Electrode Surface Research Articles

SECM Study for Surface-Grain-Resolved Hydrogen Oxidation Reaction Activity of Polycrystalline Pt Electrode

Introduction Carbon-supported Pt nanoparticles (Pt/C) are used as anode as well as cathode catalyst for polymer electrolyte fuel cell (PEFC). In general, electrochemical reactions that proceed at electrocatalyst surfaces are strongly depended upon their surface atomic arrangements. Therefore, to develop novel catalyst materials, guidelines of microstructural surface design of the catalysts are indispensable through clarifying various surface properties of the catalysts, such as surface atomic arrangements, size, and shapes and comprehensive understandings of the surface microstructures and catalytic properties should be required. From the above perspectives, fundamental studies for the electrocatalysis by using "well-defined" single crystal surfaces of Pt (Pt(hkl)) have been conducted to date [1]. However, gaps of material’s sizes between the surfaces of millimeter-sized single crystal and nano-sized particles make it difficult to understand practical catalytic properties of the nano-sized particles. To bridge the forementioned gaps, this study aims to clarify the dependences of hydrogen oxidation reaction (HOR) properties on micrometer-sized surface grains of a polycrystalline Pt electrode, through comparing two-dimensional (2D) surface mappings with micrometer resolution of surface grain orientations analyzed by an electron backscatter diffraction (EBSD) method and of hydrogen oxidation reaction (HOR) activities evaluated by a scanning electrochemical microscope (SECM) [2]. We successfully correlate the micrometer-sized surface grains and corresponding HOR properties. Experimental Polycrystalline Pt substrate (10mm × 10mm, 1mm thickness) was pre-annealed at 1000°C for 15 hours in ultra-high vacuum (UHV: ~10-7 Pa). The surface grain orientations of the polycrystalline electrode were analyzed using EBSD in air. For comparison of 2D mapping images of EBSD-analyzed surface grain orientations and SECM-evaluated HOR activities, ten-nanometer-size triangle shapes were marked by a nano indenter (TTX-NHT, Anton Paar) on the Pt substrate surface as signs of the positions. The polycrystalline Pt substrate surface thus prepared was cleaned by three cycles of Ar+ sputtering and annealing at 1000°C for 10 minutes alternately in UHV and, after that, HOR activities of the electrode was performed in 0.01M HCIO4 + 0.1M NaClO4 mixed electrolyte by SECM. 2D mapping image of micrometer-resolved HOR activities was collected by a scanning Pt-made microelectrode (φ = 10μm) with a distance of ca. 7μm between the microelectrode and polycrystalline electrode. Because a possible scanning region of the microelectrode was 200 µm square, a whole 2D mapping image of HOR activities (350µm × 650μm; Fig. 1(a)) was constructed by eight pieces of the 200 µm square images. Finally, by referring to the position markings made by the nano indenter, 2D images of surface grain orientations and HOR activities were combined with micrometer resolution. Results Fig. 1 shows 2D mapping images of (a) the surface grain orientations and of (b) HOR activities for the polycrystalline Pt electrode surface, respectively, where the grains having surface orientations close to (111), (110), and (100) are distinguished in blue, green, and red and purple in (a; right-hand-side invers pole figure) and the iT values of the scanning microelectrode currents that induced by HOR are presented by colors (b; of a right-hand-side indicator). Close correlations are identified between the surface grain orientations and corresponding HOR activities with micrometer resolution. From detailed comparisons of the two 2D mappings, the order of HOR activities is (111) oriented surface grains > (110) > (100). Notably, in the vicinities of specific grain boundaries, HOR activities changed within the same surface grains. In the presentation, we will discuss dependences of the orientations of surface grains, grain boundaries on corresponding HOR activities for the polycrystalline Pt and Ir electrodes. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan and Japan society for the promotion of science (JSPS).Reference[1] K. Hayashi, et al., Phys. Chem. Chem. Phys., 25, 2770-2775, (2023)[2] O. Wipf, et al., J. Electrochem. Soc. 167, 146502, (2020) Figure 1

Development of in-Situ Electrochemical Megabalanus Roseusgene Measurement System

In recent years, global warming due to greenhouse gases has become a serious problem, causing problems such as atmospheric CO2 concentration and temperature rise. On the other hand, since about 70% of the earth is ocean, it is expected that exploring changes in the ocean environment not only due to atmospheric gases but also due to greenhouse gases will lead to conservation of the global environment.In order to accurately understand and predict the marine ecological environment, we need to acquire chemical information such as CO2 concentration, salinity, and pH, physical information such as temperature and pressure, and biological information such as genetic analysis from multiple angles. Chemical and physical information can be obtained in real time by installing high-precision sensors on underwater robots. However, since biological information requires complicated operations and large equipment, it is generally obtained by conducting experiments on land after sampling water. Here, there is a concern that genetic measurements in the ocean may involve losses such as decomposition of biological samples and changes in traits between the time the seawater sample is collected and the sample is transported to the laboratory. Therefore, in order to more accurately understand the marine ecological environment, we aimed for in-situ gene measurement using an electrochemical biosensor that is compact and capable of continuous measurement.The purpose of this research is to detect the DNA of the larvae of Megabalanus roseus, which are fouling barnacles, using an electrochemical sensor. Megabalanus roseus attach to the ships, cooling waterway systems of thermal power plants, and nuclear power plants, causing problems such as increased fuel consumption and decreased flow of cooling water. We developed a sensor electrode by designing a probe with a complementary sequence to ACTAGT, a sequence unique to Megabalanus roseus (Table 1), and immobilizing it on the electrode surface. The probe has a thiol group at the 5' end and a mediator at the 3' end, forming a loop structure. When the probe captures the target, the loop structure is loosened, and the distance between the electrode and the mediator changes, reducing the electron transfer efficiency and making it possible to quantify the target (Fig. 1).A 25×11 mm screen-printed electrode (SPE : working electrode - carbon, counter electrode - carbon, reference electrode - Ag/AgCl) was used as the electrode. The working electrode was electrodeposited with gold, and after washing, 5 µl of the probe with a loop structure was dropped onto the gold electrode and allowed to stand overnight for modification. Loop formation of the probe was performed by heat treatment at 95° C. for 5 minutes, followed by standing at room temperature for 15 minutes and on ice for 5 minutes. After that, the probe was washed with PBS, and 10 µl of 5 mM Amine-reactive PES was added dropwise, left to stand for 1.5 hours, and then washed with PBS to modify the end of the probe with a mediator. Next, 10 µl of 10 mM 6-Mercapto-1-hexanol was added dropwise as a blocking agent, and after 1 hour, the electrode was washed with PBS and used as a probe-modified electrode.A mediator peak was confirmed by cyclic voltammetry (CV), confirming the modification of the probe. When target DNA was added thereto, the oxidation peak current decreased. This is thought to be due to the loop unraveling when the probe, which had a loop structure, captured the target DNA. When the probe has a loop structure, the mediator and electrode are close to each other, but when the loop is unraveled, the mediator moves away from the electrode, reducing electron transfer efficiency and reducing the oxidation peak. Figure 1

Sensitivity Improvement of Electrochemical Virus Detection through Morphology Control of CNT Electrodes

The global pandemic of influenza virus (IFV) and Covid-19 has created a strong need for the technology to measure viruses quickly and sensitively. Currently, PCR-based detection technology is used to accurately detect these viruses, however they lack immediacy as it takes several days for the viruses to grow to detectable amounts. A complementary method that allows immediate detection is an antigen testing that uses complementary substances (aptamers and antibodies) that specifically bind to target virus. Among them, electrochemical detection via cyclic voltammetry is being researched as a method that can measure target virus in solutions with high sensitivity and high speed. Since these utilize chemical reactions on the electrode surface, the material and surface morphology of the electrode are important factors that govern sensitivity. Previous research has reported that highly sensitive and robust virus testing can be performed by using carbon nanotube (CNT) films, which are chemically stable and have a large surface area, as chemical electrodes. However, the effect of the surface morphology of CNT films such as structures and defects has not been sufficiently studied.In this study, we attempted to increase the sensitivity of electrochemical virus testing by controlling the surface morphology of CNT films and increasing the amount of aptamer adsorption. The morphology of the CNT film was controlled through heat and non-heat laser processing by using 532 nm nano-second and/or pico-second pulsed lasers. The fabricated morphology was evaluated by SEM and polarized Raman spectroscopy. In addition to measuring the amount of aptamer adsorption for each morphology using ultraviolet spectroscopy, we also evaluated the detection sensitivity of IFV when using the CNT films as an electrochemical electrode. As a result, we achieved the high sensitivity and reliability IFV detection with fg/ml of the limit of detection. In the presentation, we will introduce the developed CNT morphology control technology and discuss the relationship between morphology and aptamer adsorption amount. Figure 1

Surface and Bulk Stabilization of Silicon Anodes Via in-Situ Formation of Li-M-Si Zintl Phases Using Multivalent Cation Additives

Silicon is drawing attention as the upcoming anode material for the next generation of lithium-ion batteries due to its higher capacity compared to commercial graphite. However, silicon anions formed during lithiation are highly reactive with binder and electrolyte components creating an unstable SEI layer and limiting the calendar life of silicon anodes. In this study, the reactivity of lithium silicide and the formation of unstable SEI layer is mitigated by utilizing the use of a mixture of Ca and Mg multivalent cations as an electrolyte additive for Si anodes to improve their calendar life. Ca and Mg ions in the electrolyte diffuse into silicon particles forming relatively thermodynamically stable quaternary Li-Ca-Mg-Si Zintl phases with less chemical reactivity, in an in-situ fashion, stabilizing the bulk. Ca and Mg cations also react with the F anions in the electrolyte, forming a layer of nanocrystalline CaF2 and MgF2 that is closely coated around the silicon particles. The CaF2-enabled new SEI is strong and dense, which effectively protects the silicon core from side reactions, leading to lower capacity decay after calendar aging at high voltage. To understand the mechanism of ternary/ quaternary Zintl phase formation and its dynamics upon lithiation/delithiation, high-resolution solid-state 7Li and 29Si nuclear magnetic resonance (NMR) are utilized to directly probe the local Li and Si environments on Si electrodes harvested from coin and pouch cells at various states of (de)lithiation. The effect of multivalent cation additives on bulk and surface of aged silicon anodes was studied by multiple structural characterization techniques such as Electron Microscopy, HRXRD, ex situ and operando solid-state NMR. The results show that the electrodes that are gone through cycling and calendar aging with multivalent cations tended to have less cracking on the electrode surface, less lithium trapping in the bulk and the presence of mixed cations enhances cation migration and formation of quaternary Zintl phases stabilizing bulk and forming a more stable SEI in comparison to baseline electrolytes.

Efficient Carboxylic Acid Synthesis through Electrolytic Reduction of CO2 using BDD Electrodes

Recent chemical advancements have brought a variety of products but also increased emissions of harmful substances, prompting the search for cleaner synthesis methods like organic electrolytic synthesis methods, using electrical energy for reactions. Meanwhile, with the urgent need to reduce CO2 emissions and achieve carbon neutrality, recycling and reducing technologies for CO2 have gained significant attention 1). This study focuses on electrolytic carboxylation, utilizing CO2 as a raw material, which presents a promising avenue for organic electrolytic synthesis, allowing the synthesis of high-value compounds from cost-effective materials using electrical energy as a reducing agent. Notably, it offers the advantage of producing less waste, positioning it as a robust option for industrial adoption centered on green chemistry. However, since electrocarboxylation reactions occur on electrode surfaces, conventional approaches utilize organic solvents and precious metals like platinum (Pt), prized for their corrosion resistance and durability. To address this challenge, we have directed our focus towards synthesizing boron-doped diamond (BDD) electrodes, incorporating boron into the diamond structure. BDD electrodes boast a wide potential window, high durability, and corrosion resistance, making them capable of inhibiting undesirable reactions and facilitating sustained synthesis. Herein, it aims to address challenges in electrolytic carboxylation reactions, enhance energy efficiency, analyze reactions using diamond electrodes, ultimately establish a new synthesis method contributing to carbon neutrality.A comparative analysis of BDD and platinum electrodes was conducted to confirm the superior performance of BDD. BDD electrodes were prepared using the microwave plasma chemical vapor deposition method, employing acetone and methanol as carbon sources and boron trioxide as the boron source. Plasma irradiation of a mixture of raw materials and hydrogen gas was used to deposit BDD on a silicon substrate. Prior to the experiment, the BDD surface underwent ultraviolet ozone treatment with oxygen to enhance stability and establish consistent initial conditions. Under N2 or CO2 atmospheric conditions, cyclic voltammetry (CV) was performed with a scanning rate of 10 mV/s in Bu4NBF4/acetonitrile (0.1 M) and acetophenone (0.01 M) to investigate the electrochemical behavior of BDD and Pt electrodes. CV studies were utilized to investigate the reduction potential. Finally, acetophenone was synthesized via constant current electrolysis under a CO2 atmosphere.Figure 1 displays the CV curves of a) BDD and b) Pt electrodes in acetonitrile solvent and acetophenone electrolyte, respectively. In the electrocarboxylation reaction, the electrochemical reduction of acetonitrile and CO2 occurs as a side reaction. Our findings indicate that the reduction of acetonitrile and CO2 does not occur at the reduction potential of acetophenone when using a BDD electrode. Conversely, when a Pt electrode is employed, acetonitrile is slightly reduced by the reduction potential of acetophenone, and CO2 reduction occurs as a side reaction. Figure 2(a) depicts the yield of atrolactic acid obtained using both BDD and Pt electrodes. In case of Pt electrode 13 % yield of atrolactic acid while in case of BDD electrode 25 % yield of atrolactic acid observed. These results demonstrate that the electrocarboxylation reaction efficiency of BDD electrodes is higher than that of platinum electrodes. Figure 2 (b) shows a schematic diagram of the electrocarboxylation reaction. Initially, acetophenone undergoes one electron reduction. The resulting substance reacts directly with CO2 and undergoes further reduction by one electron 2). This study showcases the potential of BDD electrodes for organic synthesis, particularly in the electrolytic carboxylation of acetophenone. References 1) S. Wang, T. Feng, Y. Wang, Y. Qiu, Chem. Asian. J. 17, e202200543 (2022).2) M. A. Stalcup, et al., ACS Sustainable Chem. Eng. 9, 10431-10436 (2021). Figure 1

A Parametric Study of Mathematical Model for Long-Term Localized Corrosion of Copper in Canadian Deep Geological Repository

The concept of Adaptive Phased Management, approved by Canadian federal authorities and implemented by the Nuclear Waste Management Organization, forms a comprehensive strategy for the long-term safe management of used nuclear fuel in Canada.1 The used nuclear fuel will ultimately be placed within a container in a deep geological repository (DGR). Current container designs employ steel vessels with a protective copper outer layer, strategically selected to reduce corrosion damage. The copper-coated container may be subjected to various corrosion mechanisms over time as the DGR environment evolves. Specific to this work and in the early aerated environment of the DGR, efflorescing salt impurities present on the container surface may lead to the formation of an Evan’s droplet. To understand the behavior of the copper-coated container with respect to localized corrosion and ensure the effectiveness of this protection strategy, a preliminary two-dimensional axisymmetric time-dependent model for the corrosion of copper under an Evans droplet was developed.2, 3 The mathematical model was developed using the finite-element method (COMSOL Multiphysics). Some unique features of the model are inclusion of six heterogeneous and fifteen homogeneous reactions, implicit calculation of nm-scale films, and treatment of the influence of films on surface concentrations and potentials. The model shows the time-dependent localized corrosion rates and depths, calculated for an elapsed time of ten years. It also shows time-dependent radial distributions for current density and surface coverage of films. The influence of oxygen conditions and temperature was included, and the model accounted for the influence of films on reaction rate constants. Preliminary results show that the corrosion of copper in the Evan’s droplet is almost uniform on the electrode surface. Temperature and oxygen concentration was shown to have a strong contribution to copper corrosion.The current version of the mechanical model has many parameters. Some parameters are obtained from PHREEQC thermodynamic software,4 some are selected to yield good results, and some are defined using expert judgement from the literature.While the number of parameters is very large, the impact of each parameter is constrained by the model. A parametric study is necessary to identify reasonable ranges of values and explore different conditions that may lead to localized corrosion of copper. For example, to switch the mechanism from kinetic control to mass-transfer control, the overall rate constants were increased by different orders of magnitude. The influence of both oxide film and salt film on rate constants reduction were also studied. Combining both the blocking effect of films on the copper surface and the control mechanism shift, simulations were completed to study the parameter space. The present work shows that the corrosion rate increased as rate constants were increased, and currents became limited by mass transport of oxygen.References NWMO, “Choosing a Way Forward. The Future Management of Canada’s Used Nuclear Fuel. Final Study,” Nuclear Waste Management Organization, Toronto, Ontario, 2005.C. You, S. Briggs, and M. E. Orazem, “Model Development Methodology for Localized Corrosion of Copper,” Corrosion Science, 222 (2023), 111388.C. You, Y. Chuai, S. Briggs, and M. E. Orazem, “Model for Corrosion of Copper in a Nuclear Waste Repository,” Corrosion Science, 226 (2023), 111658.PHREEQC Version 3, United States Geological Survey, 202, https://www.usgs.gov/software/phreeqc-version-3. AcknowledgementThis work was supported by the Nuclear Waste Management Organization, Canada, under project 2000904.

Lithium Electrodeposition Process in Various Hydrogenated Electrolyte Solutions

Introduction: The lithium metal anode, which is attracting attention as a high-capacity next-generation anode material, is hindered in practical application by the formation of dendritic deposits known as lithium dendrites during charging (electrodeposition). One method to achieve dendrite-free electrodeposition of Li involves the addition of a small amount of water to an electrolyte containing LiPF6, leading to the formation of HF through hydrolysis. During electrodeposition, LiF precipitates along with lithium, resulting in the formation of columnar lithium, which is known to inhibit dendrite formation [1]. In this study, therefore, we investigated the influence of solvent properties on the columnar structure of lithium by adding a small amount of water to electrolytes containing LiPF6 in three different solvents with varying properties, comparing the mass changes on the electrode surface and the composition of the deposits during lithium electrodeposition.Experiment: Three solvents (pure dimethyl carbonate (DMC), a mixture of ethyl carbonate (EC) and DMC (v/v = 1:1), and a mixture of EC and diethyl carbonate (DEC) (wt/wt = 1:1)) were used for the experiments after adding 1 M LiPF6 and approximately 50 ppm water, ensuring sufficient progress of hydrolysis. Copper foil or copper-coated quartz crystal microbalance (QCM) electrodes were employed as the working electrode, and lithium foil was used as the counter electrode. Lithium electrodeposition was conducted at a constant current density of -0.5 mA cm-2 for 2 hours, during which the mass changes and impedance variations were monitored using QCM and electrochemical impedance spectroscopy (EIS), respectively. Additionally, composition analysis of the deposited lithium after electrodeposition was performed using X-ray photoelectron spectroscopy (XPS).Results and Discussion: The rate of hydrolysis of LiPF6 by the added water varied significantly depending on the solvent, with durations of 2 days for DMC alone, 8 days for EC/DMC, and 20 days for EC/DEC. This difference is seemed to be due to variations in the dissociation of LiPF6. When a current was passed through the copper electrode, a plateau region of cell voltage due to HF reduction was maintained for 10 to 20 seconds around 2 V, followed by a decrease in voltage and a constant voltage of ca. -0.2 V, indicating the onset of lithium deposition. The ratio of mass increase during lithium deposition (mass per electron; MPE) was in the reverse order of the rate of hydrolysis, with EC/DEC > EC/DMC > DMC. Additionally, the resonant resistance increased significantly in the order of DMC > EC/DMC > EC/DEC. Based on the mass changes and the morphology of the deposition mentioned later, it is highly probable that an increase in viscosity and density of the electrolyte due to side reactions, or an increase in surface area due to dendrite formation, occurred. In EC/DEC and EC/DMC, a characteristic blue-colored precipitate indicative of columnar lithium structures was observed, while in DMC, it was gray, showing lithium dendrite. XPS analysis revealed that LiF was dominant on the surface of the deposited lithium in all electrolytes, but there were significant differences in the amount of surface carbon, with EC/DEC > EC/DMC > EC/DEC. These results suggest that differences in EC content lead to variations in the dissociation and viscosity of the electrolyte, which in turn affect the morphology of the deposited lithium.

Theoretical Studies of Hydrogen Evolution Involving Imidazolium Proton Donors

The hydrogen evolution reaction (HER) is an important electrocatalytic reaction used for the electrochemical production of hydrogen gas. Its reverse reaction, the hydrogen oxidation reaction, is used to produce protons used in electrocatalytic reduction reactions for various electrochemical energy conversion and storage applications. While many fundamental studies have analyzed interfacial reactivity in aqueous HER, analogous mechanistic understanding of HER reactivity in nonaqueous media remains limited.In this presentation, periodic density functional theory (DFT) calculations are applied to mechanistic studies of HER on Pt(111) using various imidazolium proton donors. These studies incorporate analyses of imidazole adsorption and potential-dependent activation energies. The conjugate bases of imidazole adsorb strongly to the electrode surface. Yet, the adsorption geometries and energetics are sensitive to substituent effects and isomeric configurations at the interface. The potential-dependent binding geometries and adsorption energies of different imidazoles adsorbed to Pt(111) are analyzed in a dielectric continuum implicit solvent. These calculations demonstrate how imidazole derivatization and electrode surface charge impact the adsorption of imidazole conjugate bases during HER. To gain insights into the kinetics of the elementary Volmer and Heyrovsky steps of HER, potential-dependent reaction energies and activation barriers were calculated using the charge extrapolation method. Energetics were calculated for different electrode potentials by modifying the coverage of protons. This approach was used to develop relationships between reaction thermodynamics and kinetics via Brønsted–Evans–Polanyi relationships for various imidazoles, where this relationship gives charge transfer coefficients in the Butler–Volmer equation. The goal of assessing these reaction parameters is to enhance understanding of charge transfer processes and molecular interactions at the electrode-electrolyte interface, which is essential for the design of high-efficiency energy conversion and storage devices. The potential-dependent adsorption behavior and kinetics of elementary proton-coupled electron transfer steps are used to understand the reaction kinetics of hydrogen evolution in a nonaqueous imidazole-based electrolyte through comparisons to voltammetry measurements. Through these analyses, we identify kinetic trends across functionalized imidazoles, providing valuable perspectives for the development of catalytic systems and energy storage technologies.

Investigating the Impact of Blocking Monolayer Architecture on the Performance of Electrochemical DNA Biosensors in Microfluidic Channels

An electrochemical nucleic acid biosensor typically involves the immobilization of DNA strands onto a surface, which serves as a recognition element for specific DNA or RNA target molecules.1-3 DNA strands can be single-stranded or double-stranded, and their immobilization onto a surface is crucial for sensing applications. This allows the formation of monolayers which is often used to prevent nonspecific adsorption of interfering molecules onto the surface. This layer acts as a barrier, allowing only specific interactions with the DNA target molecules or analytes of interest. Traditionally, redox mediators such as ferrocyanide/ ferricyanide that undergo reversible oxidation-reduction reactions are often used to detect hybridization of DNA targets with immobilized complementary DNA probes. Under these conditions, the heterogeneous charge transfer rate of redox mediators at the electrode surface is often a key factor taken into account to interpret the sensitivity and efficiency of the biosensor.3-5 In this work, with a set of experiments carried out by hydrodynamic voltammetry and impedance spectroscopy at channel microelectrodes, we propose a new approach supported by numerical modeling to highlight the influence of the mass transport of redox mediators on the response of DNA biosensors. Contrary to what is commonly accepted in the literature, we showed that the presence of DNA monolayers acting as blocking monolayers does not affect the charge transfer rate of redox mediators, regardless of the electrode accessibility (surface coverage). We demonstrated that under flow conditions, the current response of the biosensors was controlled by the mass transport rather than the charge transfer rate of redox mediators. This phenomenon was attributed to the nonlinear effects of diffusion-convection of the redox mediators at the remaining active sites, thereby affecting the overall kinetics of the transduction signal. These experiments, coupled with numerical calculations, allowed us to compare the performance of DNA biosensors obtained with different blocking monolayers and to evaluate the average size of the active sites. In this model, they were assumed to be small compared to the electrode size.This study constitutes an important advance in the field of sensors or biosensors, in the broad sense, as it points out the influence of parameters controlling mass transport and therefore the performance of electrochemical DNA biosensors, such as the density of DNA monolayers, the composition of the blocking agents, and size of holes (active sites). REFERENCES 1 Slinker, J. D.; Muren, N. B.; Gorodetsky, A. A.; Barton, J. K. Multiplexed DNA-Modified Electrodes. J Am Chem Soc 2010, 132 (8). 2 Horny, M. C.; Lazerges, M.; Siaugue, J. M.; Pallandre, A.; Rose, D.; Bedioui, F.; Deslouis, C.; Haghiri-Gosnet, A. M.; Gamby, J. Electrochemical DNA Biosensors Based on Long-Range Electron Transfer: Investigating the Efficiency of a Fluidic Channel Microelectrode Compared to an Ultramicroelectrode in a Two-Electrode Setup. Lab Chip 2016, 16 (22). 3 Zambry, N. S.; Awang, M. S.; Beh, K. K.; Hamzah, H. H.; Bustami, Y.; Obande, G. A.; Khalid, M. F.; Ozsoz, M.; Manaf, A. A.; Aziah, I. A Label-Free Electrochemical DNA Biosensor Used a Printed Circuit Board Gold Electrode (PCBGE) to Detect SARS-CoV-2 without Amplification. Lab Chip 2023, 23 (6). 4 Tersch, C.; Lisdat, F. Label-Free Detection of Protein-DNA Interactions Using Electrochemical Impedance Spectroscopy. Electrochim Acta 2011, 56 (22). 5 Cardoso, A. R.; Moreira, F. T. C.; Fernandes, R.; Sales, M. G. F. Novel and Simple Electrochemical Biosensor Monitoring Attomolar Levels of MiRNA-155 in Breast Cancer. Biosens Bioelectron 2016, 80.

The Mechanism and Enhancement of Imidazolium-Mediated CO2 Reduction on Silver in Non-Aqueous Electrolytes

Electrocatalysis of carbon dioxide reduction reaction (CO2RR) is known to proceed at lower overpotentials with the presence of ionic liquids (ILs) in the electrolyte. However, the role of ILs in modulating CO2RR, even for the most studied 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) remains unclear. In this study, the electric field and the hydrogen bonding effects induced by [EMIM][BF4] and hydrogen bond donors (HBDs), including water and a series of alcohols, in acetonitrile were examined on Ag. By employing voltammetry, in-situ enhanced Raman spectroscopy (SERS), and density functional theory (DFT) calculations, we reveal that the initial electron transfer to CO2occurs at reduced overpotentials when it is confined between the [EMIM]+ ring planes and the electrode surface. This confinement of CO2 stabilizes it at the interface and enables its conversion to CO, accompanied by the generation of carbene and water as by-products. Furthermore, our findings suggest water (< 0.5 M) acts as the hydrogen bond donor as opposed to serving as the primary source of free protons. Based on this finding, we further show how the extend of hydrogen bonding as varied by various alcohols alter the microenvironment in synergy with [EMIM]+ at the electrode-electrolyte interface for fine tuning of the thermodynamics of CO2RR. The clarified role of the imidazolium based ILs and hydrogen bond donors, and the demonstrated enhancement in CO2RR will advance non-aqueous electrolyte development and inform future kinetic studies.

Chemical Prelithiation of Silicon Oxide Anodes for Improved Performance in Lithium-Ion Batteries

Si/SiOX-based materials possess significant potential as an anode in Li-ion batteries, due to their high capacity, stable cycling performance and the volume expansion buffering of the SiOX matrix upon lithiation of silicon nanodomains. However, one of the main challenges is their low initial coulombic efficiency (ICE), due to SEI formation and irreversible parasitic reactions which trap Li ions inside the electrode matrix or at the interface. Prelithiation aims to compensate for the large initial irreversible capacity losses, which can be achieved by introducing active lithium directly into the anode material before cycling.Through chemical prelithiation, the electrode coating or active material powder is brought in contact with a reactive Li-containing precursor solution via immersion, which allows a direct reaction at the surface. The precursor system ideally requires a sufficiently low redox potential to achieve (partial) prelithiation of the SiOX matrix, while minimizing full Si lithiation and Li plating at the electrode surface. Lithium-Arene complexes dissolved in (cyclic) ether solvents have been shown to have adequate reducing strength (0.2-0.3V vs. Li/Li+) to allow these redox reactions.In this study, the effects of chemical prelithiation on the battery performance are evaluated inside a half-cell, mainly focusing on the initial cycles. Additionally, the effect of prelithiation on the morphology and composition of the electrode (active) material will be investigated using electron microscopy (SEM) and X-ray diffraction (XRD), including the effect of air exposure on the phase stability. Furthermore, the chemical state of the sample surface is studied, giving deeper insights into its interfacial reactivity and composition. Ultimately, this study aims to create a better understanding of the advantages and disadvantages of this prelithiation method on Si/SiOX-based anodes, paving the way for the development of more efficient lithium-ion batteries.

Gold Deposited Gas Diffusion Electrodes by RF Sputtering and Their CO2 Reduction Activity to CO

The electrochemical CO2 reduction reaction (CO2RR) is attracting attention as a promising method to convert CO2 into value-added products such as CO, which is used as a feedstock in the Fischer-Tropsch process. Previous research demonstrated that precious metal catalysts, such as Ag or Au, proceed CO2 reduction to CO generation with high efficiency[1]. Despite their high Faradaic efficiency (current efficiency) and current density in using porous gas diffusion electrode (GDE) systems, a higher utilization efficiency of those catalysts is needed due to their high cost of those catalysts. Based on the above background, in the present study, we employed the sputtering process as a direct formation method of catalysts’ nanoparticles on the catalyst layer on GDEs. We used gold as a model catalyst, fabricated Au-supported GDEs (Au-GDEs), and evaluated their CO2RR activity. Au-GDEs were fabricated using an RF sputtering process, and Au nanoparticles were directly deposited onto commercially available GDEs. The thicknesses of the catalysts’ layer were controlled by adjusting the sputtering time. The Au-modified GDEs with the conventional spray-coating method were also prepared using Au nanoparticles synthesized by a conventional solution process using citric acid as the reduction agent(Au_Spray) [2] for comparison. The CO2RR activity was evaluated by galvanostatic measurements using 1 M KHCO3 as electrolytes. Fig. 1(a) shows a cross-section scanning electron microscopy (SEM) image of an Au-GDE with a typical catalyst layer thickness of 100 nm (Au_100). The catalyst layer composed of Au (the white part of the figure) was uniformly formed on the surface of GDE. The X-ray absorption structure (XAS) analyses revealed that the valence state of Au was Au(0), and that the catalyst layer on the GDEs was composed of Au nanoparticles. Next, the CO2RR activity of the Au-GDE was evaluated. Carbon monoxide (CO) was detected as the main CO2RR product, and formate (HCOO−) and hydrogen (H2) as a side reaction product were also detected. The effect of film thickness of Au-GDE on CO2RR selectivity was evaluated at a current density of 50 mA cm-2. Au-GDE with a film thickness of 10 nm (Au_10) and Au_100 produced CO with the Faradaic efficiencies (FEs) of 72.7 % and 79.8 %, respectively. The FEs of hydrogen evolution reaction (HER) of Au_10 and Au_100 were 26.1% and 10.3%, respectively. The CO efficiencies for Au_10 and Au_100 were significantly higher than those of Au_Spray, which had a similar Au loading to that of Au_100. The higher CO selectivity of the Au-GDEs prepared by sputtering might be attributed to the higher coverage of Au on GDEs, which was confirmed by SEM-EDX mapping.The potential dependence of partial current density for CO (j CO) normalized by Au mass loading was evaluated as an indicator of Au utilization efficiency for CO2RR (Fig. 1(b)). The electrode with a catalyst layer thickness of 10 nm showed the 1882 A g-1 (potential of -0.85 V vs. RHE). As far as we know, this is the highest value among the Au-based electrodes using GDEs [3]. The value is about one order of magnitude higher than that of Au_Spray. This high CO production activity can be attributed to the formation of a thin Au catalyst layer composed of Au nanoparticles on the electrode surface by sputtering. [4] The results of the electrode structure analysis and details of the CO2RR activity will be discussed in the presentation.[1]A. Fen wick et. al., ACS Energy Lett., 2022, 7, 871−879 [2] X. Ji et. al., J. Am. Chem. Soc., 2007, 129, 13939–13948 [3] M. Sassenburg et. al., ACS Appl. Energy Mater., 2022, 5, 5983–5994. [4] T. Yamada et. al., in preparation. Figure 1

Effect of Carbonate Solvent Additives in Electrolyte on the Self-Discharge Phenomenon in Organic Electrical Double Layer Capacitors

As a result of industrialization, technological progress, and the growing global population, energy consumption worldwide is skyrocketing. Researchers are thriving to seek high power density storage device to meet these escalating energy demands. Electrical Double Layer Capacitors (EDLCs) also known as a supercapacitor, are energy storage devices that store energy by Coulombic attraction between ions, polarized solvent on the surface of the activated carbon electrodes to form an electric double layer without involving chemical reactions. EDLCs display some remarkable characteristics such as high-power density, ultrafast charge/discharge rates, and long cycle life, surpassing conventional lithium-ion batteries. These features make EDLCs ideal for a wide range of applications, including portable devices, energy backup systems, and electric vehicles.However, the self-discharge effect in EDLCs is a deadly drawback that decrease the shelf life of EDLCs and impeding its practical applications. This phenomenon refers to the spontaneous voltage decay between the electrodes when the capacitor is under open-circuit potential after being charged, leading to a reduction in the stored charge without any external connection. This voltage declination is a complex process therefore, various mechanisms have been proposed to elucidate this phenomenon. There are primarily four mechanisms leading to the self-discharge. First, the internal short-circuit caused by imperfect seal of EDLCs leading to ohmic leakage current. Second, the uneven distribution of pore sizes in activated carbon electrodes leads to a higher resistance for ions to penetrate deeper into the material, resulting in ion accumulation on the surface during short charging times. This accumulation causes an uneven distribution of electron energy in the electrode material. After disconnecting, electrons rearrange to achieve overall energy consistency, while ions gradually redistribute and move into the smaller micropores within the activated carbon electrode. This phenomenon is referred to as charge redistribution effect. Third, Faradic current in EDLCs occurs due to redox reactions, stemming from the decomposition of the electrolyte or chemical reactions involving impurities within the electrolyte. Lastly, during the charging process, ions accumulate at the electrode surface, creating a concentration gradient between the electrodes and the electrolyte. As a result, ions gradually diffuse back into the bulk electrolyte until reaching equilibrium. Addressing self-discharge is paramount in ongoing research efforts.Electrolyte solutions are critical components in EDLCs, providing a medium for ion transport between the electrodes. The electrolyte solution is typically composed of a supporting electrolyte dissolved in a solvent, and the choice of solvent can significantly impact the performance of the device. This study delves into the impact of electrolyte solvent additives in the electrical double layer of EDLCs, leading to varied self-discharge performances. In this report, five commonly-used organic carbonate solvents in EDLCs, were selected to investigate their effects on the self-discharge phenomenon. Cyclic carbonate solvents, such as EC and PC, are known to possess high dielectric constants, high viscosities and high flash points. In contrast, linear carbonates e.g., DEC, DMC, EMC have low viscosities, low dielectric constants and low flash point. By incorporating carbonate solvents into the 1M TEABF4/PC (Tetraethylammonium tetrafluoroborate/propylene carbonate) commercial electrolyte, the performance of five supercapacitors , minimal deviation in electrochemical analyses such as CV and GCD was observed. However, significant differences emerged in EIS, elucidating the varying degrees of self-discharge phenomena. These differences in self-discharge mechanisms across the five EDLCs stemmed from the distinct dielectric constants and molecule sizes of the five solvent additives (i) Low dielectric constant and large molecule size, as seen in DEC (239.4h) and EMC (165.1h), contributed to increased interfacial impedance which effectively prolonging self-discharge compared to commercial one (145.7h). Conversely, the DMC with smaller interfacial resistance initially exhibited lower voltage decline due to reduced charge redistribution effects. However, its rapid ion diffusion process from carbon pores to electrolyte resulted in the fastest self-discharge of DMC (124.7h). (ii) High dielectric EC competes for solvation coordination, reducing interfacial resistance and enhancing intermolecular interaction. This, in turn, leads to the formation of a denser electric double layer (EDL) with EC, therefore decelerating the self-discharge process (205.9h) in EDLCs. In summary, the study emphasizes the significance of solvent additive selection and demonstrates a simple, safe, and cost-effective method to prolonging the self-discharge duration of DEC to more than 1.5 times that of the commercial one, significantly inhibiting the critical self-discharge issue in supercapacitors. Figure 1

Water Treatment Using Boron-Doped Diamond Powder-Packed Electrolysis Flow Cell

Water treatment by electrolysis can decompose persistent organic compounds, such as low-molecular-weight organic compounds in urine, which cannot be decomposed by microbial water treatments, into H2O and CO2. Anodic oxidation is being considered for use as one of the processes in the water reclamation system required for manned space exploration. Boron-doped diamond (BDD) electrodes can generate efficiently OH radical, which is a strong active oxidizing species, when high potential is applied in aqueous solution. In addition, BDD electrodes are known to be useful as electrode materials for electrolytic water treatment because of their physical and chemical stability. However, BDD electrodes are usually thin films, so their shape, size, and the configuration of electrolytic cells are restricted. Boron-doped diamond powder (BDDP)-packed electrolysis flow cell has been reported to be useful for water treatment with high efficiency because of the large electrode surface area. In this study, the BDDP-packed electrolytic flow cell with a closed system was developed for improvement of the decomposition efficiency.BDDP was prepared by using commercially available diamond powder with a particle size of 40-60 μm as a substrate material and depositing a BDD layer on its surface by microwave plasma CVD. The BDDP-packed electrolytic flow cell is as shown in Figure 1a. A plastic cylinder with an inner diameter of 1 cm was bonded to a glass filter (particle holding capacity: 20-25 μm, diameter: 10 mm), and a Pt wire was placed as a current collector above the filter. 0.8 g of BDDP was packed into the filter without a binder so that it was in full contact with the current collector. Electrolysis of 50 mL of 0.1 M Na2SO4 solution containing 50 μM methylene blue (MB) was performed for 60 min at a constant voltage of 5 V. The MB concentration after electrolysis was estimated by UV-vis absorption spectroscopy. In addition, the chemical oxygen demand (COD) of the electrolyte was measured before and after electrolysis.The result of MB constant voltage electrolysis with the BDDP-packed electrolysis flow cell is shown in Fig. 1b. MB was not sufficiently decomposed at a flow rate of 2.0 mL/min. The reason for this is thought to be that the bubbles generated on the BDDP surface caused insufficient contact between the BDDP. When the flow rate was increased to 20.0 mL/min to flush out all bubbles, about 90% MB degradation was achieved in 15 min and about 99% in 30 min. The higher the flow rate, the faster the MB concentration decreased. These results suggest that the closed BDDP-packed electrolysis flow cell allows bubbles generated on the electrode surface to be quickly flushed out with the treated water. The COD of the electrolyte before and after the electrolysis was measured and it ranged from 42.2 to 21.9. The decrease in COD suggests that part of MB was completely converted to CO2. In the future, we intend to quantitatively clarify the urine treatment capacity of the cell and apply it to a water recovery system in space. Figure 1

Moss-like Growth of Metal Electrodes: On the Role of Competing Faradaic Reactions and Fast Charging

Uncontrolled crystal growth during electroreduction of reactive metals in liquid electrolytes produces mossy metal deposits. Here we use electroanalytical Rotating-Disk Electrode (RDE) studies to elucidate the origin of moss-like growth of metals. We report that competing Faradaic reactions occurring on the electrode surface is the source of the phenomenon. A moss-like growth regime can be accessed by subtle shifts in electrolyte chemistry and deposition rate. Specifically, for Zn—a metal that conventionally is not known to form moss-like electrodeposits—obvious moss-like patterns emerge at low-current densities in strongly-alkaline electrolytes that undergo electroreduction to form an interphase. Conversely, under conditions where the rate of metal electroplating is large relative to that of other competing Faradaic reactions, it is possible to eliminate the moss-like growth. We further evaluate this principle in Li metal deposition and again find that the typical moss-like electrodeposit morphology of Li can be eliminated. As an empirical rule, an applied current density i that satisfies 10 is < i < 0.8 ilim could suppress instabilities giving rise to porous growth patterns. Our findings open up a new approach for achieving favorable metal deposition morphology and fast charging in next-generation batteries.

In Situ Probing Electrified Interfacial Molecular Anion Structures at Atomically Flat Gold Electrode

Electrochemical interfaces—buried between electrodes and electrolytes—are notoriously difficult to probe, and enormous efforts, both experimentally and computationally, have been devoted to this endeavour. Although some progress has been made, the microscopic structures of electrochemical interfaces remain elusive and a great challenge in physical sciences.[1] Answering this question is not only of fundamental interest but also of technological importance in a broad range of research areas in science and technology, to name a few, energy storage in supercapacitors, electrocatalysis of relevance to energy and environmental applications, self-assembly of colloidal particles, ion transport across biological membranes, and mineralization processes in earth science. Despite its significance, molecular-level understanding of Electrified Double Layer (EDL) is largely missing, owing to its complexity and small scale making it difficult to probe. Because of the advent of advanced experimental (e.g., synchrotron-based techniques and Raman spectroscopy) and computational methods [e.g., ab intio molecular dynamics (AIMD)], it is not until recently that the microscopic structures of EDL have started to be unveiled. [2,3] In this study, we employ in-situ Shell Isolated Nanoparticle Enhance Raman spectroscopy (SHINERS) to investigate the structures of electric double layers at electrochemical interfaces. Specifically, we focus on understanding the arrangement and surface interaction of anions on electrified gold single-crystal electrode surfaces under varying bias potentials. We discuss how these ions orient themselves and interact with the electrode surface, and how these interactions influence local permittivity and ion-surface attraction, ultimately impacting the structure and behavior of the EDL and electrochemical processes.[1] Le et al., Sci. Adv. 2020; 6[2] Li et al.,Nature Materials, 2020; 18[3] Wang et al., ,Nature, 2021;600

Printed for Performance: Harnessing the Electrochemical Potential of Prussian White Thick Electrodes v ia 3D Printing

The development of Prussian White (PW, Na1.92Fe[Fe(CN)6]) for water-based inks for thick, structured electrodes will be presented. PW is a derivative of Prussian blue analogues (PBA) and has the structural formula of AxM2[M1(CN)6]1-y, where A an alkaline metal such as Na or K, and M is usually a transitional metal such as Fe or Mn. Here, our PW is a strong Na-ion contender to replace Li-ion usage due to their low cost, efficient synthesis methods and comparable capacity to that Lithium iron phosphate of around 160 mAh/g. However, to match the performance of LFP, thick PW electrodes will need to be fabricated and here the mass transport of the electrode can be limiting. Thus, it is imperative to develop a Na-ion battery (NIB), that can exhibit both high energy and high power density, whilst maintaining cost and sustainability. To overcome this limitation of PW, the manufacturing of electrodes through careful battery design can be studied further to achieve a high performing cell.Thicker electrodes (>100 µm) have the potential to have both high power and higher energy, however there is a trade-off between both. When increasing the thickness of a standard two-dimensional (2D) electrode this lengthens the ionic pathways, limiting ionic transport across these thick electrodes. To overcome these restraints, we can introduce a 3D architecture within the electrode microstructure to maintain favourable, short ionic pathways hence, reducing the tortuosity within the electrode microstructure. This overcomes the mass transport limiting effects and now only the electron kinetic mechanism will be restrictive. One electrode deposition method that is used to create structured electrodes is by using a 3D printer (i.e., direct ink writing). Where electrode ink is loaded into a syringe and pressure is applied to extrude the ink through a nozzle.Prussian White is investigated here to see whether it has potential to be 3D printed via extrusion to create our desired thick and structured electrodes. 3D structured electrodes are achieved through tuning the ink rheology, these are compared against our standard 2D electrodes and with hopes to overcome the ionic and mass transport limits of 2D thick electrodes.Here, the overpotentials, impedance measurements and operando XRD from a synchrotron source will be evaluated, to understand how PW will transform under various electrochemical techniques. Further, there will be a direct electrochemical performance comparison between our 3D printed and 2D electrodes, through rate testing and Galvanostatic Intermittent Titration Technique (GITT). Here, we have seen the mass transport improve in our thick 2.8 mAh/cm2 3D printed electrodes, compared against our standard 2D electrode due to differences in the overpotentials. Thus, demonstrating our 3D printed electrodes can surpass the constraints linked to mass transport in thick electrodes, as we have now changed the kinetics at the electrode surface. Overall, we have achieved a multi-disciplinary project as we are discovering new electrode manufacturing processes, whilst using a Na-ion material to create the next-generation of batteries. Figure 1

Inductive Behavior in Electrochemical Impedance Spectroscopy: Can We Discriminate between Adsorption and Non-Stationarity

Electrochemical impedance spectroscopy (EIS) is a widely used technique for studying electrochemical processes. EIS typically assumes a linear relationship between the applied signal (potential or current) and the measured response (current or potential). In other words, doubling the input perturbation must result in doubling the output, and the output signal must show no change in shape. However, by using “small input signals”, a linear response can be achieved. Similarly, stationarity is also a requirement for EIS measurements. In this case, several factors may be at the origin of the problem. For instance, as an electrochemical reaction progresses, the electrode surface and the surrounding electrolyte can change, affecting the resistance and capacitance, and consequently, the impedance. Temperature variations can also affect the conductivity and mobility of ions, leading to a shift in impedance as a function of the frequency. If a system is non-stationary during an impedance measurement, the measured value won't represent a single, fixed state. The impedance will depend on the time the measurement was taken. This can make it difficult to interpret the data and compare it with other measurements. Conversely, reaction mechanism involving adsorbates may be misinterpreted. Indeed, adsorption processes can result in either capacitive or inductive time-constants, usually observed in the low frequency domain. Such a behavior has been reported in the literature for corrosion processes. In this presentation, we will show how non-stationarity can modify an impedance diagram. Particular attention will then be paid to the case of the response of an adsorbed intermediate, such as the corrosion of Mg, for which inductive feature can be observed. The importance of the Kramers-Kronig relationships will then be discussed.

Dependence of Cation Structures on Electrochemical Polymerization of Aniline in Phosphonium Ionic Liquids

Ionic liquids (ILs) are known to possess unique physicochemical and abundant design properties. When ILs are used as electrolytes in the electropolymerization reactions of aromatic compounds to form conducting polymers, the grown film properties are significantly dependent of the combination of cations and anions. Typical researches on the IL-based electrolytes have been described for nitrogen-based ILs;1) on the other hand, phosphonium-based ILs have also attracted attention in recent years. We have reported the preliminary electrochemical investigation for electropolymerization of aniline (ANi), indicating that the phosphonium ILs were able to be employed as potential electrolytes.2) In this work, various phosphonium ILs ( Fig. 1) including typical two phosphonium ILs such as triethylpenthylphosphonium bis(trifluoromethanesulfonyl)amide (P2225-TFSA) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)amide (P4441-TFSA) 3) are selected for the electrooxidative polymerization of ANi, in order to investigate the influence of the physicochemical properties of the phosphonium ILs on the electropolymerization processes and the grown polyaniline (PANi) films.The phosphonium ILs were synthesized and purified according to a previously published paper.3) The electrolytes were prepared by adding 2.0 M of ANi monomer and 1.0 M of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA) as a proton source. The electropolymerization was carried out by cyclic voltammetry (CV) using a three-electrode cell with a platinum disc or an indium tin oxide (ITO) as a working electrode, a Ag/Ag+ as a reference electrode and a platinum wire as a counter electrode (potential sweep rate: 0.1 V s-1, potential range: -0.5~+1.5 V). The morphology of the electropolymerized PANi films on the ITO electrode were observed by scanning electron microscopy (SEM).Fig. 2 shows the cyclic voltammograms for electrooxidative polymerization of ANi in typical P2225-TFSA and P4441-TFSA. It was found that the P4441-TFSA based electrolyte tended to give relatively low oxidation currents, forming the uniform PANi film on the electrode surface as shown in Fig. 3. The voltammograms for the electropolymerization measured in various phosphonium ILs will be discussed, demonstrating the influence of the transport property of the phosphonium IL electrolytes.

Development of an In Vivo, Real-Time and Continuous Insulin Sensor Utilizing an Extended Gate Field Effect Transistor-Based Transducer

Introduction In this paper, we aim to utilize an extended gate field-effect transistor (EGFET)-based transducer to measure insulin. The design of EGFETs is characterized by a unique structural arrangement, where a physical barrier exists between the semiconductor component and the analyte or physical medium. Due to this structure, EGFET possesses the advantage of protecting the electrode from intricacies within the measurement solution or medium. The need for a redox probe is also effectively eliminated by incorporating EGFETs, marking a significant breakthrough in electrochemical measurement. The lack of a redox probe allows EGFET-based sensors to conduct measurements with minimal invasiveness and enhanced biocompatibility in accordance with an in vivo monitoring system. As the target analyte is not required to be electrochemically active, EGFET is highly customizable for a wide range of targets, including neurotransmitters, biomarkers, and metabolites. Therefore, we constructed immunosensors immobilized with anti-insulin single-chain antibody (scFv) and measured insulin levels, with the objective of creating an in vivo sensor designed to improve glycemic management. We aimed to implement the inherent semiconductor properties of EGFETs by performing real-time monitoring of changes in electrical properties to quantify various insulin concentrations. Methods Development of an in vivo sensor requires the use of a platform that can be implemented within an in vivo environment. For this purpose, we utilized a gold microwire electrode immobilized with anti-insulin scFv. The gold microwire electrodes were prepared by electrochemically cleaning and further roughening them to increase the active surface area for the purpose of improving immobilization of the antibody. To achieve site-specific immobilization of anti-insulin scFv, we employed a nickel-chelated nitrilotriacetate self-assembled monolayer (Ni-NTA SAM). As the scFv harbors a histidine tag and Ni-NTA has an affinity for histidine residues, we were able to achieve oriented immobilization on the electrode surface. Within this study, we compared the effects of covalent immobilization, which leads to random orientation with the antibody, and non-covalent oriented immobilization by comparing the signal obtained from EGFET measurement. EGFET measurements were conducted using a transistor consisting of source, drain, and gate terminals. In this configuration, a constant potential was maintained between the source and drain terminals, while a sweeping potential was applied between an Ag/AgCl reference electrode and the source terminal. Measurement of insulin was performed within a buffer and artificial interstitial fluid (aISF) to model an in vivo environment. Results and Discussion The interaction between insulin and the immobilized anti-insulin scFv on the electrode surface induces a shift in surface potential, driven by the redistribution of charges across the extended gate. The change in surface potential leads to a subsequent modification of the gate potential, known as Vg. The gate potential, when less than the threshold voltage (Vth), operates in the cutoff region where little to no current is present. However, when Vg is greater than Vth, the system operates in the ohmic region where current can flow. The following relationship allowed us to monitor the drain-source current or Ids within the ohmic region to evaluate insulin concentrations. The signal change due to insulin binding to anti-insulin scFv was observed at a reference voltage of 0.6 volts. Conclusion We measured insulin concentrations using an electrode modified with anti-insulin scFv and demonstrated that EGFET can be used as a working principle for an in vivo monitoring system. Additionally, the measurement principle does not require a redox probe within the measurement solution. Future work will include implanting the anti-insulin scFv immobilized gold microwire electrode within a rat model and measuring insulin.