Electrolyte Bridge Research Articles

Reference-Electrode Configuration in CO2 Electrolysis (CO2E) and Anion-Exchange Membrane Water Electrolysis (AEMWE) Cells for Degradation and Stability Evaluation

CO2 electrolysis (CO2E) and anion-exchange membrane water electrolysis (AEMWE) have both been identified as promising technologies for reducing emissions from the industrial and energy sectors in pursuit of achieving net-zero goals.1,2,3,4 Recent developments of electrocatalysts, membranes, and electrolyser cell design have resulted in rapid progress of CO2E and AEMWE, achieving high current densities and faradaic efficiencies at the laboratory scale.1,2 However, the long-term stability of these technologies requires improvement if they are to be deployed at commercially relevant scales.2,5 Unfortunately, degradation phenomena such as; cathode flooding6, 10, catalyst degradation7, membrane instability8,9, and salt precipitation10 are difficult to diagnose electrochemically, without the ability to decouple resistance contributions in-situ.We have therefore developed a 3-electrode technique and explored protocols that allow for the decoupling of cathode and anode overpotentials during long-term stability measurements.By using an edge-type reference electrode connected to the membrane through a liquid electrolyte bridge, we successfully demonstrate the ability to assess the performance of individual components within different membrane-electrode assembly (MEA) configurations. We highlight instabilities with using edge-type reference electrodes such as changes in the pH of the electrolyte bridge, and discuss efforts to mitigate these issues to permit long-term stability testing. We then demonstrate how this method can be used to provide more insights into degradation phenomena in both CO2 and AEM water electrolyser cells, showing early diagnosis - up to 7 hours before detection from a conventional 2-electrode set-up - of failure mechanisms during stability testing.The proposed 3-electrode technique is capable of separating anode and cathode overpotentials over the course of extended testing periods and provides a platform to study the electrochemical response of individual electrolyser components to various degradation phenomena, and the durability of CO2E and AEMWE materials. Critical gaps in knowledge surrounding these issues can be better understood, which will enable these technologies to advance to the next stages of development.

Investigation of Hydrogen Starvation of Polymer Electrolyte Fuel Cells in Freezing Condition Using Reference Electrode

For vehicles using polymer electrolyte fuel cells (PEFCs) to be commercially competitive with conventional internal combustion engine vehicles, three major challenges must be resolved, i.e., cost, performance and durability (1). The durability of a PEFC system can be largely affected by hydrogen starvation. During the startup/shut down process (2) of the fuel cell system, or when the flow channel is blocked by water or ice, local hydrogen starvation arises within one or many of the cells in the fuel cell stack. When this happens, hydrogen oxidation reaction (HOR) on the anode side cannot support the current imposed by the other cells. In that case, the anode half-cell potential increases relative to the cathode potential, and the cell voltage reverses. The high anode half-cell potential during cell reversal leads to water electrolysis and carbon corrosion reaction, the latter of which causes damage to the carbon support in the catalyst layer and leads to severe cell performance degradation. Hydrogen starvation in normal operating condition has been extensively investigated (3-5). However, little research has been conducted on cell reversal at sub-zero temperatures. In past work on studying cell reversal, the anode potential and the corresponding reactions are estimated from the fuel cell voltage assuming a stable cathode potential. However, at sub-zero temperatures, ice formation affects both the anode and cathode potentials, which makes it difficult to evaluate the cell reversal origin and the anode half-cell potential. To better understand hydrogen starvation and cell reversal behavior of PEFCs sub-zero temperatures, a specially designed, easy-handling reference electrode has been developed and integrated with the membrane electrode assembly (MEA) in order to separate anode and cathode potentials, as shown in Fig. 1. The external hydrogen reference electrode is attached to the MEA through a thin polymer electrolyte bridge. With the reference electrode installed, the cell reversal behavior is investigated for both the typical operating temperatures (65-80 oC) and the sub-zero temperatures (e.g., -15 oC). At 65 oC, the cell voltage change during hydrogen starvation is mainly affected by anode potential change, which shows the potential plateau for water electrolysis and carbon corrosion. In contrast, the cell voltage experiences several transient states at -15 oC. Using the reference electrode, we identify that only one of the potential plateaus in caused by changes in the anode potential and the remainder are a result of phenomena related to ice formation in the cathode. Herein, we present several unique aspects related to hydrogen starvation cell reversal at sub-zero temperatures that are identified using the reference electrode. Figure 1

The Utilization of Hydrophobic Coatings on Insulative Skirts to Galvanically Decouple Mechanically-Fastened Aluminum Alloy and Carbon-Fiber Reinforced Polymer-Matrix Composites

In a quest to reduce weight and improve performance, aluminum (Al) alloys have been used in conjunction with lightweight materials such as carbon-fiber reinforced (CFR) polymer-matrix composites (PMCs). The mechanical contact of CFR PMCs (which serves as cathode) with Al alloys (which serves as anode) can result in galvanic corrosion of the Al alloys in a corrosive environment. The major objective of this research was on devising corrosion control strategies for couples of 6061-T6 Al that were mechanically fastened to CFR PMCs using Ti-6Al-4V bolts. A typical method used to mitigate galvanic corrosion when bolting Al to CFR PMCs is to insert an insulating layer (G-10 fiberglass or E-glass–reinforced PMC) between the members. Although the direct contact between the aluminum and CFR PMC is eliminated, the aluminum and the CFR PMC are still galvanically coupled through the Ti fastener, and galvanic corrosion on Al will occur if the electrolyte bridges over the insulating layer. Galvanic corrosion can be mitigated by increasing the IR loss across the skirt, which can be achieved by lengthening the skirt or breaking up the continuity of the salt bridge that forms on the skirt. The continuity of the salt bridge can be disrupted by applying hydrophobic coatings on the insulative skirt. In this study, galvanic corrosion rates were monitored for 6061-T6 Al—CFR PMC couples (with insulating skirts) subjected to the following conditions: 1) Insulting skirts having coatings (silane-based coating, epoxy, polyurethane, or latex) of various levels of hydrophobicity 2) Salt solutions of various concentrations (0, 10, 100, 1000, 10000, and 20000 ppm of chlorides) 3) Various insulating skirt lengths (0.25 inch or 0.5 inch), 4) Various exposure conditions (controlled humidity laboratory exposure, outdoor exposure with sheltered and unsheltered conditions). The effect on galvanic corrosion by the different coatings was studied as a function of hydrophobicity, as determined by the contact angle for wetting. The contact angle was measured on the coating surface before and after exposure to the outdoor test sites to study the effects of environmental degradation on hydrophobicity. The degradation of the coatings was also studied using other techniques such as Raman spectroscopy. The ingress of environmental constituents (i.e., chlorides, sodium ions, etc.,) towards the anode and cathode surfaces was analyzed using scanning electron microscopy (SEM) and energy dispersive-X-ray analysis (EDXA).

CONCEPTUAL MODEL OF COMMUTATION MECHANISM FOR ELECTRIC CONDUCTIVITY OF VAPOR-GAS ENVELOPE IN ELECTRO-IMPULSE POLISHING MODE

Electric conductivity of vapor-gas envelope in electro-impulse polishing mode is closely connected with mechanisms of physical and chemical processes occurring on an anode surface and in pre-anode area of electrolyte, metal removing, smoothing-out of surface profile irregularities and technological regimes influencing on productivity and processing accuracy. The paper presents experimentally substantiated conceptual model of a mechanism for electric conductivity of vapor-gas envelope. According to the model an electric current passing in the envelope and having quasi-constant and high-frequency components is provided by ionic conductivity in electrolyte envelope-enclosing bridges and ionic conductivity in gas envelope phase. It has been shown that quasi-constant of the current component represents a composition of electric current consisting of overlapping time current impulses from electrolyte bridges that enclose the envelope with frequency of 0.01−0.90 kHz and current in a gas phase of the envelope. High-frequency current component is pre-conditioned by ionic conductivity in bridges that commutate the envelope with frequency of 2.5 MHz. The paper theoretically substantiates excessive electrical conductivity of electrolyte in the electrolyte bridges. It has been demonstrated that formation of vapor-gas envelope and its renovation are connected with thermal burst mechanism for destruction of electrolyte bridges. Envelope vibration and hydrodynamic flows within the electrolyte occur due to impulse wave impact on electrolyte layer which is on the border of the envelope. The waves are caused by burtsts of electrolyte bridges and cavitation bubble collapse in pre-anode electrolyte area.

The Attenuation of Galvanic Corrosion Between Mechanically-Coupled Aluminum and Polymer Matrix Composites (PMCs) Using Hydrophobic, Insulative Skirt Materials

OBJECTIVE The objective of this research is to study the effect of hydrophobic, insulative skirt materials on the galvanic corrosion of mechanically-coupled aluminum and polymer matrix composites (PMCs)to develop effective corrosion mitigation solutions. INTRODUCTION Metal-PMC structures are being used more and more in military and civilian applications. PMCs, for example, are being used with greater frequency in defense, aerospace, automotive and civil-infrastructure industries. In the quest to reduce weight and increase performance, more and more advanced structures, systems and machines are being developed using a combination of alloys, composites, polymers, and ceramics. A system of dissimilar materials, however, may induce significant corrosion problems. Metal alloys coupled to composites may lead to crevice and galvanic corrosion problems. Corrosion control strategies need to be incorporated into the design of mechanically coupled metal-PMC joints to improve corrosion resistance and decrease maintenance and repair time. BACKGROUND Electrically conductive PMCs such as carbon fiber reinforced (CFR) PMC can accelerate the corrosion at PMC-Al interfaces by galvanic action and crevice corrosion. A typical method used to mitigate galvanic corrosion when bolting aluminum to CFR PMCs is to insert an insulating skirt between the members (Figure 1) to eliminate direct contact. However, aluminum and CFR PMCs are still galvanically coupled through the fastener; hence, galvanic corrosion can occur if the electrolyte bridges over the insulating skirt. To attenuate the galvanic effect, the insulating skirt can be extended beyond the CFR PMC coupon to various lengths (Figure 1). APPROACH The galvanic corrosion rate is a function of Ohmic loss (IR loss) between Al (anode) and PMC (cathode), and the polarization behavior of the anode and cathode. The Ohmic loss depends on the ionic conductivity of the electrolyte film that forms on the insulating skirt. The parameters that affect the ionic conductivity of the electrolyte film are salt loading (m’) (e.g., various Cl- concentrations), length of the insulating skirt (ls ), and humidity. A relationship between galvanic corrosion rate and skirt length-to-salt loading ratio (ls /m’) was established.Another parameter that affects the effective skirt length to attenuate galvanic corrosion is the continuity of the electrolyte layer on the skirt. Hence, hydrophobicity of the skirt material is an important parameter in determining the effective skirt length. The insulating skirts of various lengths were coated with different coatings (Figure 2) and the hydrophobicity was determined using contact angle measurements.The galvanic corrosion rate of 6061-T6 Al alloy coupled to CFR PMC were monitored over a 3-day period inside of a humidity chamber at 90% relative humidity (RH) and 30oC using the zero resistance ammeter (ZRA) technique with different skirt lengths which were coated and uncoated. The samples were sprayed with various concentrations of salt solutions. The galvanic corrosion rates were monitored for different types of coatings on the insulating skirt (hydrophobicity), electrolyte type, humidity, and various skirt lengths. Measurements were also be taken in the field. ACKNOWLEDGEMENTS The authors are grateful for the support from the Office of the Under Secretary of Defense for the project entitled “Corrosion and Corrosion Control Studies of Aluminum Alloys that are Mechanically-Coupled or Adhesively-Bonded to Polymer-Matrix Composites in Diverse Micro-Climates” (U.S. Air Force Academy, USAFA–BAA-2009-1). The authors are particularly grateful to Mr. Daniel Dunmire, Director, Corrosion Policy and Oversight, Office of the Under Secretary of Defense. The authors are also grateful to other members of the Department of Defense Technical Corrosion Collaboration: Mr. Richard Kinzie, Mr. Larry Lee, Dr. William Abbott, Dr. David Robertson, Mr. Richard Hays, and Dr. Christopher Scurlock.

Classification of Bridge Current and Analysis of Heat Transfer Characteristics in Polyvinyl-Chloride-Sheathed Flat Cord Under Tracking

In this study, we examine the tracking happen in a polyvinyl-chloride-sheathed flat cord (PVCSFC), which is widely used as a distribution cord. The study classifies the bridge current via the formed conductive paths during tracking in the PVCSFC. Further, it attempts to distinguish the characteristics of heat generation and heat transfer by kind of bridge current. When the PVCSFC is in the static state, the bridge currents flow only through the electrolyte bridge. In the case of the carbonized PVCSFC, the bridge currents flow through one or more conductive paths. One is the electrolyte bridge, the other is the bridge that is consisted electrolyte and carbonized insulation. Currents flowing through different conductive paths have different heat generation and transfer characteristics. As the bridge current flowing in the conductive path consisting of electrolyte and carbonized insulation increases, the temperature difference between the surface of the PVCSFC and ambient air also increases correspondingly.

Contact Electrochemical Replication of Hydrophilic−Hydrophobic Monolayer Patterns

Contact electrochemical replication (CER) is a novel pattern replication methodology advanced in this laboratory that offers the unprecedented capability of direct one-step reproduction of monolayer surface patterns consisting of hydrophilic domains surrounded by a hydrophobic monolayer background (hydrophilic @ hydrophobic monolayer patterns), regardless of how the initial "master" pattern was created. CER is based on the direct electrochemical transfer of information, through aqueous electrolyte bridges acting as an information transfer medium, between two organosilane monolayers self-assembled on smooth silicon wafer surfaces. Upon the application of an appropriate voltage bias between a patterned monolayer/silicon specimen playing the role of "stamp" and a monolayer/silicon specimen playing the role of "target", the hydrophilic features of the stamp are copied onto the hydrophobic surface of the target. It is shown that this electrochemical printing process may be implemented under a variety of experimental configurations conducive to the formation of nanometric electrolyte bridges between stamp and target; however, using plain liquid water for this purpose is, in general, not satisfactory because of the high surface tension, volatility, and incompressibility of water. High-fidelity replication of monolayer patterns with variable size of hydrophilic features was achieved by replacing water with a sponge-like hydrogel that is nonvolatile, compressible, and binds specifically to the hydrophilic features of such patterns. Since any copy resulting from the CER process can equally perform as stamp in a subsequent CER step, this methodology offers the rather unique option of multiple parallel reproduction of an initially fabricated master pattern.

Electrical properties of a graphite-rich quartzite from a former lower continental crust exposed in the Serre San Bruno, Calabria (southern Italy)

In this study electrical properties of a graphite-rich quartzite from the former lower crust exposed in the Serre San Bruno, Calabria (southern Italy) have been analysed by means of complex electrical conductivity measurements in the frequency range 10 −3 to 10 6 Hz on plug samples of 25 mm in diameter and 22 mm high. The samples were identified as a former oil sandstones containing up to 12–15% flake-like graphite, which present highly metamorphosed relics of its former hydrocarbon filling. Though high concentrations of graphite were detected, the graphite quartzite is highly resistive. The spatial ordering of isolated graphite grains like tiles prevent the generation of interconnected electrical pathways. These isolated good conductors are interconnected by electrolyte bridges, thus causing the high polarizability, indicating redox reactions at the electrolyte/graphite interfaces that could be modelled using CPE elements. The type of graphite ordering was caused by the early formation of isolated oil droplets in the reservoir sandstone. After high-grade metamorphism and shearing, they appear as flat graphite grains in the foliation plane and were smeared together because of the rigidity of sillimanite and quartz, the main rock constituents. Thus this graphite quartzite is by no means a candidate to enhance the electrical conductivity of the deep continental crust. Syngenetic graphite in former lower crustal rocks is largely resistant against varying geochemical conditions during prograde and retrograde metamorphism. This had also been shown for graphite that is contained in normal metapelites as accessory mineral, or enriched in former black shales where it may cause high conductivity [Jödicke, H., Kruhl, J.H., Ballhaus, C., Giese, P., Untiedt, J., 2004. Syngenetic, thin graphite-rich horizons in lower crustal rocks from the Serre San Bruno, Calabria (Italy), and implications for the nature of high-conducting deep crustal layers. PEPI 141, 37–58; Nover, G., 2005. Electrical properties of crustal and mantle rocks—a review of laboratory measurements and their explanations. Surv. Geophys. 26 (5), 593–651].

Dual Electrodes Oxidation of Dye Wastewater with Gas Diffusion Cathode

The high energy cost of an electrochemical method is the fatal drawback that hinders its large scale application in wastewater treatment. In traditional single-chamber electrolysis cell, only direct oxidation at an anode exists. Although a small amount of hydrogen peroxide is produced at the cathode by reduction, it is transferred to the anode and destroyed there without adding much benefit to organic decomposition. A two-chamber electrolytic cell, connected with an electrolyte bridge, was developed in this work. In this new reactor, direct oxidation at anode and indirect oxidation by hydrogen peroxide at cathode can occur simultaneously. Therefore "dual electrodes oxidation" in one electrochemical reactor was achieved successfully. Compared to a traditional one cell reactor, this reactor cuts the energy cost by 50%, and thus might lead to reconsideration of the electrochemical role in wastewater treatment. A Pt/C gas diffusion electrode (GDE) is fabricated and used as a cathode fed with oxygen-containing gases to produce hydrogen peroxide. When purified air diffuses through the active layer on the GDE, oxygen is reduced to hydrogen peroxide with a high yield to decompose organics. It has been found that the direct oxidation process at an anodic zone is slightly affected by factors such as pH variation, Fe(II) existence and aeration, while indirect oxidation at the cathodic zone is strongly affected. Dye used as a model pollutant was oxidized into small organic acids in both anode and cathode regions in this electrolytic reactor. GC-MS and IR spectrum were employed to analyze the intermediates formed during the degradation. Twenty intermediates have been detected, including 14 esters, 3 acids and 3 compounds with NO2 or N-OH groups. Thereafter, the degradation pathways of dye Acid Red B are proposed.

A convenient method for detecting electrolyte bridges in multichannel electroencephalogram and event-related potential recordings

Dense electrode arrays offer numerous advantages over single channel electroencephalogram/event-related potential (EEG/ERP) recordings, but also exaggerate the influence of common error sources arising from the preparation of scalp placements. Even with conventional low density recordings (e.g. 30-channel Electro-Cap), over-application of electrode gel may result in electrolyte leakage and create low impedance bridges, particularly at vertically-aligned sites (e.g. inferior-lateral). The ensuing electrical short produces an artificial similarity of ERPs at neighboring sites that distorts the ERP topography. This artifact is not immediately apparent in group averages, and may even go undetected after visual inspection of the individual ERP waveforms. Besides adding noise variance to the topography, this error source also has the capacity to introduce systematic, localized artifacts (e.g. add or remove evidence of lateralized activity). Electrolyte bridges causing these artifacts can be easily detected by a simple variant of the Hjorth algorithm (intrinsic Hjorth), in which spatial interelectrode distances are replaced by an electrical analog of distance (i.e. the variances of the difference waveforms for all pairwise combinations of electrodes). When a low impedance bridge exists, the Hjorth algorithm identifies all affected sites as flat lines that are readily distinguishable from Hjorth waveforms at unbridged electrodes.

Estimation of the thermal liquid junction potential of an external pressure balanced reference electrode

The accurate measurement of pH and potential in high-temperature high-pressure aqueous solutions using an external pressure balanced reference electrode (EPBRE) requires the development of accurate methods for calculating the thermal liquid junction potential (TLJP). Using well-developed irreversible thermodynamic techniques, as well as Agar's hydrodynamic theory to calculate the ionic entropies of transport, we show that the TLJP makes a very significant contribution to the measured potential and can vary by more than ± 150 mV depending on the temperature and composition of the non-isothermal electrolyte bridge. Our calculations of the TLJP are compared with experimentally measured data and good agreement is obtained. The development of an advanced EPBRE, in which the composition of the non-isothermal liquid junction is maintained accurately at a well-defined concentration, is considered to be an appropriate way to solve the problem of performing accurate potentiometric measurements in high-temperature high-pressure aqueous systems.

Theory of multiple-cell response of redox electrodes

The theory is developed of the voltage of several cells connected in series that have an electrolyte bridge between each cell. The measured voltage increases as the ratio of the electrolyte resistance between cells to that within each cell is increased. Experiments with half cell compartments with platinum and silver electrodes in 0.001 mol dm−3 potassium permanganate solution connected by thin tubes of different lengths showed a fit to theory if a small constant resistance was included.

Reference electrode sites for potential difference measurements in the gastrointestinal tract.

Simpler alternatives to the use of an intravenous reference electrode for potential difference measurement in the gastrointestinal tract were considered. Lancet puncture of the forearm skin, and intradermal injection of 0.1 ml 154 mmol/l NaCl into the forearm were shown to effectively abolish the skin-blood potential difference, thereby rendering such sites suitable for reference electrode placement. Another acceptable method was to use an intravenous "butterfly" cannula filled with heparinized saline. The tip of the electrolyte bridge was inserted into the distal end of the cannula, thereby making indirect contact with the bloodstream. It is suggested that the use of any one of these three methods of reference electrode placement would facilitate the measurement of esophageal or gastrointestinal potential difference during a routine endoscopy without significantly altering the accuracy of the measurements.

Measurement of gastrointestinal transmural electric potential difference in man.

Measurement, in man, of the electric potential difference between venous blood and the mucosal surface of the gastrointestinal tract gave identical values to the potential difference between mucosa and serosa. Various parts of the peritoneum were equipotential with venous blood. By contrast, skin-enteric potential difference varied with time and among different subjects because of a potential difference between skin and blood that is unpredictably reduced by skin injury. The results with electrolyte bridges of KCl in agar or of flowing KCl were identical.

Gastroesophageal transmural potential difference measured by a new constant infusion method. The effect of skin scarification on this potential difference.

An improved method of measurement of potential difference (PD) in the stomach and esophagus was devised. The exploring electrolyte bridge was a polyvinyl tube through which Ringer's solution was infused at a constant speed of 0.382 ml./min. With this method, a steadier PD reading could be obtained than with the methods previously described. The exclusion of concentrated potassium chloride from the system made the exploring probe less traumatic to the gastrointestinal mucosa. Simultaneous PD and intraluminal pressure recordings using the constant infusion technic could be achieved with ease. The artifact and variation due to presence and the changes of skin potential were excluded by means of superficial scarification of the skin.

An Assembly for Electrochemical Corrosion Studies in Aqueous Environments at High Temperature and Pressure

Abstract An assembly is described, in which electrochemical corrosion measurements can be carried out in aqueous environments up to 314 C (598 F) and 105.5 kg/cm2. Test specimen mounting and corrosive environment containment procedures are discussed. A techniqie for using a high pressure electrolyte bridge with an external reference electrode is described. The performance of the system is demonstrated by potentiostatic anodic, cathodic and linear polarization experiments carried out on AISI Type 304 steel in dilute chloride solutions at 289 C.