Electrochemical Impedance Measurements Research Articles

Stabilization of the stainless-steel interface using sequentially deposited Al2O3 nano films using atomic layer deposition (ALD) technique

Atomic layer deposition (ALD) has been an important surface processing technique of materials of important applications. In the present investigation aluminum oxide thin films are generated using ALD technique (ALD-Al2O3). The ALD-Al2O3 films are formed over SS304 substrates with thicknesses of 20, 75 and 100 nm and the corrosion investigations are carried out using polarization and impedance measurements. The neutron reflectivity measurements are carried out to measure the thickness and surface roughness of the film. The corrosion property of SS304 observed to be reduced on ALD deposition which has been evident from the polarization measurements and supported by the electrochemical impedance measurements. The ennoblement in the corrosion potential has been observed due to the ALD-Al2O3 film formation over the SS304 surface. The polarization resistance remained high even at high applied anodic potential of 0.7 V, the protection remained stable even at an elevated temperature of 60οC.The investigation supports the primary objective of the important role of the protection of material through thin ALD-Al2O3 protective films.

Effects of thickness of CeO2-added Au electrodes of YSZ-based gas sensors on VOC-sensing properties

Yttria-stabilized zirconia (YSZ)-based gas sensors attached with CeO2-added Au sensing electrodes (SEs) were fabricated by using spin-coating method (the number of individual spin-coating (and subsequent drying) cycles (x): 5, 10, 15), and their toluene-sensing properties were investigated in this study. The 24 wt% CeO2-added SE fabricated with the fewest spin-coating cycles (x: 5) showed that the island-like agglomerated particles (50–100 nm in diameter) were isolated with each other. The increase in the x value increased the size of the agglomerated particles as well as reduced the distance among them. On the other hand, the thickness of the 32 wt% CeO2-added Au SEs increased in columnar form with an increase in the x value. Toluene response of the sensors using the 24 wt% CeO2-added Au SE decreased with an increase in the SE thickness, while that of the sensors using the 32 wt% CeO2-added Au SE increased with an increase in the SE thickness. Electrochemical impedance measurement elucidated the increase in the length of triple phase boundaries with an increase in the SE thickness irrespective of the amount of CeO2 in the SEs. It is also confirmed that the morphological differences originating from the amount of CeO2 significantly affect the dependences of the toluene responses of all sensors on the SE thickness.

Construction of Co3O4/Bi5O7I heterojunction derived from ZIF-67/BiOI with enhanced photodegradation ability

Recently, the degradation of expired and unused antibiotics has been a great concern for human health, and it has become a serious environmental hazard. Photocatalysis technology has treated the most promising ways to degrade antibiotics in the environment with high efficiency and low cost. A series of Co3O4/Bi5O7I composites were successfully synthesized via the calcination method derived from Zeolitic imidazolate frameworks-67 and Bismuth oxyiodide, and chatacerized by spectroscopic and also X-ray diffraction (XRD) processes. Co3O4/Bi5O7I composites exhibited enhanced photocatalytic performance for tetracycline degradation, which is about 6 times higher than that of the pristine Co3O4. The Co3O4/Bi5O7I can remove 86.67% tetracycline in 90 min and shows enhanced photocatalytic activities, which are about 6 times higher than those of the pristine Co3O4. The possible mechanisms of photocatalytic degradation were analyzed by trapping experiments, electron paramagnetic resonance, photocurrent, and electrochemical impedance measurements. The direct Z-scheme structure of Co3O4/Bi5O7I composites facilitated the charge separation and transportation of the photogenerated electrons and holes.

Simultaneous Determination of Chemical Oxygen Demand, Total Nitrogen, Ammonia, and Phosphate in Surface Water Based on a Multielectrode System.

A technique for monitoring chemical oxygen demand (COD), total nitrogen (TN), ammonia (N-NH4), and phosphate (P-PO4) in surface water with a targeted signal multielectrode system (Cu, Ir, Rh, Co(OH)2, and Zr(OH)4 electrodes) is proposed for the first time. Each water quality index is specifically detected by at least two electrodes with distinct selectivity sensing mechanisms. Cyclic voltammetry and electrochemical impedance measurements are employed for multidimensional signal acquisition, complemented by normalization and Least Absolute Shrinkage and Selection Operator (LASSO) for principal feature extraction and dimension reduction. Multiple linear regression (MLR), partial least-squares (PLS), and eXtreme Gradient Boosting (XGBoost) were employed to evaluate the established prediction model. The precisions of the multielectrode system are ±10%/±5 ppm of COD, ±10%/±0.2 ppm of TN, ±5%/±0.1 ppm of N-NH4, and ±5%/±0.01 ppm of P-PO4. The analysis time of the multielectrode system is reduced from hours to minutes compared with traditional analysis, without any sample pretreatment, facilitating continuous online monitoring in the field. The developed multielectrode system offers a feasible strategy for online in situ monitoring of surface water quality.

Effects of substrate materials and electrodeposition parameters on hydrogen evolution reaction of Ni–Cu–Fe coatings

In this study, the effects of substrate materials and electrodeposition parameters on the hydrogen evolution reaction (HER) of Ni–Cu–Fe coatings were studied. For this purpose, different materials, including carbon steel (CS), stainless steel 304 (SS), and pure commercial graphite (G) were used as substrates, while the coating process was done in both modes of constant current density (CC) and variable current density, the latter to produce a functionally-graded (FG) coating. Microstructural investigations were done by using scanning electron microscopy, while the HER behavior was analyzed by electrochemical tests, including cyclic voltammetry (CV), linear scanning voltammetry (LSV), and electrochemical impedance (EIS) measurements. The morphology of the produced Ni–Cu–Fe coatings was completely affected by the coating parameters in the deposition bath and the type of substrates. In samples with micro/nano-cone morphology, deposited at a constant current density of 2.5 A/dm2, better HER behavior was obtained due to the highly effective surface and easier separation of hydrogen bubbles. Besides, the best electrocatalytic activity and the lowest overpotential (110 mV at 10 mA/cm2 in CC mode) were related to the samples coated on G. The proper selection of the substrate material plays an important role in improving the electrocatalytic behavior of composite coatings.

Facile fabrication of a flower-like superhydrophobic copper surface with superior corrosion resistance

Abstract A superhydrophobic copper coating was prepared by combining ionic liquid copper electrodeposition and a brief stearic acid modification process. After modification, the copper stearic acid was well formed and flower-like clusters were present on the surface of the superhydrophobic coating. Finally, the surface of the sample exhibits a good superhydrophobic performance with a contact angle of 158° and obvious self-cleaning behavior. The results of potentiodynamic polarization and electrochemical impedance measurements revealed that the presence of a superhydrophobic surface could improve the anti-corrosion property of the samples.

Quantifying intergranular corrosion susceptibility in AA2098‐T351 weldments through friction stir welding

AbstractIn this study, the intergranular corrosion (IGC) susceptibility of AA2098‐T351 welds, fabricated through friction stir welding (FSW), was systematically evaluated. The evaluation employed American Society for Testing and Materials (ASTM) G110‐92 practice and electrochemical impedance measurements, with comparative analyses against unwelded alloys (BS). The key findings depicted that FSW‐induced microstructure changes significantly influenced IGC susceptibility across different zones. Zones affected by FSW presented distinct susceptibilities compared with the base metal (BM). The ASTM G110‐92 test effectively differentiated the heat‐affected zone (HAZ) into segments with changing corrosion resistances based on welding temperature gradients. Cross‐sectional analyses using scanning electron microscopy (SEM) techniques correlated corrosion characteristics with microstructural features identified by transmission electron microscopy (TEM). Overall, FSW‐induced microstructural alterations emerged as a predominant factor influencing the varying susceptibilities of different zones to IGC, and electrochemical impedance measurements (EIS) validated the findings from ASTM G110‐92 practice.

Distinct electrochemical behavior of P3 and P2 polytypes of Mn/Ni-based Na-ion battery cathode

A layered sodium-ion battery cathode Na34Mn1116Ni316Al216O2 (NMNA) prepared in P3 and P2 polytype structures by varying the calcination temperature is systematically investigated for its structural and electrochemical behavior. P3-phase prepared at 650 °C delivered a higher initial capacity of 164 mAh/g (∼148 mAh/g for P2-phase calcined at 850 °C) at 0.1C. In contrast, the P2-phase sample exhibited better rate performance (87 mAh/g vs. 70 mAh/g for P3-phase at 4C) and capacity retention of ∼47 % after 200 cycles (only ∼26 % for P2-phase). Electrochemical impedance measurements before and after cycling confirmed that the increase in charge transfer resistance is responsible for the poor rate performance of the P3 phase.

Niobium Oxides: The key role of hydroxylated surface on photocatalytic driven C–C reductive coupling of acetophenone

Aromatic diols play a pivotal role in various industries as crucial components of bulk feedstock and fine chemicals, particularly in pharmaceutical production. However, the complexity of the chemical reactions involved in their synthesis often poses challenges for achieving high yields and purity. This study introduces an alternative approach for the synthesis of 2,3-diphenylbutane-2,3-diol (DPB) and 2-phenylbutane-2,3-diol (PB) using niobium oxides as photocatalysts for C–C reductive coupling with acetophenone as the substrate. Niobium oxides were synthesized from commercially available niobic acid (HY-340) via calcination at various temperatures. The characterization data revealed the critical impact of thermal treatment on the acid-hydroxylated surface groups of niobic acid, which strongly influenced the photocatalytic performance. Therefore, niobic acid emerged as the most active photocatalyst, achieving yields of 32.0 % and 35.1 % for PB and DPB, respectively, after 2 h of UV irradiation. Control experiments were conducted in conjunction with electron paramagnetic resonance and electrochemical impedance measurements to elucidate the mechanistic pathways governing the formation of DPB and PB, and to shed light on the significant role played by the surface structure of niobic acid in influencing the photocatalytic performance. This study not only provides valuable insights into the synthesis of aromatic diols but also emphasizes the significance of tailoring the surface properties of niobium oxide catalysts to enhance reactivity in photochemical processes.

Nitrogen-Doped Carbon Nanothin Film as a Buffer Layer between Anodic Graphite and Solid Electrolyte Interphase for Lithium-Ion Batteries.

Lithium-ion batteries are essential batteries for electric vehicle drive systems. Such batteries must provide stable performance over a long period of time. Therefore, the degradation or aging of the battery capacity must be improved. In the case of the current graphite anodes, graphite coated with an amorphous layer is used. It is known that the amorphous layer can reduce the irreversible capacity loss caused by the solid electrolyte interphase (SEI) layer. The amorphous carbon layers reduce the initial capacity due to higher electrical resistance. In this study, we aim to develop a buffer layer using nitrogen-containing graphene that would prevent the increase in electrical resistance while maintaining the amorphous structure. Coatings with different film thicknesses were prepared by using the solution plasma method. The thinnest sample was oven sintered to optimize the structure, especially the surface and interface of the layer. The battery capacity from charge-discharge experiments and the resistance change of each part from electrochemical impedance measurements were evaluated. The results showed that the coating layer increased the electrical resistance of the graphite anode. On the other hand, the resistance of the SEI layer was reduced by the coating layer. It can be predicted that the addition of the coating layer will increase the total charge transfer resistance (R ct) of the cell but will also improve the period average capacity in the long run. To be used as a practical material, the film thickness would need to be further reduced, and the balance between the loss of charge transfer resistance and the gain of SEI layer resistance would need to be further optimized.

Effect of normalizing treatments on microstructure and electrochemical corrosion properties of U75V-welded joints in an acidic environment

Corrosion poses a significant threat to the structural integrity of steel rails, especially in an acidic environment. In this study, we evaluate the corrosion properties of U75V-welded joints using potentiodynamic polarization curves, electrochemical impedance measurements, and corrosion morphology studies under simulated acidic conditions. Compared to non-normalized joints, the normalized joints exhibit a higher self-corrosion current (4.65 × 10−5 A/cm2) and a more negative self-corrosion potential (−0.56919 mV). The smaller and more uniform grain size obtained after normalizing provides multiple active sites on the surface for polarization reactions. Furthermore, owing to significant erosion caused on the rail surface by the acidic solutions, normalizing treatment enhances the passivation effects on the surface, resulting in increased corrosion resistance (221.96 Ω cm2). Our findings provide insights into the impact of normalizing treatments on the corrosion mechanism of U75V rail joints under acidic conditions.

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

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

Nanoporous Au Behavior in Methyl Orange Solutions.

Nanoporous (NP) gold, the most extensively studied and efficient NP metal, possesses exceptional properties that make it highly attractive for advanced technological applications. Notably, its remarkable catalytic properties in various significant reactions hold enormous potential. However, the exploration of its catalytic activity in the degradation of water pollutants remains limited. Nevertheless, previous research has reported the catalytic activity of NP Au in the degradation of methyl orange (MO), a toxic azo dye commonly found in water. This study aims to investigate the behavior of nanoporous gold in MO solutions using UV-Vis absorption spectroscopy and high-performance liquid chromatography. The NP Au was prepared by chemical removal of silver atoms of an AuAg precursor alloy prepared by ball milling. Immersion tests were conducted on both pellets and powders of NP Au, followed by examination of the residual solutions. Additionally, X-ray photoelectron spectroscopy and electrochemical impedance measurements were employed to analyze NP Au after the tests. The findings reveal that the predominant and faster process involves the partially reversible adsorption of MO onto NP Au, while the catalytic degradation of the dye plays a secondary and slower role in this system.

Influence of Solid Fraction on Particle Size during Wet-Chemical Synthesis of β-Li3PS4 in Tetrahydrofuran

For all-solid-state batteries, the particle size distribution of the solid electrolyte is a critical factor. Small particles are preferred to obtain a high active mass loading of cathode active material and a small porosity in composite cathodes. In this work, the influence of the solid fraction in the wet-chemical synthesis of β-Li3PS4 in tetrahydrofuran (THF) is investigated. The solid fraction is varied between 50 and 200 mg/mL, and the obtained samples are evaluated using X-ray diffraction, SEM and electrochemical impedance measurements. The sizes of the resulting particles show a significant dependency on the solid fraction, while a good ionic conductivity is maintained. For the highest concentration, the particle sizes do not exceed 10 µm, but for the lowest concentration, particles up to ~73 µm can be found. The ionic conductivities at room temperature are determined to be 0.63 ± 0.01 × 10−4 S/cm and 0.78 ± 0.01 × 10−4 S/cm for the highest and lowest concentrations, respectively. These findings lead to an improvement towards the production of tailored sulfide solid electrolytes.

Accurate ion type and concentration detection using two bare electrodes by machine learning of non-faradaic electrochemical impedance measurements of an automated fluidic system

Detecting ion types and their concentrations in multi-ion aqueous solutions poses a complex challenge with significant implications for sensing applications. This paper introduces an automated fluidic system using two bare electrodes to measure electrochemical impedance spectroscopy (EIS) data and evaluates deep neural network (DNN) for ion type and concentration detection. Additionally, a data-augmentation model is proposed for non-faradaic voltage sweep EIS data, intended for neural network training. To validate the effectiveness of our approach, prepared solutions featuring varying concentrations of LiCl, NaCl, and KCl are experimented. Impedance (Z) vs DC bias voltage (V) data, i.e., ZV-EIS are measured from −400 mV to + 400 mV at 9 different frequencies up to ∼ 200 kHz, for 148 automatically prepared solutions, having total salt concentrations up to 200 mM. DNN models are trained with augmented samples and successfully identified individual ions in test set solutions and their concentrations with 4.51 mM average deviation. The study delves into the nuanced impacts of factors such as sampling voltage window, and measurement frequency on the performance of the machine learning models, 8 mV and 20 Hz giving the most significant results.

Comparison of Approaches for Assessing Linearity of Impedance Measurements

Electrochemical impedance spectroscopy experiments are inherently nonlinear for systems affected by faradaic reactions. The methods used to determine whether an experiment is sufficiently linear include observation of current as a function of potential, known as Lissajous plots, measurement of total harmonic distortion, and post-experiment assessment of consistency with the Kramers–Kronig relations. An experimental approach is employed to compare sensitivity of these methods to determination of nonlinear response in electrochemical impedance measurements. The Lissajous figures showed linear behavior for a total harmonic distortion equivalent to 1 percent of the fundamental; whereas, the measurement model analysis revealed nonlinear behavior only for larger perturbation amplitudes.

Transfer of Sodium Ion across Interface between Na+-Selective Electrode Membrane and Aqueous Electrolyte Solution: Can We Use Nernst Equation If Current Flows through Electrode?

Electrochemical impedance and chronopotentiometric measurements with Na+-selective solvent polymeric (PVC) membranes containing a neutral ionophore and a cation exchanger revealed low-frequency resistance, which is ascribed to Na+ ion transfer across the interface between the membrane and aqueous solution. The attribution is based on the observed regular dependence of this resistance on the concentration of Na+ in solutions. The respective values of the exchange current densities were found to be significantly larger than the currents flowing through ion-selective electrodes (ISEs) during an analysis in non-zero-current mode. This fact suggests that the interfacial electrochemical equilibrium is not violated by the current flow and implies that the Nernst equation can be applied to interpret the data obtained in non-zero-current mode, e.g., constant potential coulometry.

Electrochemical Doping Effect on the Conductivity of Melanin-Inspired Materials.

Eumelanin is a natural pigment that can be particularly valuable for sustainable bioelectronic devices due to its inherent biocompatibility and hydration-dependent conductivity. However, the low conductivity of eumelanin limits its technological development. In this research, electrochemical doping was proposed as an alternative route to increase the electronic conductivity of synthetic eumelanin derivatives. Thin films of sulfonated eumelanin were deposited on platinum interdigitated electrodes and electrochemically treated by using cyclic voltammetry and chronoamperometry treatments. X-ray photoelectron spectroscopy analysis confirmed ion doping in sulfonated melanin. Current-voltage, current-time, and electrochemical impedance measurements were used to investigate the effect of different aqueous electrolytes (including KCl and LiClO4) treatments on the charge transport of sulfonated eumelanin. We show that the conductivity depends on the type and size of the anion used and can reach 10-3 S·cm-1. Additionally, depending on the electrolyte, there is a change in charge transport from mixed ionic/electronic to a predominantly electronic-only conduction. Our results show that the chemical nature of the ion plays an important role in the electrochemical doping and, consequently, in the charge transport of eumelanin. These insights serve as inspiration to explore the use of alternative electrolytes with different compositions further and develop eumelanin-based devices with tunable conductivities.

Corrosion of 316L stainless steel produced by laser powder bed fusion and powder metallurgy in pressurized water reactor primary coolant

Corrosion mechanism of 316 L stainless steel produced by laser powder bed fusion-hot isostatic pressing (LPBF-HIP) and powder metallurgy-hot isostatic pressing (PM-HIP) is studied with in-situ electrochemical impedance measurements coupled to detailed oxide film characterization. Quantitative analysis of impedance spectra using the Mixed-Conduction Model and estimation of local kinetic and transport parameters by interpretation of in-depth elemental composition profiles indicated lower corrosion and oxidation rates of LPBF-HIP and PM-HIP materials in comparison to conventional wrought 316 L. This owes to a higher fraction of low-angle grain boundaries, smaller grain size, the presence of nano-sized oxide particles and elevated Cr and Ni contents.

Unraveling the structure-property relationship of pyrimidine-derivatives as CO2 corrosion inhibitors: Experimental and periodic DFT investigations

CO2-containing environments commonly cause corrosion of carbon steel (CS) pipelines used in the oil and gas industry. In this work, the inhibition of corrosion by three derivatives of pyrimidine, namely 2-mercaptopyrimidine (MPY), 4-hydroxy-2-mercapto-6-methylpyrimidine (HMMP), and 4,5-Diamino-2,6-dimercaptopyrimidine (DDMP) for C1018 CS in CO2 saturated 3.5% NaCl brine was investigated. The corrosion rates and inhibition efficiency were investigated at 25 and 70 °C using open circuit potential, linear polarization resistance, potentiodynamic polarization and electrochemical impedance measurements. The post-immersion surface characterization of the exposed C1018 CS with and without the three molecules was carried out using SEM and 3D surface optical profilometer. Theoretical computation using DFT was further utilized to examine the role of the molecular structures and the mechanism of inhibition of the three molecules on steel surface at the atomic level. The experimental results indicate the following order of inhibition efficiency: MPY > DDMP > HMMP. Our experimental work proved that MPY molecule (the smaller one with the least number of heteroatoms) as the most efficient corrosion inhibitor. Surface characterization analysis confirmed the order of inhibition efficiency. The theoretical results revealed that the stability of molecules adsorbed on Fe (110) surface in the parallel orientation and on FeCO3 (104) is identical on both surfaces, which is completely consistent with the experiment. Our study provides a feasible strategy for developing new corrosion inhibitors by understanding how similar organic inhibitors work.