Local Electrochemical Reactions Research Articles

Corrosion behavior of 70/30 cupronickel in electrolytic seawater antifouling environment

Available chlorine is most commonly used in seawater cooling systems to eliminate biofouling. The corrosion behavior of 70/30 cupronickel alloy after exposure to seawater with different concentrations of available chlorine was studied by electrochemical and immersion tests. The electrochemical measurements show that 100 ppm available chlorine accelerates the corrosion of 70/30 cupronickel alloy in seawater. The corrosion rate of 70/30 cupronickel sample in seawater with 100 ppm available chlorine is 3–4 times higher than that in seawater with 0–10 ppm available chlorine. Scanning Kelvin probe (SKP) and scanning vibrating electrode technique (SVET) results demonstrate that the local electrochemical reaction of 70/30 cupronickel alloy is more active after soaking in seawater with 100 ppm available chlorine. Energy dispersive spectroscopy (EDS) results reveal that Cl element in the corrosion products is enriched after exposure to seawater with 100 ppm available chlorine. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the corrosion product of 70/30 cupronickel sample contains more Cu2(OH)3Cl after being immersed in seawater with 100 ppm available chlorine.

Contributions to a More Realistic Characterization of Corrosion Processes on Cut Edges of Coated Metals Using Scanning Microelectrochemical Techniques, Illustrated by the Case of ZnAlMg-Galvanized Steel with Different Coating Densities.

Corrosion processes at cut edges of galvanized steels proceed as highly localized electrochemical reactions between the exposed bulk steel matrix and the protective thin metallic coating of a more electrochemically active material. Scanning microelectrochemical techniques can thus provide the spatially resolved information needed to assess the corrosion initiation and propagation phenomena, yet most methods scan cut edge sections as embedded in insulating resin to achieve a flat surface for scanning purposes. In this work, the galvanized coatings on both sides of the material were concomitantly exposed to simulated acid rain while characterizing the cut edge response using SECM and SVET techniques, thereby maintaining the coupled effects through the exposure of the whole system as rather realistic operation conditions. The cut edges were shown to strongly promote oxygen consumption and subsequent alkalization to pH 10-11 over the iron, while diffusion phenomena eventually yielded the complete depletion of oxygen and pH neutralization of the nearby electrolyte. In addition, the cathodic activation of the exposed iron was intensified with a thinner coating despite the lower presence of sacrificial anode, and preferential sites of the attack in the corners revealed highly localized acidification below pH 4, which sustained hydrogen evolution at spots of the steel-coating interface.

Improving insight into the localized electrochemical Volmer reaction based on surface enhanced Raman spectroscopy and collisions.

An operando EC-SERS strategy was successfully developed for monitoring the Volmer reaction based on dynamic collisions. Its feasibility and universality were verified, and it provided a promising approach for visualizing a localized surface reaction.

Analysis of mass transfer characteristics in a planar solid oxide fuel cell with a chaotic flow channel

The flow channel design is crucial for the heat and mass transfer of reactants in a solid oxide fuel cell (SOFC), which ultimately affects the overall performance of the cell. To improve the gas transport characteristics and temperature uniformity, a chaotic flow channel with orthogonal corrugation is adopted for the design of a planar SOFC stack, and the influence of different wave parameters is evaluated. The results show that the chaotic flow channel induces secondary flow through the superposition of orthogonal waves, which reduces the low-oxygen region and enhances the local electrochemical reaction. The output power is improved in the chaotic flow channel by increasing the amplitude or decreasing the wavelength. The output power density with amplitude of 0.3 mm and wavelength of 1.2 mm at 0.5 V is increased by about 25.16 %. Meanwhile, the effective mass transfer coefficient and mass transfer efficiency is enhanced by 148 % and 378 %, respectively. Additionally, the chaotic structure improves the uniformity of oxygen and temperature. This study helps to improve the understanding of the gas transport processes within the flow channel and provides a basis for the design and optimization of SOFC flow channels.

Additive Manufacturing of Multi‐Metal Microstructures by Localized Electrochemical Deposition Under Hydrodynamic Confinement

AbstractThis study presents a device and method for multi‐metal printing of microscale structures. The method is based on combining hydrodynamic confinement of electrolytes with localized electrochemical deposition (HLECD), allowing rapid switching of the deposited metal. The device used in HLECD integrates a micro‐anode on a vertical microfluidic chip containing two open‐ended channels that control the flow of electrolytes surrounding the anode. When placed on top of a conducting surface, a localized electrochemical reaction is initiated, wherein the deposited metal composition is dictated by the electrolyte in the confinement. A range of electrolytes, which are used to deposit copper, tin, silver, and nickel, are used to fabricate multiple structures involving more than 60 material changes within a single printing process. The structures are analyzed using electron microscopy, showing the ability to achieve sharp transitions between pure metals. The constant replenishment of electrolytes also eliminates the problem of ion depletion commonly occurring in localized electrochemical deposition, and enables printing rates that are nearly an order of magnitude greater.

Static Stress Analysis of Membrane Electrode Assembly (MEA) and Gasket in Proton Exchange Membrane Fuel Cell Stack Assembly Pressure

The proton exchange membrane fuel cell (PEMFC) system was an electrochemical device that generates electricity through the reaction of hydrogen and oxygen without combustion. Proton Exchange Membrane (PEM) stacks typically consisted of components combined into one unit and equipped with suitable clamping torque. This was to prevent reactant gas leakage and minimize the contact resistance between the gas diffusion medium and the bipolar plate. The combined components consisted of a bipolar plate with a flow field, current collector, membrane electrode assembly (MEA), endplate, and gasket. PEMFC performance was measured concerning its power output, which depends on temperature and the operating pressure. Various efforts had been made to determine the optimal compaction pressure and its distribution through simulations and experiments. Therefore, this research analyzed the static stress of membrane electrode assembly (MEA) and gasket in PEMFC stack assembly pressure. The components’ geometric dimensions and mechanical properties, such as endplates, current collectors, bipolar plates, MEAs, and gaskets, were combined for electricity. Pressure-sensitive film (Fuji measure film prescale) was also used to visualize contact pressure distribution between the MEA and the bipolar plate. The result showed that the color variation of the pressure film indicates the exact distribution of pressure entering the stacking design and the contact image. In conclusion, the detailed contact pressure distribution was an important influence on heat transfer processes and local electrochemical reactions in cell stacks.

Site-selective heat boosting electrochemiluminescence for single cell imaging.

In operando visualization of local electrochemical reactions provides mechanical insights into the dynamic transport of interfacial charge and reactant/product. Electrochemiluminescence is a crossover technique that quantitatively determines Faraday current and mass transport in a straightforward manner. However, the sensitivity is hindered by the low collision efficiency of radicals and side reactions at high voltage. Here, we report a site-selective heat boosting electrochemiluminescence microscopy. By generating a micron-scale heat point in situ at the electrode-solution interface, we achieved an enhancement of luminescence intensity up to 63 times, along with an advance of 0.2 V in applied voltage. Experimental results and finite element simulation demonstrate that the fundamental reasons are accelerated reaction rate and thermal convection via a photothermal effect. The concentrated electrochemiluminescence not only boosts the contrast of single cells by 20.54 times but also enables the site-selective cell-by-cell analysis of the heterogeneous membrane protein abundance. This electrochemical visualization method has great potential in the highly sensitive and selective analysis of local electron transfer events.

Corrosion failure analysis of the heat exchanger in a hot water heating boiler

The corrosion failure of the heat-exchanger made of 20G steel in a hot water heating boiler was investigated. The morphology and phase compositions of the corrosion products were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM) with energy disperse spectroscopy (EDS). The results showed that the boiler feed water did not meet the water quality standard, which contained excessive ion concentrations of Ca and Mg and dissolved oxygen content. At the surface of failed tubes, loose corrosive products containing numerous cracks provided micro-channels for Cl- diffusion into the matrix of 20G steel, thus leading to the local electrochemical reaction. This continuous and Cl-induced electrochemical erosion at some positions led to a vicious cycle which caused more severe damage to the tube, finally resulting in a perforation failure of the tube. To avoid this kind of accident happening, some suggestions are given in this paper.

Assessing the Drawbacks and Benefits of Ion Migration in Lead Halide Perovskites.

Since the inception of the unprecedented rise of halide perovskites for photovoltaic research, ion migration has shadowed this material class with undesirable hysteresis and degradation effects, limiting its practical implementations. Unfortunately, the localized doping and electrochemical reactions triggered by ion migration cause many more undesirable effects that are often unreported or misinterpreted because they deviate from classical semiconductor behavior. In this Perspective, we provide a concise overview of such effects in halide perovskites, such as operational instability in photovoltaics, polarization-induced abnormal external quantum efficiency in light-emitting diodes, and energy channel shift and anomalous sensitivities in hard radiation detection. Finally, we highlight a unique use case of exploiting ion migration as a boon to design emerging memory technologies such as memristors for information storage and computing.

Numerical Simulation of Crevice Corrosion of Stainless Steel–Titanium in NaCl Solution

A multiphysics model based on the finite element method was adopted, emphasizing a deeper insight into the rarely studied crevice corrosion behavior of stainless steel and titanium overlapping. The model takes into account damage due to corrosion inside the crevice, different species transportation, local electrochemical reactions, homogeneous reactions in the electrolyte, and formation of a corrosion product and its influence on electrochemical reaction. The simulation results show that the location of the greatest attack for stainless steel is at the crevice opening; this finding is consistent with the IR drop theory. The potential increases gradually from the tip to the opening of the crevice, and the current changes smoothly following a sharp rise at the opening. The minimum and maximum values of pH and Cl− concentration are both in the middle and opening of the crevice. The influence of the crevice size on corrosion is also discussed in detail.

Studies on the effect of flow configuration on the temperature distribution and performance in a high current density region of solid oxide fuel cell

• Three different flow configurations of solid oxide fuel cell have been compared. • The temperature distribution at 6000 A/m 2 were analyzed. • In counter-flow, the most uniform temperature distribution was formed. • The power density is 5% higher in counter-flow than the other configurations. • Counter-flow presents the best efficiency of up to 3.35%. The effect of temperature distribution on the performance of solid oxide fuel cells (SOFCs) is analyzed for various channel designs in a high current density region. By considering heat accumulation due to local electrochemical reactions and cooling due to flow patterns, the heat distributions in three flow configurations (co-flow, counter-flow, and cross-flow) are analyzed, with the most appropriate channel in the high power region selected. The average operating temperature of the cell is the highest for the counter-flow configuration and the lowest for co-flow. The temperature of the counter-flow configuration is approximately 10 K higher than that of co-flow. The temperature distribution of counter-flow configuration, however, is the most uniform among different flow patterns. The maximum temperature difference in the counter-flow channel is approximately 8 K, but that in co-flow is approximately 22 K. Furthermore, the performance of the cell using the counter-flow configuration is the best in that it shows 5% higher power density and 3.35% higher system efficiency than the other flow configurations. Therefore, the counter-flow configuration is superior at high power because it has the lowest temperature gradient and the best cell performance. This paper contributes to the commercialization of the fuel cell by presenting appropriate parameters for temperature regulation and suitable flow configuration for operation at high power.

Enhanced Long-Term Reliability of Seal DeltaSpot Welded Dissimilar Joint between 6061 Aluminum Alloy and Galvannealed Steel via Excimer Laser Irradiation.

Structural-adhesive-assisted DeltaSpot welding was used to improve the weldability and mechanical properties of dissimilar joints between 6061 aluminum alloy and galvannealed HSLA steel. Evaluation of the spot-weld-bonded surfaces from lap shear tests after long-term exposure to chloride and a humid atmosphere (5% NaCl, 35 °C) indicated that the long-term mechanical reliability of the dissimilar weld in a corrosive environment depends strongly on the adhesive–Al6061 alloy bond strength. Corrosive electrolyte infiltrated the epoxy-based adhesive/Al alloy interface, disrupting the chemical interactions and decreasing the adhesion via anodic undercutting of the Al alloy. Due to localized electrochemical galvanic reactions, the surrounding nugget matrix suffered accelerated anodic dissolution, resulting in an Al6061-T6 alloy plate with degraded adhesive strength and mechanical properties. KrF excimer laser irradiation of the Al alloy before adhesive bonding removed the weakly bonded native oxidic overlayers and altered the substrate topography. This afforded a low electrolyte permeability and prevented adhesive delamination, thereby enhancing the long-term stability of the chemical interactions between the adhesive and Al alloy substrate. The results demonstrate the application of excimer laser irradiation as a simple and environmentally friendly processing technology for robust adhesion and reliable bonding between 6061 aluminum alloy and galvannealed steel.

A Variety of Functional Devices Realized by Ionic Nanoarchitectonics, Complementing Electronics Components

AbstractTo realize the continuous development of information and communication equipment, it is also important to develop devices with new operating principles that overcome the functional and performance limitations of conventional electronics devices, such as transistors made of semiconductor materials. One group of devices that hold this promise is nanoionics devices that operate by using local ion transport and electrochemical reaction in solids. A number of nanoionics devices that control nanoelectrochemical phenomena through the use of ionic nanoarchitectonics have been created. Here the use of ionic nanoarchitectonics to locally control ion transport and electrochemical reactions through the use of ion conductors or mixed conductors as device materials is described. Further, the structures of nanoionics devices created by using the nanoarchitectonics, as well as their various electrical, magnetic and optical functionalities are introduced. It is expected that such nanoionics devices will complement conventional electronics devices, and make possible the further development of information and communication technologies.

Response and Implication of NASICON Solid-State Electrolytes to Local Electrical Stimulation: From Surface Engineering to Interfacial Manipulation.

The surface feature of solid electrolytes fundamentally governs their own physical properties and significantly affects the interaction with the electrode materials. The evaluation of interfacial contact between the electrolyte and the metallic anode is largely relied on the macroscopic contact angle measurement, which is influenced by the intrinsic wettability and the microstructure of the electrolyte. In this work, the surface chemistry of the solid electrolyte is first regulated via facile thermal treatments. Then, scanning probe microscopy (SPM)-based techniques are comprehensively adopted to study the interaction between the electrolyte and metallic anode at the nanoscale. By manipulating the overpotential applied on the SPM tip, the mobile sodium ions at the subsurface of the solid electrolyte can be extracted toward the surface, and the eventual topography of the products is deliberately correlated with the sodium wettability. In this context, the impact of surface treatment on the sodium wettability of the surface layer is systematically evaluated based on the topographic evolution at the nanoscale. Furthermore, the local electrochemical reaction dynamics is revealed by correlating the surface ionic activity and current-voltage (I-V) curves. This work presents a new methodology to effectively evaluate the sodium wettability of the solid electrolyte, and these findings can provide meaningful implications to the surface engineering of ceramic electrolytes for high-performance solid-state batteries.

Effects of biochar nanoparticles on anticorrosive performance of zinc-rich epoxy coatings

Biochar nanoparticles (BCN) derived from spruce wood and wheat straw were prepared, characterized and incorporated into zinc-rich epoxy coatings, with the aim of improving the zinc powder utilization and the anticorrosion performance. Formulations with different BCN and commercial carbon black dosages (0.4 wt%, 0.8 wt% and 1.6 wt%) were compared to a zinc-rich epoxy paint (ZRP) without carbon addition. After immersion and salt spray exposure, coated steel panels were characterized with optical, electrochemical and spectroscopy techniques to evaluate the anticorrosive performance. BCN and carbon black addition enhanced the local electrochemical reactions and the barrier effects were promoted by an increased amount of zinc corrosion products (Zn5(OH)8Cl2 and ZnCO3). The formulation with 0.8 wt% of spruce wood BCN performed equivalently well compared to the ones with carbon black. The degraded area and rust accumulation around the artificial scribe for the formulation with 0.8 wt% of spruce wood BCN were 29.8% and 27.8% less than ZRP, respectively, which is attributed to the good electrical conductivity and high specific surface area of spruce wood char. These results suggest a promising and sustainable option for improving the anticorrosive performance of zinc-rich epoxy coatings by the incorporation of BCN.

In situ and operando force‐based atomic force microscopy for probing local functionality in energy storage materials

AbstractElectrochemical energy storage is the key enabling component of electric vehicles and solar‐/wind‐based energy technologies. The enhancement of energy stored requires the detailed understanding of charge storage mechanisms and local electrochemical and electromechanical phenomena over a variety of length scales from atoms to full cells. Classical electrochemical techniques, such as voltammetry, represent the macroscopic electrochemical properties, and consequently do not allow to extract important information about local electrochemical reactions, ions adsorption, intercalations, and transport. Understanding, controlling, and tuning the local electrochemical functionalities in functional energy materials require in situ/operando techniques which limit the use of structural and functional characterization techniques that provide local information. Here, force‐based atomic force microscopies (AFMs) have provided novel insights into locally probing electrochemical mechanisms on tens of nanometer and even molecular length scales and provide a viable pathway to probe electrochemical processes in situ/operando. In this review, we highlight the contributions in the development and application of force‐based AFM methods to elucidate the local charge storage mechanism in a variety of energy‐related materials. We will focus in particular on methods or AFM modalities in a liquid electrolyte environment.

High spatial resolution temperature profile measurements of solid-oxide fuel cells

Temperature gradients resulting from local electrochemical reactions, current distribution and geometry of gas flow channels in solid oxide fuel cells (SOFCs) create thermal stresses, localized thermophysical property gradients and uneven property evolution, contributing to SOFC degradation. This paper presents a new method to perform temperature measurements (up to 800 °C) at high spatial resolutions to monitor the operation of SOFCs. Using femtosecond laser irradiation, distributed fiber sensors were hardened for high temperature environment applications. Distributed fiber sensors were embedded in interconnected plates using an additive manufacturing method to perform temperature measurements with 4-mm spatial resolution during the operation of a planar fuel cell. The measurement revealed the impact of various H2 fuel concentrations and current loads have on temperature profiles of the SOFC tested. Temperature variation on the anode side was found to be less than 5 °C, and 3 °C on the cathode side. The measurements were compared to results from a multiphysics fuel cell performance model simulating similar conditions. These simulations predicted similar temperature gradients, indicating the experimental data obtained is reasonable. The model also predicts that the effect of the embedded sensor has on the local temperature will be minimal and that the gradient of temperature in the gas channels will be captured despite the separation between the sensor and the gas flow. The high spatial resolution data harnessed by these distributed fiber sensors provides experimental support for model-based design and optimization to improve the operational efficiency and longevity of solid oxide fuel cells and fuel cell assemblies.

Heterogeneous optoelectronic characteristics of Si micropillar arrays fabricated by metal-assisted chemical etching

Recent progress achieved in metal-assisted chemical etching (MACE) has enabled the production of high-quality micropillar arrays for various optoelectronic applications. Si micropillars produced by MACE often show a porous Si/SiOx shell on crystalline pillar cores introduced by local electrochemical reactions. In this paper, we report the distinct optoelectronic characteristics of the porous Si/SiOx shell correlated to their chemical compositions. Local photoluminescent (PL) images obtained with an immersion oil objective lens in confocal microscopy show a red emission peak (≈ 650 nm) along the perimeter of the pillars that is threefold stronger compared to their center. On the basis of our analysis, we find an unexpected PL increase (≈ 540 nm) at the oil/shell interface. We suggest that both PL enhancements are mainly attributed to the porous structures, a similar behavior observed in previous MACE studies. Surface potential maps simultaneously recorded with topography reveal a significantly high surface potential on the sidewalls of MACE-synthesized pillars (+ 0.5 V), which is restored to the level of planar Si control (− 0.5 V) after removing SiOx in hydrofluoric acid. These distinct optoelectronic characteristics of the Si/SiOx shell can be beneficial for various sensor architectures.

A multiphysics model for studying transient crevice corrosion of stainless steel

The transient crevice corrosion behavior of 304 stainless steel in NaCl solution has been investigated by a multiphysics coupling model. The model considers local electrochemical reactions, transport of different species, and homogeneous reactions. The moving mesh method is used to obtain the geometrical change of the crevice wall with time due to corrosion. The level set method is employed to quantitatively describe the influence of the precipitation process on electrochemical reactions. The transient crevice corrosion morphology, potential and current distributions, and pH and chloride ion concentration distributions are obtained by simulation. The effect of crevice geometry factors on the corrosion process is also discussed. The simulation results are in good agreement with the experiments, showing that the model has high reliability.

Dynamically visualizing battery reactions by operando Kelvin probe force microscopy

Energy storage devices using electrochemical reactions have become an integral part of our daily lives, and further improvement of their performance is highly demanded. An important task for this purpose is to thoroughly understand the electrochemical processes governing their chemistry. Here we develop a method based on Kelvin probe force microscopy that enables dynamic visualization of changes in the internal potential distribution in an operating electrochemical device and use it to characterize an all-solid-state lithium ion battery. Observation of the cathode composite regions during a cyclic voltammetry operation reveals differences between the behavior of local electrochemical reactions in the charge and discharge processes. Based on careful inspection of the results, we show that the difference arises from a change in the state of an electronic conductive path network in the composite electrode. Our method provides new insights into the local electrochemical reactions during electrochemical operation of devices.