Academic literature on the topic 'POTENTIAL CATHODE'

Abstract Electrochemical (EC) treatment presents a low-energy, water-reuse strategy with potential application to decentralized greywater treatment. This study focused on evaluating the impacts of cell configuration, current density, and cathode material on chemical oxygen demand (COD) removal and disinfection byproduct (DBP) formation in greywater. The formation and/or cathodic removal of active chlorine, perchlorate, haloacetic acids, and trihalomethanes were assessed during EC treatment. DBP formation was proportional to current density in undivided EC cells. Sequential anodic-cathodic treatment in divided EC cells resulted in COD removal in the catholyte and anolyte. The anodic COD removal rate (using a mixed metal-oxide anode) was greater than the cathodic removal rate employing boron-doped diamond (BDD) or graphite cathodes, but anodic and cathodic COD removal was similar when a stainless-steel cathode was used. The overall energy demand required for 50% COD removal was 24% less in the divided cells using the graphite or BDD cathodes (13 W-h L−1) compared to undivided cells (20 W-h L−1). Perchlorate formation was observed in undivided experiments (>50 μg/L), but not detected in divided experiments. While haloacetic acids (HAAs) and trihalomethanes (THMs) were generated anodically; they were removed on the cathode surface in the divided cell. These results suggest that divided configurations provide potential to mitigate DBPs in water reuse applications.

Electrochemical reduction of hydrogen (hydronium ion) was carried out on zinc, aluminum and copper cathodes from acidic aqueous solutions containing sulfuric acid (0.09, 0.18 and 0.36 mol/l) to study the effect of electrolyte acidity, the type of cathodes used and potential values on electrolysis indicators. The studies were carried out on the potentiostat using a three-electrode cell under conditions of intensive electrolyte stirring with a magnetic stirrer. At the initial stage, electrolysis was performed in the following modes: potentiodynamic measurements at a sweep rate of 1 mV/s in the potential range Е = –(700÷850) mV on a copper and aluminum electrode and Е = –(1000÷1150) mV on a zinc electrode. In the indicated potential range, hydronium discharge parameters at each cathode were calculated: Tafel slope, apparent transfer coefficients and exchange currents. Dependences of these parameters on electrolyte acidity were considered. Average values of steady state potentials were obtained, which, similar to the apparent exchange current, significantly depended on the cathode material: –923.1 mV (zinc cathode); +36.1 mV (copper cathode), and –603.7 mV (aluminum cathode) (AgCl/Ag). The effect of surfactants on all the kinetic parameters considered was shown. The order of the reaction with and without surfactant additives was determined. At the next stage, the electrochemical parameters of hydronium discharge on the copper electrode only were compared. It was shown that the electrochemical parameters significantly depend on the cathodic potential range where they are determined, and on the methods used for their calculation. It was noted that the process proceeds in the region of mixed kinetics. As the electrode polarization decreases, the hydrogen discharge mechanism changes, while the proportion of electrochemical kinetics will increase in the region of mixed kinetics. We suppose that the data obtained can also be of practical importance for the zinc electrolysis technology. The data obtained in this research on the electrochemical parameters of hydrogen discharge in a wide range of potentials on cathodes made of different metals as well as on the effect of electrolyte acidity on the behavior of surfactants during electrolysis will expand knowledge about the zinc electrolysis technology.

Lithium-ion battery (Li-ion) is an energy storage device widely used in various types of electronic devices. The cathode is one of its main components, which was developed because it accelerates the transfer of electrons and battery cycle stability. Therefore, the LiNixMnyCozO2 (LNMC) cathode material, which has a discharge capacity of less than 200 mAh g−1, was further developed. Li-Mn-rich oxide cathode material (LMR-NMC) has also received considerable attention because it produces batteries with a specific capacity of more than 250 mAh g−1 at high voltages. The structure, synthesis method, and sintering temperature in the fabrication of LMR-NMC cathode materials affect battery performance. Furthermore, manganese sulphate fertilizer replaces manganese sulphate as raw material for LMR-NMC cathode due to its lower price. The method used in this study was implemented by reviewing previous literature related to Li-ion batteries, Li-ion battery cathodes, synthesis of LMR-NMC cathode materials, and the potential of manganese fertilizers. This review aims to find out the effect of structure, synthesis method, and sintering temperature on LMR-NMC cathodes made from manganese sulphate fertilizer to obtain a Li-ion battery with a high specific capacity, more environmentally friendly, has good cycle stability, and a high level of safety and lower production costs.

A gas diffusion electrode was used to implement depolarization of the cathodic process with atmospheric oxygen to improve the production of sodium hypochlorite by electrolysis of an aqueous solution of sodium chloride. As materials for the implementation of depolarization of the cathode process on a porous cathode from the grid, we selected: manganese oxides, cobalt oxides, ruthenium oxides. These oxides are characterized by low overvoltage of the oxygen reaction. Oxides of selected metals were applied to a mesh current lead by thermal decomposition of coating solutionsю. The gas diffusion electrode consisted of a lined titanium current lead, a dispersant of gas made of porous graphite, and an external mesh working element, on which cathodic reactions occurred. The preparation of a catalytically active layer of oxide-metal coatings was carried out by thermal decomposition of coating solutions. This method fully complies with the requirements for oxide-metal electrodes for the electrolysis of aqueous solutions of sodium chloride: the ability to control the composition of the composite coating in a wide range of component concentrations. On the current-voltage cyclic dependences of the cathodic process, for all the materials studied, certain areas of oxygen reduction and combined oxygen reduction and hydrogen evolution are observed. The first section of oxygen reduction is observed to the equilibrium potentials of the hydrogen reaction (approximately –0.42 V). The oxygen reduction rate is small and amounts to 3...5 mA/cm2. There is no difference in the current-voltage dependence due to the high potential sweep speed, which does not lead to oxygen depletion in the case of cathode operation without air supply. In the second section (at potentials, more negative equilibrium potentials of the hydrogen reaction), a significant increase in the rate of the cathodic reaction due to hydrogen evolution is observed. Oxygen, in this case, is reduced at the limiting current density. In the third section (more than –1.5 V), the speed of the cathodic process is almost completely determined by the rate of hydrogen evolution. The effect of air supply to the gas diffusion cathode is observed when comparing the reverse stroke of cyclic current–voltage dependences. On the surface of the steel mesh, an increase in the reverse current is observed in the potential range –1.0 to 0 V. Which indicates an increase in adsorbed particles involved in the cathodic process. As shown earlier, this range of potentials corresponds to the 1st and 2nd sections of the obtained dependences in which the predominant oxygen reduction occurs. Therefore, an increase in the reverse current, with potentials more positive than 1.0 V, can be explained by the effect of oxygen adsorption on the surface of gas-permeable mesh steel cathodes when air is supplied. The addition of hypochlorite ion has practically no effect on the current density in the first and second sections of the current – voltage dependences. A decrease in the cathodic current density is observed at potentials more negative from the equilibrium potential of the hydrogen reaction. This indicates a certain inhibition of the process of hydrogen evolution. In the third section, the current density also decreases. This indicates that 0.08 mol∙dm3 hypochlorite ions do not participate in cathodic reduction. Recommended current density for the studied design of the gas diffusion cathode is 15 mA/cm2 at a temperature of 291...293 K. The cathodic recovery of hypochlorite ions, under these conditions, is reduced by 55...60 %.

Fe-rich alloys have been widely studied as catalyst materials for the cathodic oxygen reduction reaction (ORR) in hydrogen fuel cells, and many have shown high activities. The stability of Fe-rich catalysts has also been researched, and some studies have shown promising results using an accelerated stress test (AST), which uses a potential cycling method. However, for commercial fuel cell applications, such as standby power systems, the catalyst has to tolerate a high potential for a long period, which can not be represented by the AST test. In this paper, the cathode stability of a Fe-rich catalyst was studied using a standby cell potential of 0.9V, a potential shown to be challenging for the competing Pt catalysts. After 1500 hrs of testing, significant morphology changes of both the tested cathode and anode were found due to a Fe leaching process. Other alloy materials, including Ni, Cr, and Mn, were also found leached out along with the Fe species from the catalyst framework. The results are a cautionary note for using Fe based catalysts for AEMFC cathodes.

Microbial electrosynthesis (MES) is a process where bacteria acquire electrons from a cathode to convert CO2 into multicarbon compounds or methane. In MES with Sporomusa ovata as the microbial catalyst, cathode potential has often been used as a benchmark to determine whether electron uptake is hydrogen-dependent. In this study, H2 was detected by a microsensor in proximity to the cathode. With a sterile fresh medium, H2 was produced at a potential of −700 mV versus Ag/AgCl, whereas H2 was detected at −500 mV versus Ag/AgCl with cell-free spent medium from a S. ovata culture. Furthermore, H2 evolution rates were increased with potentials lower than −500 mV in the presence of cell-free spent medium in the cathode chamber. Nickel and cobalt were detected at the cathode surface after exposure to the spent medium, suggesting a possible participation of these catalytic metals in the observed faster hydrogen evolution. The results presented here show that S. ovata-induced alterations of the cathodic electrolytes of a MES reactor reduced the electrical energy required for hydrogen evolution. These observations also indicated that, even at higher cathode potentials, at least a part of the electrons coming from the electrode are transferred to S. ovata via H2 during MES.

Hollow cathodes in electric thrusters normally use an external heater to raise the thermionic electron emitter to emission temperatures. These heaters are a potential single-point failure in the thruster and add a separate power supply to the power processing unit. Heaterless hollow cathodes are attractive for their compact size and potential higher reliability but have only been reliably demonstrated to date in small hollow cathodes capable of discharge currents below around 5 A. A new heaterless LaB6 hollow cathode has been developed that is capable of discharge currents from 5 to 50 A. The cathode configuration extends the gas feed tube at cathode potential part way into the emitting insert region of the cathode. A high-voltage Paschen discharge is struck from the tube to the keeper that heats the tube tip, which then efficiently heats the insert by radiation. This configuration eliminates the arcing observed in prior large heaterless designs that coupled the high-voltage Paschen discharge to the orifice plate or the insert itself. Discharge current–voltage characteristics show that the presence of the tube does not significantly perturb the insert-region plasma. Startup uses a simple 3 min ignition procedure, and voltage traces of the keeper discharge reveal that much of the present tube-radiator’s 100-to-150 W heating power comes from an intermediate thermionic discharge sustained by the tube during the transition between the Paschen discharge and LaB6 insert thermionic regime. This novel heating mechanism enables an unprecedented class of higher-current heaterless hollow cathodes for the next generation of high-power electric propulsion systems.

Cathodic protection, often taught in curricular units, such as corrosion and materials science, is an important subject in the study of chemical engineering. The implementation of lab setups and experimental activities in this field, are core to promoting understanding of the underlying concepts and to developing “hands-on” skills fundamental to the success of future process engineers. This paper reports the influence of different variables on the electrical potential and current behaviors of an educational cathodic protection system operated with a single drainage point. The system comprised a steel bar cathode connected to a zinc sacrificial anode, both placed in aqueous medium. The study variables were the anode area, the cathode diameter, the NaCl electrolyte concentration and the anode placement. Each variable showed a specific influence on the attenuation curves, allowing us to conclude that: (1) increasing the sacrificial anode area, or decreasing the resistivity of the medium, promotes more electronegative potentials on the structure and higher currents; (2) increasing the cathode diameter decreases the protection capacity; (3) positioning the anode in the middle of the cathode lengthwise gives rise to a more balanced potential distribution; and (4), the attenuation curves, both for potential and current, can be successfully predicted using equations based on Morgan and Uhlig’s work. High correlations were obtained between the experimental and modeling data for all the studied variables.

Introduction Water electrolysis is expected a key device to introduce large-scale renewable electricity under management of power grid and electrification of non-electric sector. While alkaline water electrolysis (AWE) systems are well-developed large system, degradation under fluctuated operation with start and stop operation is significant issue to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current, which is leak current through manifold of bipolar alkaline water electrolyzers, and electrode potential behavior of stop operation, and proposed accelerated durability test (ADT) protocol for start and stop operation. Experimental and modeling Figure 1 shows configuration of 4-cells bipolar alkaline water electrolyzer that was consisted with end plates of EP(-) and EP(+), bipolar plates of BP1 to BP3, anodes, separators, and cathodes with principle of reverse current. The end and bipolar plates were made of nickel. Anodes and cathodes were commercially available oxygen and hydrogen electrocatalyst coated nickel mesh electrodes (De Nora Permelec Ltd) with 27.8 cm2 of projected area. Zirfon Perl UTP500 (Agfa) was used for separators. Manifolds were made of Teflon tubes and 15 mL/min of 7 M (= mol/dm3) was circulated for each anolyte and catholyte chambers during measurements. An anode and a cathode set on a bipolar plate. During operation anodes and cathodes are oxidized and reduces, respectively. After stop, the anode and the cathode on a bipolar plate connects both electronically and ionically, so oxidized anode and reduced cathode surface discharges to same potential. In this study, we measured electrode potential and reverse current after 1 h water electrolysis of 80oC at 0.6 A/cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu). Reverse current behavior was analyzed with COMSOL Multiphysics version 5.5 based 2-dimensional model of stack and height direction using experimentally anode and cathode potentials as functions of discharge for anode and cathodes. Results and discussion Figure 2 shows cell performances in the stacks and a picture of the lab-scale zero-gap configuration electrolyzer. All cells in a stack showed almost the same performance. The cell voltage was 2 V at 400 mA/cm2 at 30oC and was 1.8 V at 500 mA/cm2 at 80oC. Therefore, we think all cells and parts work well. Figure 3 shows reverse currents and electrode potentials as a function of time after 1 h electrolysis under 600 mA/cm2 at 30 or 80 oC. Here, the dashed lines in Fig. 3-a) were simulated value and were almost same after 20 s. The measured reverse current increased around 20 s. At this moment, outlet manifolds filled with electrolyte to increase ionic conduction among the chambers, which was not considered in the simulation. After degassed of manifolds, the reverse current decreased with time with the largest reverse current for the BP2. The reverse current at 80oC was significantly larger than that at 30oC. This difference could be explained the dependence of ionic resistance of manifold on temperature. At same moment, anode and cathode potentials on the end plates were almost constant. The anode cathode potentials on the bipolar plates decreased and increased with time, respectively. Both anode and cathode showed significantly potential change region. The final potentials of all electrodes were around 0.9 V vs. RHE. The potential change regions of the electrodes on the BP2 were earlier than others. Here, the anode and cathode potentials as functions of discharge were almost same for the electrode on all bipolar plates. Therefore, the average discharge functions for anode and cathode were treated as characteristics of electrodes of this study. Using this function, reverse current as a function of time could be expressed accurately using the developed model. From this model, reverse current, and electrode potentials as a function of time would be expected with discharge function of each electrode and ionic resistance of manifold. Figure 4 shows that a start & stop operation simulated ADT protocol based on bipolar electrolyzer measurements. We propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1