Cathodic Kinetics Research Articles

Mott-Schottky MXene@WS2 Heterostructure: Structural and Thermodynamic Insights and Application in Ultra Stable Lithium-Sulfur Batteries.

Due to the "shuttle effect" and low conversion kinetics of polysulfides, the cycle stability of lithium sulfur (Li-S) battery is unsatisfactory, which hinders its practical application. The Mott-Schottky heterostructures for Li-S batteries not only provide more catalytic/adsorption active sites, but also facilitate electrons transport by a built-in electric field, which are both beneficial for polysulfides conversion and long-term cycle stability. Here, MXene@WS2 heterostructure was constructed by in-situ hydrothermal growth for separator modification. In-depth ultraviolet photoelectron spectroscopy and ultraviolet visible diffuse reflectance spectroscopy analysis reveals that there is an energy band difference between MXene and WS2 , confirming the heterostructure nature of MXene@WS2 . DFT calculations indicate that the Mott-Schottky MXene@WS2 heterostructure can effectively promote electron transfer, improve the multi-step cathodic reaction kinetics, and further enhance polysulfides conversion. The built-in electric field of the heterostructure plays an important role in reducing the energy barrier of polysulfides conversion. Thermodynamic studies reveal the best stability of MXene@WS2 during polysulfides adsorption. As a result, the Li-S battery with MXene@WS2 modified separator exhibits high specific capacity (1613.7 mAh g-1 at 0.1 C) and excellent cycling stability (2000 cycles with 0.0286 % decay per cycle at 2 C). Even at a high sulfur loading of 6.3 mg cm-2 , the specific capacity could be retained by 60.0 % after 240 cycles at 0.3 C. This work provides deep structural and thermodynamic insights into MXene@WS2 heterostructure and its promising prospect of application in high performance Li-S batteries.

Microstructural evolution and corrosion behavior of constituent particles of AA2024-T3 Al alloy during zirconium conversion coating

The constituent particles of AA2024-T3 Al alloys were identified and their microstructural change after alkaline degreasing, acidic desmutting, and zirconium (Zr) conversion coating was detailed. The constituent particles of AA2024-T3 included Al-Cu-Fe-Mn, θ-Al2Cu, and S-Al2CuMg, and were several micrometers in size. All these three particles were cathodic to the Al matrix after alkaline degreasing and acidic desmutting pretreatment. The OCP evolution in the Zr conversion bath revealed that the conversion coating reactivity of the as-polished AA2024-T3 was promoted after the pretreatment. The polarization test in 0.1 M Na2SO4 + 0.05 M NaCl solution showed that the cathodic kinetics were enhanced after the pretreatment. Subsequent Zr conversion coating inhibited the anodic kinetics but did not alter the cathodic kinetics in chloride solutions. The defects of ZrO2 coating were responsible for the insignificant change in the cathodic activities.

Synergistic dual atomic sites with localized electronic modulation enable high-performance lithium–oxygen batteries

Lithium-oxygen batteries (LOBs) are recognized as promising candidates for next-generation energy storage system technologies due to their high theoretical energy density. Unfortunately, some fundamental issues still constrain the practical implementation of LOBs, including large overpotential, cathode clogging, and poor long-term stability, mainly due to the slow cathodic reaction kinetics. Therefore, the successful construction of rational catalysts becomes an urgent demand for the development of LOBs. Herein, Ni and Mn co-doped MoS2 (Ni/Mn-MoS2) is fabricated via a facile one-pot hydrothermal method and employed as an efficient cathode catalyst for LOBs. The electrochemical results show that the as-prepared Ni/Mn-MoS2 cathode catalyst exhibits low overpotential with a potential gap of 0.78 V, large discharge capacity of 28,195 mAh g−1 at a current density of 100 mA g−1, and enhanced rate capability. The theoretical calculations further reveal that the synergistic effect of Ni and Mn dual atomic sites modulates the electronic structure of catalyst surface, and then enhances the adsorption energy of intermediate product LiO2 and significantly reduces the overpotential for the formation/decomposition of the amorphous discharge product, thereby accelerating the reaction kinetics. This work may provide inspiration for the rational design of MoS2-based materials as highly efficient electrocatalysts for LOBs.

Effects of F− ions on the electrochemical and interface behavior of cathodes in zinc electrowinning

The increasing use of Zn metal in the energy and industrial sectors necessitates a higher level of research into the zinc electrowinning process. In this work, the effects of fluoride ions (F−) in zinc electrolyte on the cathodic kinetics and zinc product quality during zinc electrodeposition was systematically investigated via a series analysis. The results revealed that the addition of F− in the electrolyte showed a polarization effect, with an increase in the apparent cathodic exchange current density increased by 104 orders of magnitude, and a decrease in the zinc deposition overpotential by 46 mV at a concentration of 400 mg/L. However, F− also reduces the hydrogen evolution overvoltage, when the electrolyte contains 400 mg/L F−, the hydrogen evolution overvoltage on aluminum cathode and zinc cathode decreases by 121 mV and 97 mV, respectively. The promoted hydrogen evolution kinetics increases energy consumption and surface porosity. Additionally, F− ions corrode the Al2O3 oxide film on the cathode surface, accelerating the corrosion of the aluminum cathode plate. This results in increased adhesion of zinc deposition to the damaged aluminum substrate, making it difficult to peel off.

Influence of evapotranspiration on wastewater treatment and electricity generation performance of constructed wetland integrated microbial fuel cell

Evapotranspiration (ET) is a natural phenomenon of water loss through plants, which can influence the treatment performance of constructed wetlands integrated with microbial fuel cells (CW-MFC). The influence of ET on the electrochemical performance and treatment performance of CW-MFC in an actual field with real wastewater has never been studied in detail. Thus, this research aims to explore the effects of water loss ascribed by ET on different performance indicators of a CW-MFC fed with municipal wastewater in actual field conditions, for instance, voltage and power generation, internal resistance, and wastewater treatment. During the first 48 h of the operation of CW-MFC, a significant drop in the water level by 336 mm (from 15 mm to 351 mm from the top surface) in the cathode electrode zone due to ET was recorded. This water loss at the cathode enhanced cathodic reduction kinetics by increasing the oxygen saturation at the cathode, thereby improving the voltage generation from 182.5 ± 12.5 mV (first 6 h when the cathode was more water-saturated) to 800 ± 13.47 mV (after 48 h when the cathode was air-saturated due to loss of water), which corresponds to the current and power density of 85.71 mA/m3 and 25.71 mW/m3, respectively. Together with this significant coulombic efficiency (CE) and net energy recovery (NER) of 11.95 % and 2.44 Wh/kg·COD was achieved. The internal resistance of CW-MFC was also noted to decrease from 1000 Ω in the first 6 h to 700 Ω at the end of 48 h. After 48 h of the observation period, the CW-MFC could achieve chemical oxygen demand (COD), ammonium, and phosphate removal efficiency of 80 ± 7.98 %, 73.17 ± 5.01 %, and 75.60 ± 1.65 %, respectively. This study demonstrates a substantial effect on the performance of CW-MFC due to ET water loss in the actual field. Thus, ET is a critical aspect and worth considering for large-scale implementation of CW-MFCs, especially in tropical regions or with dense plantations.

Role of Grain Size and Recrystallization Texture in the Corrosion Behavior of Pure Iron in Acidic Medium

This work investigates the role of grain size and recrystallization texture in the corrosion behavior of pure iron in 0.1 M sulfuric acid solution. Annealing heat treatment was applied to obtain samples with different average grain sizes (26, 53 and 87 µm). Optical microscopy, X-ray diffraction and electron backscatter diffraction techniques were used to characterize the microstructure. The EBSD data analysis showed ferrite phase with no inclusions and very low geometrically necessary dislocation density, indicating strain-free grains constituting all samples. The crystallographic texture analysis of the samples revealed that the 26 µm grain size sample had a high volume fraction of {111} oriented grains parallel to the sample surface, while other samples exhibited nearly random crystallographic texture. The electrochemical results from potentiodynamic polarization and electrochemical impedance spectroscopy showed a decrease in corrosion resistance from 87 µm to 53 µm grain size sample and then an increase for the 26 µm grain size sample. This increase was attributed to the dominant effect of recrystallization texture on the corrosion behavior of the sample. The cathodic hydrogen evolution reaction kinetics was found to play a decisive role in the corrosion behavior of iron.

Microcell and macrocell corrosion of steel bars in reinforced concrete slabs under different corrosive environments and cathode/anode configurations

This paper presents an experimental study and electrochemical mechanisms of microcell and macrocell corrosion kinetics of steel bars in reinforced concrete slabs subjected to three different corrosive environments and three configurations of uncorroded/corroded steel bars. Effects of combined chloride contamination and carbonation were investigated and compared to individual causes either from chloride contamination or carbonation. Under each corrosive environment, two cathode/anode area ratios, as well as steel bars-contact and -noncontact conditions, were tested. As a result, the combined chloride contamination and carbonation induced larger microcell and macrocell corrosion rates than those attacked by solely chloride or solely carbonation. Although a larger cathode/anode ratio increased macrocell current density, it actually decreased microcell rate compared to a smaller ratio. In addition, when corroded steel bars were in contact, microcell and macrocell current densities became larger than those in noncontact samples for all three corrosive environments. Based on the test results, electrochemical mechanisms of both microcell and macrocell corrosion were proposed using thermodynamic theory, anodic and cathodic polarisation kinetics to draw precious insights into the corrosion behaviour under different corrosive environments and cathode/anode ratios.

Ionic liquid route for the corrosion inhibition of Al alloys: the effect of butylammonium nitrate on the corrosion of AA2024-T6

In this work, the effect of an ammonium nitrate ionic liquid on the corrosion susceptibility of an Al-Cu-Mg alloy was investigated. The effect of the nitrate anion and the ammonium cation on the anodic and cathodic kinetics were studied separately using potentiodynamic polarisation testing, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed a significant anodic inhibition, associated with a cation/anion synergy. The cathodic kinetics however increase with the presence of nitrates, associated with nitrate reduction reaction. Conversely, longer alkyl chain seemed to reduce the effect of nitrates. Such findings are promising in the context of developing ecofriendly chromate alternatives.

Influence of the casting process on corrosion behaviour of 2024-T6 aluminium alloy in different conditions of pH and NaCl concentration

ABSTRACT Corrosion behaviour of 2024-T6 castings produced by sand mould and metallic mould has been studied in media with different sodium chloride concentrations and pH values, using electrochemical techniques and scanning electron microscope. Corrosion rates and anodic and cathodic reaction kinetics are detailed to provide a fundamental understanding of the electrochemical behaviour of 2024-T6 at different conditions. The study shows a different corrosion mechanism depending on the pH. At pH 12, the more negative values of E corr confirmed that the alkalinisation of aluminium incites the dissolution of the Al substrate. The effect of chloride concentration is reflected in shifts of E corr towards more negative values. The research on the effect of the used mould demonstrates that the impact of the casting process in the cooling rate affects the pitting corrosion resistance.

Oxygen scavenging activity of smart colophony microcapsules containing nitrite corrosion inhibitors for steel reinforced concrete

In this study, the electrochemical performance of microcapsules (MCs) containing NaNO2corrosion inhibitors for steel reinforcements was studied in 0.6 M chloride contaminated simulated concrete pore solutions (SCPS) with varying pH for a period of 28 days. The corrosion inhibition was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The polarization results for the MC samples showed improved corrosion resistance, with anicorrof 2.54 ×10–6A/cm2after 28 days exposure in SCPS. Oxygen scavenging activity from the MCs was observed by reduced cathodic kinetics, displaying decreased cathodic exchange current densities of 2.66 ×10−8A/cm2, thus imparting cathodic inhibition in conjunction with anodic corrosion inhibitors. The microcapsules additionally displayed improvement over free NaNO2inhibitors after sufficient release time. The decrease in cathodic and anodic kinetics, along with the improved corrosion resistance, show a dual synergistic corrosion inhibition of the NaNO2loaded colophony MC.

A Comprehensive Study on Air-Cathode Limitations and Its Mitigation Strategies in Microbial Desalination Cell—A Review

Microbial desalination cells (MDCs) are promising bioelectrochemical systems for desalination using the bacteria-generated electricity from the biodegradation of organic wastes contained in the wastewater. Instead of being a sustainable and eco-friendly desalination technology, the large-scale application of MDC was limited due to the high installation cost of the metal-catalyst-coated cathode electrode and the poor performance of the cathode in long-term operation due to catalyst fouling. Such cathodic limitations have hindered its large-scale application. The cathodic limitation has arisen mainly because of three losses, such as (1) Ohmic loss, (2) mass transfer loss, and (3) activation loss. The catalyst-assisted cathodic reduction reaction is an electrochemical surface phenomenon; thereby, the cathode’s surface charge transfer and thermodynamic efficiency are crucial for reaction kinetics. This review article aims to provide an overview of the MDC process, performance indicators, and summarizes the limiting factors that could hinder the process performance. Then, the article represented a comprehensive summary of the air-cathodic limitations and the mechanisms applied to improve the air-cathodic limitations in MDC to enhance the cathodic reaction kinetics through cathode surface modification through catalysts. The study is significantly different from other review studies by the precise identification and illustration of the cathodic losses and their mitigation strategies through surface modification. The details about the role of photocatalysts in the minimization of the cathode losses and improvement of the performance of MDC were well presented.

Evolution of Surface Oxides of UNS S13800 during Cathodic Polarization in Chloride Solutions

Solutions arising from atmospheric processes can have varying chloride concentrations, often higher than seawater as salt deposits accumulate in thin layer electrolytes. Understanding the corrosion behavior of stainless-steel fastener components is important to predicting its behavior in a galvanic couple with less noble materials. Here we have focused on the cathodic kinetics of UNS S13800 stainless steel over a range of chloride concentration electrolytes. The different oxides formed under these varying conditions are studied using surface analytical techniques. This information is then used to inform a model for fitting of the potentiodynamic polarization curves. The evolving composition of the surface oxide affects the polarization curve in the activation region of the oxygen reduction reaction. This additional cathodic current is accounted for in the model and the different reaction components of the polarization curve are extracted and analyzed.AcknowledgmentsThe U.S. Naval Research Laboratory sponsored this project as part of their base program. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, the Department of Defense, or the U.S. government

Dual‐Network Structured Hydrogel Electrolytes Engaged Solid‐State Rechargeable Zn‐Air/Iodide Hybrid Batteries

AbstractAs a key component of batteries, the electrolyte determines the ion transport and interface chemistry of the cathode and anode. In this work, we develop a dual‐network structured hydrogel electrolyte composed of polyacrylamide (PAM), sodium alginate (SA) and potassium iodide (KI) for solid‐state zinc‐air/iodide hybrid batteries. The assembled hybrid battery shows excellent renewability and a long cycling life of 110 h with a high energy efficiency of 80 %. The ion‐crosslinked dual‐network structure endows the material with improved mechanical strength and increased ionic conductivity. More importantly, the introduction of iodine species not only offers more favorable cathodic kinetics of iodide/iodate redox than oxygen electrocatalysis but also regulates the solvation structure of zinc ions to ensure better interface stability. This work provides significant concepts for developing novel solid‐state electrolytes to realize high‐performance energy devices and technologies.

Dual-Network Structured Hydrogel Electrolytes Engaged Solid-State Rechargeable Zn-Air/Iodide Hybrid Batteries.

As a key component of batteries, the electrolyte determines the ion transport and interface chemistry of the cathode and anode. In this work, we develop a dual-network structured hydrogel electrolyte composed of polyacrylamide (PAM), sodium alginate (SA) and potassium iodide (KI) for solid-state zinc-air/iodide hybrid batteries. The assembled hybrid battery shows excellent renewability and a long cycling life of 110 h with a high energy efficiency of 80 %. The ion-crosslinked dual-network structure endows the material with improved mechanical strength and increased ionic conductivity. More importantly, the introduction of iodine species not only offers more favorable cathodic kinetics of iodide/iodate redox than oxygen electrocatalysis but also regulates the solvation structure of zinc ions to ensure better interface stability. This work provides significant concepts for developing novel solid-state electrolytes to realize high-performance energy devices and technologies.

In-situ electrochemical study of chalcopyrite pressure oxidation leaching from 110 °C to 150 °C under saturated vapor pressure

Pressure oxidation leaching behavior of chalcopyrite in sulfuric acid solution from 110 °C to 150 °C were investigated by in-situ electrochemical methods. Leaching experiments under saturated vapor pressure conditions were used to simulate the anoxic environment that may be encountered in industrial applications. Scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the morphology and the chemical status of chalcopyrite surface. Results show that the copper extraction was increased with the increase of leaching temperature. Under the optimal leaching conditions under saturated vapor pressure, the copper and iron extraction are 8.3% and 29.8%, respectively. When the temperature increased from 110 °C to 150 °C, the self-corrosion potential and electrochemical reaction resistance firstly increased and then decreased. In contrast, the resistance of the passive film was always increased with the increase of temperature. The electrochemical study results indicated that the increase in temperature affected the oxidation of chalcopyrite by altering the kinetics of the cathodic reaction and the anodic passivation. Both the self-corrosion current density ( i corr ) and rate constant were affected by the reduction of Fe(III). The XPS results show that elemental sulfur and H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) were the main leaching solid products. The formation of H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) not only caused a decrease in cathodic reaction kinetics, but also increased the resistance of mass transfer process. Due to the faster release of iron, copper-rich sulphides were formed, which mixed with the elemental sulfur and/or H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) led to coverage of the chalcopyrite surface.

Corrosion resistance and anomalous hydrogen evolution in chloride containing solutions of extruded cast and powder metallurgical Mg-1Zn alloy

The corrosion resistance and anomalous hydrogen evolution of extruded cast and powder metallurgical (PM) Mg-1Zn alloy were investigated. Potentiodynamic polarization revealed that the PM Mg-1Zn alloy actively corroded at the OCP due to enhanced cathodic kinetics, whereas the cast Mg-1Zn alloy remained spontaneously passive. HE measurements confirmed that the cast Mg-1Zn alloy exhibited lower HE rates than the PM Mg-1Zn alloy. Rp values for the PM Mg-1Zn alloy were remarkably lower than for the cast Mg-1Zn alloy. The anomalous HE rates were higher for the PM Mg-1Zn alloy with over 90% of the charge ratio associated with anomalous HE.

Regulating Lithium Salt to Inhibit Surface Gelation on an Electrocatalyst for High-Energy-Density Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have great potential as high-energy-density energy storage devices. Electrocatalysts are widely adopted to accelerate the cathodic sulfur redox kinetics. The interactions among the electrocatalysts, solvents, and lithium salts significantly determine the actual performance of working Li-S batteries. Herein, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a commonly used lithium salt, is identified to aggravate surface gelation on the MoS2 electrocatalyst. In detail, the trifluoromethanesulfonyl group in LiTFSI interacts with the Lewis acidic sites on the MoS2 electrocatalyst to generate an electron-deficient center. The electron-deficient center with high Lewis acidity triggers cationic polymerization of the 1,3-dioxolane solvent and generates a surface gel layer that reduces the electrocatalytic activity. To address the above issue, Lewis basic salt lithium iodide (LiI) is introduced to block the interaction between LiTFSI and MoS2 and inhibit the surface gelation. Consequently, the Li-S batteries with the MoS2 electrocatalyst and the LiI additive realize an ultrahigh actual energy density of 416 W h kg-1 at the pouch cell level. This work affords an effective lithium salt to boost the electrocatalytic activity in practical working Li-S batteries and deepens the fundamental understanding of the interactions among electrocatalysts, solvents, and salts in energy storage systems.

Addition of niobium in Fe-13Cr-4.5Al-2Mo alloy used as ATF cladding: Effect on high temperature water corrosion and in-situ electrochemistry

Niobium addition in candidate accident tolerant fuel (ATF) cladding FeCrAl alloy has received much attention, but its effect on high temperature water corrosion behavior has not been revealed. Four alloys with different Nb content (0 wt%, 0.5 wt%, 1.0 wt% and 1.5 wt%) based on Fe-13Cr-4.5Al-2Mo model alloy were designed, and the corrosion behavior was investigated by in-situ electrochemistry and microscopy. The in-situ electrochemistry analyses, including open circuit potential (OCP), polarization and electrochemical impedance spectrum, were carried out in 360 °C/19.0 MPa lithiated and borated water connected with a loop system to monitor the water chemistry. The oxide films formed after immersion for 85 days were deeply investigated by focused ion bombarding and transmission electron microscopy. Results have shown that OCP decreased with elevated temperature and corrosion potential increased with time. FeCrAl alloys have satisfactory corrosion resistance because of small corrosion currents and thin oxide films. Only monolayer multicrystal spinel oxide forms on FeCrAl alloys. Slight Nb addition (0.5 wt% and 1.0 wt%) benefits the corrosion resistance due to relatively large impedance of oxide and delayed oxidation of Fe2Nb particles. Porosities with Fe depletion were spotted in oxide and especially severe in 1.5 wt%-Nb alloy. Cathodic Tafel kinetics and corrosion mechanisms of FeCrAl were further discussed.

Numerical simulation of extremely severe corrosion of the STK400 graded steel pipe pile in Southern Vietnam’s brackish environment: effects on macrocell corrosion of seawater flow and tide

In the recent work, a field test in which an STK400 steel pipe pile was vertically driven into the sea bed was conducted in Southern Vietnam’s brackish environment. After 5 years of exposure, the steel pipe pile was uniformly corroded in the immersion zone but two penetrated holes (formed a 152° central angle) appeared near the low water level. This severe corrosion can not be explained experimentally. Therefore, two numerical models have been individually built to calculate the corrosion distribution on a steel pipe pile surface. The results of these models help to explain this observation. The differential aeration due to the tidal condition and seawater flow is confirmed to be the cause of this field test observation. The first model accounting for the effects of tide shows that a macroscopic corrosion cell (along the pipe length) is formed. The cathodic kinetics are only strongly enhanced near the seawater surface (which changes over time and belongs to the tidal condition) while the rest is controlled by the limited-diffusion phenomenon. Therefore, a cathode is formed underneath the seawater surface and receives a protective current from the deeper steel surface (acts as an anode) where these two holes may appear. The second model considering the effects of seawater flow successfully locates two highly active anodic areas being in agreement with the position of the two penetrated holes observed in the field test.

Insights into the influence of oxide inclusions on corrosion performance of additive manufactured magnesium alloys

The corrosion performance of binder jet additive samples is compared with cast samples through potentiodynamic polarization in Na2SO4 solution. Higher zinc levels in the magnesium matrix and the presence of MgO within the microstructure of the binder jet printed alloy contribute to increases in the anodic and cathodic kinetics, respectively. It is proposed that electron inhomogeneity at the Mg/MgO interface in the binder jet printed alloy is the source of the catalytic activity of the hydrogen evolution reaction. The removal of MgO inclusions suppressed the cathodic reaction relative to the large increase in kinetics seen in similarly treated cast samples.