Quasi-reference Electrode Research Articles

Novel integrated reference-counter electrode for electrochemical measurements of HOMO and LUMO levels in small-molecule thin-film semiconductors for OLEDs

Organic light-emitting diodes (OLEDs) are a prominent display technology, yet the accurate characterization of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels in their constituent materials remains challenging. This study introduces a novel integrated reference-counter electrode (IRCE) assembly, leveraging a gel polymer electrolyte with an embedded silver quasi-reference electrode, facilitating the electrochemical measurement of HOMO and LUMO levels in small molecular thin-film semiconductors. Calibration of the IRCE against ferrocene enables the establishment of an absolute energy scale. Comparative stability tests against a standard Ag/AgNO3 reference electrode confirm the IRCE's reliability. Electrochemical characterization using cyclic voltammetry was performed on prototypical OLED materials, including NPB, TCTA, PO-T2T neat films, and an NPB:PO-T2T exciplex film. While NPB and PO-T2T exhibited stable voltammograms, TCTA showed signs of electropolymerization. Additionally, the HOMO level of the NPB:PO-T2T exciplex was slightly shifted compared to that of NPB, suggesting interactions within the exciplex. The results demonstrated the IRCE's capability to accurately determine frontier energy levels in thin films, paving the way for better device modeling and a better understanding of underlying electronic processes in organic semiconductors.

Ion sensors based on organic semiconductors acting as quasi-reference electrodes

Thin-film devices that transduce the chemical activity of ions into electronic signals are essential components in various applications, including healthcare diagnostics and environmental monitoring. Combinations of organic semiconductors (OSCs) and ion-selective materials have been explored for developing solution-processable ion sensors. However, the necessity of reference electrodes (REs) and operational stability in ion-permeable OSCs have posed questions regarding whether reliable measurements with thin-film components are attainable with OSCs. Herein, we report electric double-layer transistors (EDLTs) with OSCs in single-crystal forms for ion sensing. Our EDLTs demonstrated high operational stability, with a one-to-one relationship between the source electrode potential and device resistance, and served as quasi-REs (qRE). When our EDLT is served as qRE, its drift was as small as 0.5 mV/h and comparable to that of commonly employed REs. In our system, the semiconductor-electrolyte interface is self-passivated by the alkyl chains of OSCs in single-crystal structures, with the two-dimensional transport layer appearing unaltered upon gating. EDLT arrays with ion-selective and nonselective liquid junctions enable ion concentration sensing without a conventional RE. These findings provide opportunities to develop thin-film devices based on OSCs for easy integration and reliable measurements.

Ultradense Array of On-Chip Sensors for High-Throughput Electrochemical Analyses.

High-throughput sensors are valuable tools for enabling massive, fast, and accurate diagnostics. To yield this type of electrochemical device in a simple and low-cost way, high-density arrays of vertical gold thin-film microelectrode-based sensors are demonstrated, leading to the rapid and serial interrogation of dozens of samples (10 μL droplets). Based on 16 working ultramicroelectrodes (UMEs) and 3 quasi-reference electrodes (QREs), a total of 48 sensors were engineered in a 3D crossbar arrangement that devised a low number of conductive lines. By exploiting this design, a compact chip (75 × 35 mm) can enable performing 16 sequential analyses without intersensor interferences by dropping one sample per UME finger. In practice, the electrical connection to the sensors was achieved by simply switching the contact among WE adjacent fingers. Importantly, a short analysis time was ensured by interrogating the UMEs with chronoamperometry or square wave voltammetry using a low-cost and hand-held one-channel potentiostat. As a proof of concept, the detection of Staphylococcus aureus in 15 samples was performed within 14 min (20 min incubation and 225 s reading). Additionally, the implementation of peptide-tethered immunosensors in these chips allowed the screening of COVID-19 from patient serum samples with 100% accuracy. Our experiments also revealed that dispensing additional droplets on the array (in certain patterns) results in the overestimation of the faradaic current signals, a phenomenon referred to as crosstalk. To address this interference, a set of analyses was conducted to design a corrective strategy that boosted the testing capacity by allowing using all on-chip sensors to address subsequent analyses (i.e., 48 samples simultaneously dispensed on the chip). This strategy only required grounding the unused rows of QRE and can be broadly adopted to develop high-throughput UME-based sensors. In practice, we could analyze 48 droplets (with [Fe(CN)6]4-) within ∼8 min using amperometry.

Understanding Lithium-Gold Electrochemical Reactions Using Operando X-Ray Diffraction

Gold electrodes are used in lithium-based battery research as catalysts and micro / quasi-reference electrodes despite their high cost and unclear reactivity with lithium. Here we present an investigation of the electrochemical reactions of gold-lithium (Au-Li) mixtures using variable-temperature electrochemistry and operando X-ray diffraction.Multiple solid solutions (alpha, beta, delta) and intermetallic phases (AuLi3, Au4Li15) are expected based on the equilibrium phase diagram.1 Previous electrochemical investigations conclusively identified only AuLi3;2,3 alpha and beta may be bypassed during lithium insertion, and the structure of delta is unclear.4 We are unaware of any previous reports of the electrochemical formation of Au4Li15. Metastable crystallographic solutions have been proposed.5 X-ray diffraction patterns collected during the galvanostatic lithiation of gold leaf (at 60 °C and a rate of ca. C/50) are provided in Figure 1. Reference diffraction patterns and the associated Powder Diffraction File card number are indicated, along with proposed phases.4,5 X-ray and electrochemical data align with earlier results suggesting that the equilibrium alpha and beta phases are seemingly bypassed during the first insertion. Delta is the first phase to form at a potential of 0.25 V vs. Li/Li+, followed by the formation of AuLi3 at 0.15 V vs. Li/Li+ at all conditions and Au4Li15 at 0.05 V vs. Li/Li+ in select conditions. Electrochemical data suggests AuLi3 may also have a small range of solubility. Peaks associated with AuLi3 and Au4Li15 align with existing literature but peaks associated with delta do not. Reactions are reversible to delta, followed by the formation of another phase near 0.3 V vs. Li/Li+ and alpha at potentials above 0.4 V vs. Li/Li+ during lithium removal. Significant hysteresis is present in cell potential and reaction pathways in the low-lithium content region. The second cycle (not shown) is reversible between alpha (not pure gold) and the terminal phase without a significant loss in capacity. Alternative crystallographic unit cell(s) for delta and other gold-lithium phases will be described.While the delta / AuLi3 reaction exhibited a consistent potential during lithium insertion and removal, the potential otherwise varied strongly with temperature, rate, and composition, implying that gold quasi-reference electrodes may not be suitable for lithium-ion battery research.

Investigation of High-Sensitivity pH Sensor Based on Au-Gated AlGaN/GaN Heterostructure

A high-sensitivity pH sensor based on an AlGaN/GaN high-electron mobility transistor (HEMT) with a 10 nm thick Au-gated sensing membrane was investigated. The Au nanolayer as a sensing membrane was deposited by electron-beam evaporation and patterned onto the GaN cap layer, which provides more surface-active sites and a more robust adsorption capacity for hydrogen ions (H+) and hydroxide ions (OH−) and thus the sensitivity of the sensor can be significantly enhanced. A quasi-reference electrode was used to minimize the sensing system for the measurement of the microliter solution. The measurement and analysis results demonstrate that the fabricated sensor exhibits a high potential sensitivity of 58.59 mV/pH, which is very close to the Nernstian limit. The current sensitivity is as high as 372.37 μA/pH in the pH range from 4.0 to 9.18, under a 3.5 V drain-source voltage and a 0 V reference-source voltage. Comparison experiments show that the current sensitivity of the Au-gated sensor can reach 3.9 times that of the SiO2-gated sensor. Dynamic titration experiments reveal the pH sensor’s ability to promptly respond to immediate pH variations. These findings indicate that this pH sensor can meet most application requirements for advanced medical and chemical analysis.

Electrochemical H2O2 Production Modelling for an Electrochemical Bandage

Hydrogen peroxide (H2O2) is an environmentally friendly oxidizing agent used to treat wound infections. We have developed an electrochemical bandage (e-bandage), which generates H2O2 in situ and shown that it exhibites in vitro and in vivo efficacy. The electrochemical bandage comprises carbon fabric working and counter electrodes, as well as an Ag/AgCl quasi-reference electrode, separated by cotton fabric and the electrolyte is delivered by Xanthan gum with phosphate buffer saline. While the chemistry and electrochemistry of the e-bandage have been experimentally characterized, the system level description could aid in better designing these devices. Here, a model called electrochemical hydrogen peroxide production (EHPP) was used to evaluate factors influencing electrochemical generation of H2O2, including electrode potential, diffusion and reaction rates, temperature, and various geometries. EHPP model parameters estimated based on experimental results indicate that: (i) with diffusion limitations caused by changes in physical conditions (e.g., drying of hydrogel), the rate of H2O2 generation decreases, (ii) higher working electrode overpotentials increase H2O2 generation and higher counter electrode overpotentials do not affect H2O2 generation, (iii) increasing the distance between electrodes by adding more hydrogel reduces H2O2 generation, (iv) net H2O2 generation decreases ∼12% with temperature, and (v) H2O2 production is most effective in the initial 48 h of operation.

Reference Electrode Types for Zero-Gap CO2 Electrolyzers: Benefits and Limitations.

Integrated reference electrodes allow to deconvolute voltage contributions of anode and cathode and contribute to a better understanding of CO2 electrolyzers. However, in zero-gap cell configurations, this integration can be challenging and obtaining error-free data with such a setup is a non-trivial task. This study compares five different methods to integrate a reference electrode into an alkaline zero-gap CO2 electrolysis cell. Sources of error and measures to circumvent them are investigated and finite-element simulation is used to gain a better understanding of observed effects. Placing a reference electrode into the inactive area of the cell is found to be a reliable method, as long as the placement of electrodes is sufficiently controlled. Sandwiching a wire quasi-reference electrode between two membranes is especially useful for electrochemical impedance spectroscopy; however, it can affect the overall cell performance. Contacting the catalyst layer from the backside with a salt-bridge is promising for localized measurements if sufficient reproducibility can be ensured.

A sensitive and selective voltammetric method for the detection of pyrogallol in tomato and water samples using platinum electrode modified with alizarin red S film.

In contrast to the hyperactive platinum electrode, ARS modified platinum electrode presents a remarkable inertness toward adsorption and surface processes and lends it for further voltammetric applications. Measuring pyrogallol levels in samples is significant for assessing their antioxidant activity, which is crucial for understanding their potential health benefits and ability to combat oxidative stress. In addition, the excess consumption of pyrogallol can have significant negative effects on human health. A voltammetric sensor has been developed for the determination of pyrogallol using ARS modified platinum electrode. The electrode was prepared by electrodeposition of alizarin red S on a platinum electrode using cyclic voltammetry with a potential scan range of - 0.4 to 1.2V against an Ag/AgCl quasi reference electrode for 60 cycles as optimum number of cycles. The modified electrode was characterized by CV and SEM techniques. This modified alizarin red S platinum electrode showed remarkable electrocatalytic performance and stability, resulting in a significant increase in pyrogallol oxidation current by 11.05% compared to the pyrogallol oxidative current at the unmodified platinum electrode. A well-defined oxidation peak was observed at ~ 0.40V. The sensor exhibited a low limit of detection (LOD) of 0.28µM and a linear standard curve covering the ranges of 1.0-40µM and 0.01-10.0mM pyrogallol. Extensive studies were performed to evaluate possible interferences from various organic and inorganic compounds and yielded satisfactory results that confirm the selectivity of the developed sensor for pyrogallol determination. In addition, the ARS-Pt electrode provided consistently reliable results for the accurate detection of pyrogallol in water and tomato samples.

Lithium-Gold Electrochemical Alloying: Clarifying Reaction Pathways and Products Using Operando XRD

Gold electrodes are used in lithium-ion battery research despite their high cost and unclear reactivity with lithium. Many equilibrium phases of gold-lithium (Au-Li) exist—solid solutions alpha, beta, and delta, and intermetallic phases AuLi3 and Au4Li15. During the first alloying reaction, the equilibrium alpha and beta phases are seemingly bypassed; a phase, presumably delta, forms at a potential of 0.25 V (all potentials vs Li/Li+), followed by the formation of AuLi3 at 0.15 V at all conditions tested and Au4Li15 at 0.05 V in select conditions. Alloying reactions are reversible to (delta), followed by the formation of another phase near 0.3 V and a low Li content phase at potentials above 0.4 V during de-alloying. Observed diffraction peaks only partially align with previous reports for all phases other than Au4Li15. The second alloying/de-alloying cycle is reversible between a low Li content phase (not pure gold) and the terminal phase. Some reaction hysteresis is present at low Li content. While the (delta)/AuLi3 reaction had a consistent potential during alloying and de-alloying, the potential otherwise varied strongly with temperature, rate, and composition, implying that gold quasi-reference electrodes may not be suitable for lithium-ion battery research.

Single-Response Duplexing of Electrochemical Label-Free Biosensor from the Same Tag.

Multiplexing is a valuable strategy to boost throughput and improve clinical accuracy. Exploiting the vertical, meshed design of reproducible and low-cost ultra-dense electrochemical chips, the unprecedented single-response multiplexing of typical label-free biosensors is reported. Using a cheap, handheld one-channel workstation and a single redox probe, that is, ferro/ferricyanide, the recognition events taking place on two spatially resolved locations of the same working electrode can be tracked along a single voltammetry scan by collecting the electrochemical signatures of the probe in relation to different quasi-reference electrodes, Au (0V) and Ag/AgCl ink (+0.2V). This spatial isolation prevents crosstalk between the redox tags and interferences over functionalization and binding steps, representing an advantage over the existing non-spatially resolved single-response multiplex strategies. As proof of concept, peptide-tethered immunosensors are demonstrated to provide the duplex detection of COVID-19 antibodies, thereby doubling the throughput while achieving 100% accuracy in serum samples. The approach is envisioned to enable broad applications in high-throughput and multi-analyte platforms, as it can be tailored to other biosensing devices and formats.

Fabrication of a polishable and reusable triple electrode as a new generation of three-electrode systems for the electrochemical analysis applications through both immersion and drop casting-procedures

An innovative three-electrode system was developed for electrochemical analysis, aiming to overcome the limitations of conventional approaches. The system incorporates a glassy carbon rod as the working electrode, platinum wire as the counter electrode, and silver wire as the quasi-reference electrode that are positioned within an epoxy resin substrate. The advantages of this type of three-electrode system include the possibility of sample analysis in both drop mode and when immersed in the solution, low manufacturing cost, reduction of chemical consumption, no need for special maintenance protocols, no requirement for stand, absence of liquid junction potential (due to the direct contact of the reference electrode with the solution), usability for on-site analysis, and usability for non-aqueous solutions.To check the efficiency of this electrode, cyclic voltammetry technique was used. Also, for direct comparison of PTE with conventional three-electrode system and screen-printed electrode (SPE), current density was used instead of peak current. According to the results, PTE system shows more peak current for the same surface area of the working electrode compared to other systems, which shows the high efficiency of the proposed system for electrochemical analysis. Acetaminophen (ACT) was chosen in order to investigate the ability to measure an analyte with PTE using differential pulse voltammetry (DPV). The linear range was obtained from 29.12 μM to 609.37 μM with a detection limit (LOD) 20.22 μM. Also, PTE was used to measure ACT in tablet as real sample.

An electroplated Ag/AgCl quasi-reference electrode based on CMOS top-metal for electrochemical sensing

The integration and mass-production of reference electrodes for CMOS-based electrochemical sensing systems pose a challenge for the accessibility and commercial-viability of such devices. In this paper, a method of electroplating an Ag/AgCl quasi-reference electrode using CMOS top-metal as a base is presented for the first time. The aluminium bond-pad of a CMOS microchip was zincated, an electroless nickel immersion gold layer applied, and a thick silver layer electroplated and chemically chlorinated. The resulting reference electrode was able to provide a stable potential with a drift rate of 0.3mV/h for up to 18h. This validates the approach of a fully electroplated bond-pad reference electrode, which offers simplified post-processing and greater scalability of production. Further work towards an entirely electroless process is envisaged.

Impedance Spectroscopy with Microscopic Reference Electrodes as a Technique to Study Electrode Kinetics in Dye-Sensitized Solar Cells

Measurements with microscopic reference electrodes in electrochemical impedance spectroscopy (µRE-EIS) were used to study electrode kinetics of dye-sensitized solar cells (DSSCs). A detailed impedance analysis of DSSCs is essential to separately optimize different rate-determining steps in these cells. Two-electrode measurements as typically used, however, often do not allow a separate analysis of charge transfer reactions at different electrodes that occur with similar time constants. Such problems, e.g., arise in DSSCs with water-based electrolytes using 2,2,6,6-tretramethylpiperidine-1-oxyl (TEMPO) as a redox mediator. The use of a quasi-reference electrode offers the possibility to separately record impedance spectra of the photoanode and the counter electrode of a DSSC under operating conditions in one experiment. With this method, electron transfer kinetics could be studied for both electrodes individually and contributions of charge carrier recombination at the photoanode could be studied separately from the reduction of the redox mediator at the counter electrode.In DSSCs, the sensitized photoanode and the counter electrode are commonly separated by no more than 60 µm, depending on the thickness of the sealing foil. Into such an arrangement, a thin platinum wire was introduced as a third electrode, serving as a microscopic quasi-reference electrode (µRE). The architecture was adjusted stepwise and the influence of the adjustments was studied to ensure that important cell properties such as solar cell parameters and diffusion resistance remained comparable to cells in a typical two-electrode architecture.Subsequently, three-electrode experiments were carried out, using the photoanode as the working electrode (WE), a counter electrode (CE), and the µRE. For µRE-EIS experiments, the potential was modulated between CE and WE and the overall cell impedance Z 0 was determined. Simultaneously, the impedance between µRE and WE was recorded (Z 1) and the impedance between µRE and CE (Z 2) was calculated from Z 0 and Z 1. Thus, one experiment yielded spectra for the full cell and both respective half-cells WE vs. µRE and CE vs. µRE.Here, we investigated DSSCs based on TiO2 photoanodes sensitized with the organic dye Y123, aqueous electrolytes with the organic redox mediators TEMPO+/0 or OH-TEMPO+/0, and poly(3,4-ethylenedioxythiphene) (PEDOT) counter electrodes. The impedance spectra revealed that there are contributions in the same frequency range in both half-cell spectra, suggesting that both charge transfer processes from the electrodes to the oxidized redox species, i.e., recombination at the photoanode and the reduction of the redox mediators at the counter electrode, respectively, occur on similar time scales. These contributions superimpose in a typical two-electrode measurement and cannot be separated. µRE-EIS, however, proved to be a powerful tool to simultaneously study the interactions of novel redox mediators with photoanodes and counter electrode materials in detail. Figure 1

Determination of dopamine in blood serum and urine samples by differential pulse voltammetry at an iodine-coated platinum electrode

While platinum electrode shows hyperactivity towards adsorption and surface processes, iodine-coated platinum electrode offers remarkable inertness toward them. Therefore, iodine-coated platinum electrodes lend themselves to probe chemical species in the bulk solution without intervention from adsorption and surface processes. The current work presents utilization of iodine-coated polycrystalline platinum electrode as a voltammetric sensor for determination of dopamine in serum and urine samples. Differential pulse voltammetry (DPV) at iodine coated polycrystalline platinum electrode is the technique of choice whenever higher sensitivity is sought. DPV with a scan rate of 5 mV/s was applied for determination of dopamine in PBS at pH 7. The anodic peak related to dopamine oxidation in the above-mentioned solution was centered at ~0.1V vs. Ag/AgCl quasi reference electrode. The linear range for the developed method was between 1.0 and 100 µM. The anodic peak current showed excellent linearity with dopamine concentration (R2 =0.9977) over the above-mentioned range. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.29 µM and 0.96 µM respectively which attests to the high sensitivity of the developed method. The proposed method was successfully applied to the analysis of dopamine in serum and urine samples. The percent recovery values ranged from 94.4 to 104.5% attesting to the accuracy of the developed method and absence of determinate errors.

EFFECT OF THE SUBSTRATE MATERIAL ON THE KINETICS OF SILICON ELECTROREDUCTION IN THE KCl–CsCl–K<sub>2</sub>SiF<sub>6</sub> MELT

Due to the possibility of controlling composition and morphology, one of the promising methods for obtaining silicon and its materials is the electrolysis of molten salts. However, this requires data on the influence of various factors on the kinetics of silicon electrodeposition. In this work, an effect of the cathode substrate material on the kinetics of electroreduction of silicon ions in a low-fluoride melt (wt %) 57KCl–43CsCl with the addition of 2.8 wt % K2SiF6 at a temperature of 730°C was studied by cyclic voltammetry and chronoamperometry. Interacting and indifferent materials for silicon were chosen as substrates: glassy carbon, silver, and nickel. On the glassy carbon electrode, the electroreduction of silicon ions proceeds in the potential region more negative than –0.05 V, on the silver electrode, more negative than 0.05 V, and on the nickel electrode, more negative than 0.40 V relative to the potential of the silicon quasi-reference electrode. For all the studied substrates, a cathode process is observed, which is not electrochemically reversible. In this case, according to chronoamperometry measurements, the stage of nucleation of a new phase at the cathode does not affect the kinetics of the process under study. Presumably, in the case of glassy carbon and silver, irreversibility can be caused by a delayed discharge, while silicon electrodeposition on a nickel electrode is accompanied by the formation of nickel silicides. From the voltammetric and chronoamperometric dependences, the diffusion coefficient of silicon ions to the glassy carbon electrode was estimated, the values of which were 1.5 · 10–5 and 1.2 · 10–5 cm2/s, respectively.

Laser induced graphene electrochemical aptasensor based on tetrahedral DNA for ultrasensitive on-site detection of microcystin-LR

The development of accurate and reliable sensor for on-site detection of microcystin-LR (MC-LR), one of hazardous environmental pollutants, is highly required. Herein, a laser induced graphene (LIG)-based electrochemical aptasensor for sensitive on-site detection of MC-LR was reported. LIG electrode, the substrate of aptasensor, was prepared via thermal transfer with ethylene-vinyl acetate copolymer, and LIG acted as quasi-reference electrode to replace conventional Ag/AgCl electrode for better operability and robustness. LIG electrode provided large surface area to assemble tetrahedral DNA to absorb methylene blue (MB) for the signal amplification. For detection, the specific recognition of MC-LR with aptamer led to the stripping of tetrahedral DNA complex and further the decreased redox current of MB (IMB). Consequently, the fabricated aptasensor offered high analytical performance for MC-LR detection with a linear range of 1 × 10-2-1 × 105 pM and a detection limit of 3 × 10-3 pM, which was successfully used for water sample analysis with comparable reliability and accuracy of standard method. Furthermore, a portable detection platform by coupling of LIG-based electrochemical aptasensor with electrochemical workstation was constructed for on-site detection of MC-LR. This work offers a novel method for the on-site monitoring of MC-LR, which promotes the investigation of LIG-based electrochemical biosensing in the field of environmental analysis.

Miniaturized Chip Integrated Ecological Sensor for the Quantitation of Milnacipran Hydrochloride in the Presence of Its Impurities in Dosage Form and Human Plasma

The sensitivity and selectivity of potentiometric sensors towards their targets in various matrices have been challenging for analysts since their development. Modifications of the sensor composition provide the sensitivity and selectivity of potentiometric sensors towards their targets in various matrices have been challenging for analysts since their development. Modifications of the sensor composition provide a way to achieve the utmost sensitivity and selectivity. Molecular imprinting, together with conducting polymers and graphite derivatives, represents a robust composite that attains better sensor performance. Besides, the miniaturization of potentiometric sensors is advantageous to the sensitivity and greenness of the developed sensors due to their smaller portable size, lower sample volume, and lower waste. These advantages provide these sensors with a fast track toward developing wearable versions of ion-selective sensors, which are valuable in point-of-care services in different clinical settings. Here, we report on the first recyclable on-chip miniaturized potentiometric sensors integrated by a printed Ag/AgCl quasi-reference electrode for the quantitation of milnacipran hydrochloride (MLN) in its dosage form and human plasma in the presence of its impurities. The sensing module of the sensor is modified by a molecularly imprinted conducting polymer (polyaniline), which is computationally optimized to achieve maximum selectivity towards MLN in the presence of its impurities. Moreover, the designated sensor composition is optimized by a self-validated ensemble modeling experimental design seeking the composition leading to optimal sensor performance. The proposed on-chip sensor successfully achieved a LOD value of (7.94 × 10−7 M) and a linear range of (1 × 10−6 − 1 × 10−2 M) with a green analytical profile as redeemed from the Agree assessment score.

In Situ Polymerization Synthesis of Graphdiyne Nanosheets as Electrode Material and Its Application in NMR Spectroelectrochemistry.

In situ NMR spectroelectrochemistry is extremely powerful in studying redox reactions in real time and identifying unstable reaction intermediates. In this paper, in situ polymerization synthesis of ultrathin graphdiyne (GDY) nanosheets was realized on the surface of copper nanoflower/copper foam (nano-Cu/Cuf)-based electrode with hexakisbenzene monomers and pyridine. Palladium (Pd) nanoparticles were further deposited onto the GDY nanosheets by the constant potential method. By using this GDY composite as electrode material, a new NMR-electrochemical cell was designed for in situ NMR spectroelectrochemistry measurement. The three-electrode electrochemical system consists of a Pd/GDY/nano-Cu/Cuf electrode as the working electrode, a platinum wire as the counter electrode, and a silver/silver chloride (Ag/AgCl) wire as a quasi-reference electrode, which can be dipped into a specially constructed sample tube and adapted for convenient operation in any commercial high-field, variable-temperature FT NMR spectrometer. The application of this NMR-electrochemical cell is illustrated by monitoring the progressive oxidation of hydroquinone to benzoquinone by controlled-potential electrolysis in aqueous solution.

Expanding the possibilities for an instrument-free method to reproducible resetting of the standard potential (E°) of solid-contact ion-selective electrodes

Improving the reproducibility of the standard potential (E°) of solid-contact ion-selective electrodes (SC-ISEs) is of utmost importance on the way to simpler measurements with disposable sensors and sensors in locations where maintenance is challenging. In this work, an earlier introduced instrument-free method to reset the E° to a specific potential is developed by short-circuiting SC-ISEs with a solid-state Ag/AgCl quasi reference electrode (QRE) in a certain concentration of chloride and the primary ion of the SC-ISE. The short-circuiting method is evaluated for SC-ISEs based on poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs) as solid contacts, while a typical valinomycin-based spin-coated K+-selective membrane is used as a model ion-selective membrane. The capacitance of the Ag/AgCl QRE used in this work is orders of magnitude larger than the capacitance of the solid contact of the studied SC-ISEs. Therefore, upon short-circuiting, the potential of the QRE remains practically constant, while the potential of the SC-ISE is shifted until the potential difference between the SC-ISE and QRE approaches zero. When short-circuiting the SC-ISE with an Ag/AgCl QRE, the calibration curves can be shifted reversibly up and down on the potential axis in a reproducible and controlled manner. The calibration curve can be shifted by applying current pulse on SC-ISEs.

Autonomous electrochemical system for ammonia oxidation reaction measurements at the International Space Station

An autonomous electrochemical system prototype for ammonia oxidation reaction (AOR) measurements was efficiently done inside a 4'' x 4'' x 8'' 2U Nanoracks module at the International Space Station (ISS). This device, the Ammonia Electrooxidation Lab at the ISS (AELISS), included an autonomous electrochemical system that complied with NASA ISS nondisclosure agreements, power, safety, security, size constrain, and material compatibility established for space missions. The integrated autonomous electrochemical system was tested on-ground and deployed to the International Space Station as a “proof-of-concept” ammonia oxidation reaction testing space device. Here are discussed the results of cyclic voltammetry and chronoamperometry measurements done at the ISS with a commercially available channel flow-cell with eight screen-printed electrodes, including Ag quasi-reference (Ag QRE) and carbon counter electrodes. Pt nanocubes in Carbon Vulcan XC-72R were used as the catalyst for the AOR and 2 μL drop of Pt nanocubes/ Carbon Vulcan XC-72R, 20 wt%, ink was placed on the carbon working electrodes and allowed to dry in air. After the AELISS was prepared for launch to the ISS, a 4 days delayed (2 days in the space vehicle Antares and 2 days space transit to the ISS) cause a slight shift on the Ag QRE potential. Nevertheless, the AOR cyclic voltametric peak was observed in the ISS and showed ca. 70% current density decrease due to the buoyancy effect in agreement with previous microgravity experiments done at the zero-g aircraft.