses, such as operando gas analysis, have provided some insights, but they have not been able to pinpoint the specific locations where these problems occur. More detailed, real-time observation of the cell, known as operando visualization, is needed to better understand these issues.In this study, x-ray imaging is conducted to visualize the electrolyte behavior inside a zinc-air battery. X-rays are highly permeable and nondestructive, allowing for real-time, operando observation of electrolytes in the battery. This allows for the simultaneous observation and comparison of the electrochemical performance of the cell and the behavior of the electrolyte during open circuit voltage (OCV), charging, and discharging.To obtain clear x-ray images, the x-ray permeable cell shown in fig.1 is designed with a small electrode size (2 x 10 mm) and an ABS polymer cell casing. This allowed for sufficient contrast in the acquired images, enabling the observation of the liquid electrolyte between the electrodes and inside the catalyst layer. The anode of the cell was made of zinc, and the cathode was a mixture of carbon black, PTFE binder, and LCCO (La0.6Ca0.4CoO3) catalyst that was coated onto carbon paper as gas diffusion layer (GDL) using a hot pressing process. A 6 mol/L KOH aqueous solution is used as the electrolyte. X-ray images were obtained using a Rigaku nano3DX and a molybdenum target. During the observation, the charge/discharge condition was controlled using a potentio-galvanostat. The hydrogen gas (H2) concentration is also monitored using an electrochemical sensor.Figure 2 shows x-ray images of the cell near the air electrode in four different conditions: (a) without electrolyte, (b) with electrolyte, (c) during the discharge phase, and (d) during the charging phase. Because liquid electrolyte absorbs more x-rays than air, the areas with liquid electrolyte appear darker in the images than the areas without electrolyte (Figure 2 (a) and (b)). During the discharge phase, some bright circular shapes appear, which are thought to be bubbles (Figure 2 (c)). These bubbles are also generated during the charging phase (Figure 2 (d)), and it appears that the formation of the bubbles is not dependent on the cell voltage or current density. The experimental data from the H2 sensor shows that H2 concentration increased during the discharge phase, indicating that the bubbles contain hydrogen gas.The hydrogen evolution reaction (HER) in zinc-air batteries is a natural reaction given the electrochemical potential of hydrogen and zinc. Until now, the HER problem has only been discussed in relation to the open circuit voltage (OCV) and the charging phase. It was previously thought that HER hardly occurs during the discharging phase because the cell voltage typically decreases at this time. However, the experimental data shows that HER does not stop during the discharging phase. In addition, the researchers observed that the bubbles formed during this phase disrupt ion transfer efficiency, causing a drop in cell voltage.This study demonstrates the successful visualization of electrolytes inside a zinc-air battery using x-ray imaging. In addition, the researchers observed unexpected hydrogen evolution during the discharging phase. Since HER has a significant impact on the lifetime and safety of the battery, the mechanism behind HER during the discharging phase is an important problem for zinc-air batteries to address. Figure 1

Modeling the Coulombic Efficiency of the Aqueous Iron Electrode

The aqueous iron electrode is attractive for large-scale energy storage because of its long life and low materials cost. The redox potential of the Fe ↔ Fe2+ reaction is approximately 50 mV negative of that of the hydrogen evolution reaction. Hydrogen evolution therefore causes self discharge of the iron electrode during rest and competes with the iron reaction during charge. Here we model the effect of electrode design and cell operation on the coulombic efficiency of charging the iron electrode at modest charging rates (<C/20). Kinetic parameters (exchange current density and transfer coefficients) for the iron dissolution-precipitation reaction and for the hydrogen evolution reaction are estimated from experimental measurements of electrode overpotential and hydrogen generation rate. The volume change from Fe(OH)2 to Fe metal results in a significant increase in porosity during charge and results in change in electrochemically active surface area. The porous-electrode model includes transport in the electrolyte, Butler-Volmer kinetics, and change in volume and surface area.The model provides a theoretical explanation for experimental observations that coulombic efficiency decreases with decreasing charge rate, and that coulombic efficiency is lower in thicker electrodes. We then use the model to explore the impact for large-format cells of electrode size and design on coulombic efficiency.

Geometrical Characterisation of TiO2-rGO Field-Effect Transistor as a Platform for Biosensing Applications.

The performance of the graphene-based field-effect transistor (FET) as a biosensor is based on the output drain current (Id). In this work, the signal-to-noise ratio (SNR) was investigated to obtain a high-performance device that produces a higher Id value. Using the finite element method, a novel top-gate FET was developed in a three-dimensional (3D) simulation model with the titanium dioxide-reduced graphene oxide (TiO2-rGO) nanocomposite as the transducer material, which acts as a platform for biosensing application. Using the Taguchi mixed-level method in Minitab software (Version 16.1.1), eighteen 3D models were designed based on an orthogonal array L18 (6134), with five factors, and three and six levels. The parameters considered were the channel length, electrode length, electrode width, electrode thickness and electrode type. The device was fabricated using the conventional photolithography patterning technique and the metal lift-off method. The material was synthesised using the modified sol-gel method and spin-coated on top of the device. According to the results of the ANOVA, the channel length contributed the most, with 63.11%, indicating that it was the most significant factor in producing a higher Id value. The optimum condition for the highest Id value was at a channel length of 3 µm and an electrode size of 3 µm × 20 µm, with a thickness of 50 nm for the Ag electrode. The electrical measurement in both the simulation and experiment under optimal conditions showed a similar trend, and the difference between the curves was calculated to be 28.7%. Raman analyses were performed to validate the quality of TiO2-rGO.