Reference Electrode Research Articles

Degradation of iron‐nickel alloy interconnects in contact with lanthanum nickelates based double‐layer electrodes during long‐term tests

AbstractThis paper focuses on long‐term tests held during 1,000 h on different Membrane‐Electrode‐Interconnect Assemblies (MEIAs), consisting of an Fe‐Ni alloy interconnect and an electrochemical cell based on a Ce0.8Sm0.2O2–δ electrolyte, the double‐layer working electrode with a La2NiO4 + δ – Ce0.8Sm0.2O2–δ composite functional layer, and a LaNi0.6Fe0.4O3–δ current collector layer, and a platinum reference electrode (O2, LaNi0.6Fe0.4O3–δ|La2NiO4 + δ – Ce0.8Sm0.2O2–δ|Ce0.8Sm0.2O2–δ|Pt, O2). These tests were carried out on MEIAs with the Cr‐free 47ND alloy of the Fe–Ni system with and without surface modification at 850°C in air. The electrochemical performance of MEIAs was studied without polarization as well as under cathodic and anodic polarization with current density 0.5 A cm−2 by means of electrochemical impedance spectroscopy (EIS). The mechanism of the MEIA evolution during long‐term test is discussed.

PERFORMANCE ENHANCEMENT OF BRASS EDM ELECTRODES WITH CRYOGENIC TREATMENT WHILE MACHINING THE COLD WORK STEEL AISI D2

This study investigates the performance of deep cryogenically treated brass (CuZn25Al5) electrodes in the die-sink EDM process. Two different cryogenic treatment durations, 6 h and 12 h, were applied to 8 mm diameter electrodes, and their effects were compared to untreated electrodes. The machining tests were conducted under moderate and aggressive conditions. In the machining tests, the 6-h cryo-treated electrode exhibited a 16.8% increase in material removal rate (MRR) under moderate conditions and a 19.7% increase under aggressive conditions compared to the reference electrode. The 12-h cryo-treated electrode showed similar MRR values to the reference electrode but improved tool wear resistance by 9.4% under moderate conditions. The kerf angle was minimized, indicating better hole verticality, in the 6-h cryo-treated electrode group. The improvement in machining performance was attributed to the enhancement in electrical conductivity of the electrodes, which increased by 28% for the 6-h cryo-treated electrode and 20% for the 12-h cryo-treated electrode. X-ray diffraction (XRD) analysis revealed shifts in peak positions and possible phase transformations due to cryogenic treatment. Surface roughness measurements showed improved surface conditions in the cryo-treated electrodes under aggressive conditions. The results indicate that cryogenic treatment enhances MRR, reduces tool wear, and improves surface quality in die-sink EDM. These improvements are attributed to increased electrical conductivity and changes in the internal structure of the brass electrode.

Research on Quantitative Diagnosis of Dendrites Based on Titration Gas Chromatography Technology

Lithium plating can cause capacity fade and thermal runaway safety issues in lithium-ion batteries. Therefore, accurately detecting the amount of lithium plating on the surface of the battery’s negative electrode is crucial for battery safety. This is especially crucial in high-energy-density applications such as battery energy storage systems or in electric vehicles (EVs). Early detection of lithium plating is crucial for evaluation of reliability and longevity. It also serves as a method for early diagnostics in practical industrial applications or infrastructure, such as EV transportation. This can enhance its impact on customers. This study validates the effectiveness of titration gas chromatography (TGC) technology in quantitatively detecting lithium plating on graphite negative electrodes in lithium-ion batteries. The results show that it can detect a minimum of 2.4 μmol of metallic lithium. Compared with the heating direct current resistance and reference electrode methods, which can be used to perform only qualitative dendrite detection, TGC has a wider range of detection. Compared with the nuclear magnetic resonance (NMR) method with higher quantitative detection accuracy, the maximum difference between the detection results of the two methods was only 7.2%, but the TGC method had lower cost and higher implementation convenience. In summary, among various dendrite detection methods, the TGC method can not only realize the effective quantitative detection of lithium plating, but also comprehensively consider its detection range, implementation convenience, cost, and detection accuracy, indicating that it is suitable for engineering applications and has the prospect of realizing large-scale quantitative detection of lithium plating in lithium-ion batteries.

The Development of a Stable and Practical Saturated Reference Electrode for Molten Chloride Salt Systems

Abstract A simply constructed, stable, Ni/Ni2+ saturated reference electrode (SRE) has potential to measure thermodynamic behavior of molten chloride salts more reliably. Like the Ag/Ag+ reference electrode (RE), the Ni/Ni2+ SRE is made of commercially available materials. Initial experiments in molten CaCl2 and LiCl show the Ag/Ag+ RE potential drifting two times faster than the SRE. Furthermore, experiments show the replicability of SREs by comparing two Ni/Ni2+ SREs with different compositions of NiCl2 which is supportive of saturated phase behavior.

Analysis of Kinetic and Ohmic Resistances in PEM Water Electrolysis through Reference Electrode Measurements

Analysis of Kinetic and Ohmic Resistances in PEM Water Electrolysis through Reference Electrode Measurements

Online adaptive anode potential-controlled fast charging of lithium-ion cells using a validated electrochemical model-based virtual reference electrode

Optimal utilization of the safe operating area of lithium-ion battery cells is fundamental to achieving peak performance. Pushing the currents close to the intrinsic electrochemical cell limits during fast charging of battery electric vehicles reduces charging times noticeably and improves customer satisfaction. With electrochemical model-based state observers embedded in the battery management system, predicting the critical anode potential is feasible. This allows the charging process to be adjusted accordingly for effective prevention of lithium plating. However, validating the model, especially the internal potentials, is particularly challenging, and the real-time capability is often doubted. This work addresses the parameterization and experimental validation of a full-order electrochemical model utilizing cells instrumented with micro-reference electrodes. Special emphasis is put on validating the estimate of the anode surface potential, which enables the model to act as a virtual reference electrode. For the first time, it is shown how this can be efficiently implemented on a next-generation automotive microcontroller, in combination with a charging current controller, for online adaptive anode potential-controlled fast charging. Execution times well below 4 ms prove real-time capability, and reference electrodes validate good agreement between model estimate and measurements in closed-loop charging current control.

Graphene Oxide-Poly(vinyl alcohol) Hydrogel-Coated Solid-Contact Ion-Selective Electrodes for Wearable Sweat Potassium Ion Sensing.

Solid-contact ion-selective electrodes (SC-ISEs) with ionophore-based polymer-sensitive membranes have been the major devices in wearable sweat sensors toward electrolyte analysis. However, the toxicity of ionophores in ion-selective membranes (ISMs), for example, valinomycin (K+ ion carrier), is a significant challenge, since the ISM directly contacts the skin during the tests. Herein, we report coating a hydrogel of graphene oxide-poly(vinyl alcohol) (GO-PVA) on the ISM to fabricate hydrogel-based SC-ISEs. The hydrogen bond interaction between GO sheets and PVA chains could enhance the mechanical strength through the formation of a cross-linking network. Comprehensive electrochemical tests have demonstrated that hydrogel-coated K+-SC-ISE maintains Nernstian response sensitivity, high selectivity, and anti-interference ability compared with uncoated K+-SC-ISE. A flexible hydrogel-based K+ sensing device was further fabricated with the integration of a solid-contact reference electrode, which has realized the monitoring of sweat K+ in real time. This work highlights the possibility of hydrogel coating for fabricating biocompatible wearable potentiometric sweat electrolyte sensors.

Effects of carbonation and sponge wetting solution on diffusion potential of carbonated concrete with supplementary cementitious materials

Potential measurement of reinforced concrete is critical for identifying the corrosion state of rebar and monitoring the pH value and chloride concentration of concrete pore solution but remains a challenging task due to the many uncertainties involved. This study aims to investigate the effects of concrete carbonation and the sponge wetting solution on the diffusion potential of partially carbonated concrete blended with supplementary cementitious materials (SCMs). Portland cement is replaced by silica fume (SF), pulverized fly ash (PFA) and ground granulated blast-furnace slag (GGBS) at different replacement levels. Other experimental variables include the degree of concrete carbonation, the wetting solution of the sponge (tap water and 0.3 M NaOH) and the degree of saturation. The results indicate that concrete carbonation-induced diffusion potential would lead to significant errors on the monitoring of the pH value and chloride concentration by measuring the potential between the embedded sensors and external reference electrode. During the pH value and chloride concentration monitoring, 0.3 M NaOH should be used as the wetting solution of sponge for non-carbonated concrete and partially carbonated concrete while tap water should be used for fully carbonated concrete. To some extent, the decline in the degree of concrete saturation can reduce the diffusion potential.

Reliable unencapsulated Ag/Ag2S micro-reference electrodes for battery research and other applications in organic media

Reliable electrochemical measurements depend on the availability of robust reference electrodes (RE) with well-defined potentials. While many reliable REs are known, they are not applicable in certain demanding media such as ionic liquids, nor in small confined spaces. Here, we describe the fabrication of a simple yet robust Ag/Ag2S micro-reference electrode (μ-RE) where a micron-thick Ag2S layer is formed by isothermal reaction with sulfur vapor. Scanning electron microscopy, X-ray photoemission spectroscopy, and spectroscopic ellipsometry characterization reveals that the optimal morphology corresponds to a slightly porous Ag2S film. We demonstrate that the Ag/Ag2S μ-RE can be operated in and cycled through a wide variety of polar organic solvents, including common protic solvents (EtOH), aprotic solvents (ACN, DMSO, NMP, DMF) and ionic liquids (EMIM-TFSI, BMP-TFSI), with short equilibration time (tens of seconds) and little drift (<20 mV), without requiring encapsulation, protective liquid junctions, nor special conditioning. A redox potential of 0.54 ± 0.02 V was obtained for ferrocene in acetonitrile, which places this RE at 0.08 V vs Ag/AgCl. We have also successfully embedded the electrode inside the CR2032 coin cell to perform cyclic voltammetry of battery materials. These results underpin the suitability of this simple micro-reference electrode for a wide variety of electrochemical measurements in demanding and/or miniaturized environments.

A distributed constant equivalent circuit model and a method for estimating parameters for paper-based lactate biofuel cells

In this study, a distributed constant-type equivalent circuit model for paper-based lactate biofuel cells (PBFCs) where the anode and cathode are formed on the same plane was constructed, and a method of determining parameter values in the equivalent circuit model was proposed. When PBFC were prepared and the electrochemical impedance of the entire cell was measured, the Nyquist diagram produced a spectrum due to the current line distribution. Parameters, such as charge transfer and solution resistances, were calculated from the obtained spectrum using theoretical impedance equations derived from the proposed equivalent circuit model proposed. In addition, the behavior of the current distribution in the battery was evaluated in detail by moving the reference electrode on and performing local electrochemical impedance spectroscopy at multiple points on the electrode. The models and methods proposed in this study are good for evaluating systems affected by distributed current lines, such as flat batteries, and for determining cell design, electrode areas, and arrangements.

Photoelectrocatalytic removal of antibiotic ciprofloxacin using a photoanode based on Z-scheme heterojunction

The photoelectrochemical method based on FTO/Fe2O3/BiOI@BiOBr photoanode was applied for the degradation of the ciprofloxacin molecule. The developed method was carried out using a reactor containing ciprofloxacin (3.0 × 10–5 mol L–1), containing a working electrode: FTO/Fe2O3/BiOI@BiOBr, a platinized titanium counter electrode and an Ag/AgCl/KCl (3.0 mol L–1) reference electrode, working potential of 2.0 V with ultraviolet radiation (9.0 W). The electrode was characterized by electrochemical, morphological, structural and optical techniques. When applying the degradation method, after one hour, the antibiotic molecule was degraded more than 90.0 %, being mineralized close to 52.0 %, in which the degraded samples were characterized by UV–vis spectrometry, determination of total organic carbon and UHPLC-Q-ToF-MS. Like this, the oxidation process proved to be efficient yielded a kinetic constant k = 3.7 × 10–2 min−1 and a half-life of 18.7 min. The charge transfer mechanism in the photoanode semiconductor material occurred by a Z-scheme recombination process. Finally, the mass spectroscopy experiments demonstrated that the ciprofloxacin oxidation process led to the formation of fourteen by-products, in which the degradation path was proposed in three steps.

Multi‐Parametric Decision System for Analytical Performance Assessment of Electrochemical (Bio)Sensors

AbstractMiniaturized three‐electrode electrochemical sensors (MES) are widely used in the advancement of innovative technologies for remote sensing applications. MESs consist of conductive electrodes that are applied onto an inert solid substrate using various techniques, such as photolithography, electroplating, and screen printing. Typical MES systems comprise working (WE) and counter (CE) electrodes based on gold (Au), paired with a reference electrode (RE) based on silver (Ag). This configuration is commonly selected due to Au's high conductivity, low resistance, and compatibility with robust organothiol chemistries, especially for the WE. Moreover, Ag is often preferred for REs owing to its low toxicity, stability, and high conductivity. Nevertheless, in uncontrolled environments outside of cleanrooms, both Au and Ag surfaces are prone to atmospheric contamination, resulting in significant sensor variability and compromised analytical performance. Therefore, it is crucial to integrate a pre‐processing stage into the sensor manufacturing process to guarantee the quality and cleanliness of MES electrode surfaces for sensor functionalization and precise electrochemical measurements. Considering the potential negative effects of methods tailored for a specific electrode material on another material, this study extensively investigates 18 different treatment methods for MESs incorporating Au CEs and WEs, along with Ag REs. Employing a multi‐parametric analysis, this study aims to identify the most effective treatment for a variety of electrode materials, thereby improving analytical accuracy and reproducibility for subsequent MES (bio)sensor applications.

Development of Ag2O–TeO2-based glass and glass/stainless steel reference electrodes for pH sensors

Glass pH sensors are unsuitable for in vivo biomedical, clinical, or food applications because of the brittleness of glass, the difficulty in measuring small volumes and complicated matrix, and the necessity of calibration. Enamel structures such as glass/stainless steel (SUS) may substitute glass-based pH electrodes. This study developed new reference electrodes for pH sensors using ternary Ag2O–TeO2-MaOb (M = B, Ge, and P) glass and glass/SUS. The effect of the partial replacement of TeO2 in Ag2O–TeO2 glasses with B2O3, GeO2, and P2O5 on the pH sensitivity was investigated. (1) The effect of the partial replacement on the pH 4–9 sensitivity, which is defined as 100% for the ideal working electrode and 0% for the ideal reference electrode estimated from pH potential, became prominent in the order of GeO2, B2O3, and P2O5 in glass electrodes. Ag2O–TeO2–B2O3 glasses showed the lowest pH 7–9 sensitivity of 1% among the present electrodes. Ag2O–TeO2–P2O5 glasses showed the lowest pH 4–9 sensitivities of 24–33% among the present electrodes. (2) 25Ag2O･55TeO2･20P2O5/SUS showed a very low pH 4–9 sensitivity of 5% in glass/SUS electrodes. In this case, AgP2 may be responsible for the low pH 4–9 sensitivity because only AgP2 was detected from XRD measurements, and a small particle on the surface was observed in AFM observations. On the other hand, the crystallization of the glass matrix of 25Ag2O･55TeO2･20P2O5/SUS was suppressed by adding P2O5. Thus, 25Ag2O･55TeO2･20P2O5/SUS is a candidate for a robust KCl-leakless reference electrode for pH sensors.

Reference Electrodes in Proton Exchange Membrane Water Electrolysis: Previous Approaches, Current Application, and Perspectives

Abstract The commercialization of proton exchange membrane water electrolysis cells (PEMWEs), which are essential for a greener and more sustainable future, is hindered by the high costs of noble metal catalysts, as well as the degradation of the catalysts and membranes. Examining the electrodes' characteristics with reference electrodes (REs) yields insights into their individual performance and can, e.g., help assess new catalyst layer designs, their interplay with the adjacent porous transport layer, or understand the complex and multi-faceted degradation mechanisms. This review provides an overview of previous approaches and the evolution of RE designs in PEMWE. By discussing the strengths and limitations of different RE setups, readers are enabled to make more informed decisions about their experiments' design and choose the best RE setup for their specific research question.

Long-Term Performance of Ag/AgCl Reference Electrodes for Corrosion Potential Monitoring in Radioactive Tank Waste at the Hanford Site

ABSTRACT This work studied the exposure effects from radioactive tank waste on long-term performance of single junction Ag/AgCl reference electrodes for corrosion potential monitoring at the Hanford Site. Electrodes from three manufacturers with very different designs were studied using open-circuit potential and electrochemical impedance measurements in radioactive tank waste. Post-test analyses were conducted on some failed electrodes using destructive and non-destructive techniques. Intrusion of the aggressive and radioactive chemicals in tank waste through the porous frit materials was the primary mechanism that led to clogging of frit, physical and chemical degradation of AgCl bonded to Ag wire, and alteration of the internal electrolyte. Radiolytic chemical species such as H2O2 and HNO3 may have also induced degradation of the Ag wire. The extent of electrode degradation and failure probability highly depended on the electrode design and environment conditions. Chemicals in tank waste had stronger effects than radiation on the long-term performance of the Ag/AgCl reference electrodes.

SrMoO4-based mixed-potential gas sensor for NH3 sensing in direct ammonia-fed fuel cells

Direct ammonia-fed fuel cells (DAFCs) are well known for sustainable energy production. However, the issue is a certain amount of unreacted NH3 fuel is obtained at the outlet. Thus, real-time monitoring and quantification are of utmost importance, nevertheless, this is troublesome due to the harsh thermodynamic conditions. This work aims to develop a mixed-potential sensing electrode for the detection of NH3 under reducing conditions (H2 atmosphere) at high temperatures. In this regard, a strontium molybdate (SrMoO4) sensing electrode (SE) is a potential solution due to its physical and chemical stability, along with its sensitivity to NH3 under reducing conditions. Therefore, an SrMoO4-based mixed-potential sensor is fabricated herein using yttria-stabilized zirconia (YSZ) as the electrolyte and platinum (Pt) as the reference electrode (RE) and is operated at 400–650 ℃. The maximum response exhibits about –21.57 mV toward 80 ppm NH3 at 500 ℃. Further, the sensitivity is –17.19 mV/decade towards 10–60 ppm and –45.33 mV/decade towards 60–320 ppm NH3 under 75% H2 balanced by N2 at 500 ℃. The as-fabricated sensor also has good selectivity towards NH3 and good cross-sensitivity towards other interfering gases and is stable in long-term repeated operation. The direct current (DC) polarization curves and electrochemical impedance spectroscopy (EIS) results demonstrate the sensing mechanism in accordance with the mixed-potential theory.

Printing technologies for the fabrication of ion-selective electrodes

The fabrication of ion-selective electrodes (ISEs) via printing technologies such as screen-printing, inkjet printing, and 3D printing is attracting increasing attention due to the superb reproducibility and scalability of these technologies. In contrast to traditional manual casting, coating, and assembling procedures often used in research labs, printing methods are much more compatible with manufacturing processes in industry and, therefore, are easier to scale up. In this paper, we first summarized and compared the printing mechanisms and ink requirements of screen printing, inkjet printing, and 3D printing technologies. Then we present an overview of how different printing technologies can create sensor components, such as electrical contact layers, ion-to-electron transduction layers, ion sensing membranes, reference electrode membranes, insulation layers, and microfluidic/detection housings. The printing protocol, ink material, and sensor performance are highlighted for a few selected ISEs. This review concludes with a summary of the advantages and drawbacks of various printing technologies.

Shedding Light on the Failure Factors of Subsea Critical Fastener Bolts

Offshore facilities, such as oil and gas rigs, wind turbines, and related subsea equipment, typically use flanges fastened using bolts and nuts as the main connectors. In this study, multidisciplinary parameters, namely the preload torque used to tighten bolts, simulated subsea water currents, water temperature, and impressed current cathodic protection, were applied to ASTM A193 B7 bolts. An experimental supervisory control and data acquisition system was designed to obtain measurements every 5 min throughout a 21-day experiment. Finite element analysis was performed to predict the structurally vulnerable areas of the bolts. A strong correlation was found between the reference electrode readings and the measured electrical current, tightening torque, and water temperature. As the water temperature rises during the day, the reference electrode reading becomes less negative and the electrical current decreases. Subsea water currents cause about a four-time increase in the bolt corrosion rate, with unprotected bolts suffering a nine-time-higher corrosion rate than protected bolts. A unique supply–demand interaction is observed; less protection is supplied to areas with lower corrosion rates (lower demand for protection). Finally, scanning electron microscopy examination reveals new insights into the failure mechanisms of subsea bolts.

Miniaturized inkjet-printed flexible ion-selective sensing electrodes with the addition of graphene in PVC layer for fast response real-time monitoring applications

In this letter, we propose a miniaturization scheme of inkjet printed ionic sensing electrodes by adding graphene into the ion-selective PVC film not only to reduce the impedance of the ionic liquid layer of the electrode but also to increase the electrode capacitance for the reduction of the response time. Based on the scheme, we present a fully inkjet-printed electrochemical ion-selective sensor comprising a working electrode and reference electrode, which are inkjet-printed Ag NPs/PEDOT:PSS-graphene/PVC-graphene and Ag/AgCl(s)/ionic liquid PVC-graphene layer structures, respectively. The printed ion-selective working electrode has been miniaturized to a size of 22,400 μm2 equivalent to a square shape of ∼150 × 150 μm2 comparable to the size of a human cell. By adding graphene to the ion selective PVC film, more than 90 % charge transfer resistance reduction can be achieved and the shunt capacitance is increased by 3.4-fold in shunt capacitance compared to the film without graphene, thereby more than 33 % reduction of the response time required to reach equilibrium. Meanwhile, these miniaturized potassium sensors using the working electrodes with/without adding graphene have been integrated with in-lab signal-processing and wireless-transmission module to yield similar results to the one measured by commercial electrochemical workstation showing a great potential for real-time monitoring in portable clinical trials. Specifically, the proposed sensor utilizing graphene-enhanced electrodes demonstrates a linearity uncertainty of 2.9 mV, which is approximately half of the uncertainty observed in the sensors lacking graphene integration.

Nonaggregated Anions Enable the Undercooled Aqueous Electrolyte for Low-Temperature Applications.

Aqueous batteries, with the advantages of high safety and low cost, are highly promising for large-scale energy storage. However, freezing of the aqueous electrolyte limits the low-temperature operation. Here, we propose and achieve a highly dispersed solvation structure in the electrolyte by coupling nonaggregated Cl- anions, which reduces the water cluster size and prevents the solidification of the aqueous electrolyte until -136.3 °C. The low-temperature LiCl electrolyte exhibits a high ionic conductivity (1.0 mS cm-1) at -80 °C and enables a stable low-temperature Ag/AgCl reference electrode at -50 °C. Moreover, the polyaniline-based battery can work at an extremely low temperature of -100 °C and shows superior cycling performance of 4000 cycles at -40 °C with 95.7% capacity retention. This work elucidates the correlation between the anion effect and the thermodynamic transition of the electrolyte, offering a novel approach for designing low-temperature electrolytes.