Electrochemical Impedance Spectroscopy Investigations Research Articles

Hydrogen storage performance of the multi-principal-component CoFeMnTiVZr alloy in electrochemical and gas-solid reactions.

The single-phase multi-principal-component CoFeMnTiVZr alloy was obtained by rapid solidification and examined by a combination of electrochemical methods and gas–solid reactions. X-ray diffraction and high-resolution transmission electron microscopy analyses reveal a hexagonal Laves-phase structure (type C14). Cyclic voltammetry and electrochemical impedance spectroscopy investigations in the hydrogen absorption/desorption region give insight into the absorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The thickness of the hydrogen absorption layer obtained by the electrochemical reaction is estimated by high-resolution transmission electron microscopy. The electrochemical hydrogen storage capacity for a given applied voltage is calculated from a series of chronoamperometry and cyclic voltammetry measurements. The selected alloy exhibits good stability for reversible hydrogen absorption and demonstrates a maximum hydrogen capacity of ∼1.9 wt% at room temperature. The amount of hydrogen absorbed in the gas–solid reaction reaches 1.7 wt% at 298 K and 5 MPa, evidencing a good correlation with the electrochemical results.

Low temperature synthesis of MnO2 nanostructures for supercapacitor application

Herein, we are reporting a facile and novel TEA-ethoxylate assisted low temperature hydrothermal route for synthesis of stable nanostructured MnO2 and their application as an electrode material in supercapacitor. The synthesis was accomplished at two different reaction temperatures viz. 60 °C and 80 °C. The synthesized samples were characterized by various physicochemical characterization techniques viz. XRD, FESEM, FTIR and BET-BJH surface area analysis etc. The morphological study of the as-synthesized MnO2 samples revealed the mixed morphology consisting of nanorod and nanocrystals. The electrochemical studies revealed that the sample prepared at 80 °C exhibits superior electrochemical behavior in 1 mol L−1 Na2SO4 liquid electrolyte solution and demonstrated high specific capacitance of ~348.2 Fg−1 at a current density of 0.1 mAcm−2 and energy density of 43.3 WhKg−1. Further, this electrode showed high rate capability of 89% after 2000 cycles. The electrochemical impedance spectroscopic investigations revealed the low equivalent series resistance for MnO2 electrode. This work represents the promising performance of the nanostructured MnO2 electrode for high energy density supercapacitor application.

Over-oxidized carbon paste electrode modified with pretreated carbon nanofiber for the simultaneous detection of epinephrine and uric acid in the presence of ascorbic acid

A new procedure for sensitizing of carbon paste electrode modified with carbon nanofiber by applying a special potential in differential pulse voltammetry is introduced. It is found out that the selection of 1.4 V as conditioning potential to a period of time can boost the electrochemical peaks of epinephrine and uric acid. In addition, the special potential leads to separated oxidation peaks of epinephrine and uric acid from ascorbic acid (potentially interfering species). The electrochemical impedance spectroscopic investigations confirm the good conductivity of the modified electrode. Surface characterization studies were done using scanning electron microscopy. Under optimum conditions, the oxidation peaks of epinephrine and uric acid were linear in the range of 0.1–150 μM and 0.08–250 μM, respectively, when they determined individually. The linear dynamic range from 0.2 to 30.0 μM was obtained for the simultaneous determination of epinephrine and uric acid in the presence of ascorbic acid. Wide linear range, amplified and sharp peaks, reproducibility and stability allow this procedure to analyze epinephrine and uric acid in the presence of ascorbic acid. The proposed electrode was successfully applied for the determination of epinephrine and uric acid in epinephrine hydrochloride injection, human urine samples and human blood serum.

Electrocatalysis enhancement of α, β-PbO2 nanocrystals induced via rare earth Er(III) doping strategy: Principle, degradation application and electrocatalytic mechanism

Novel Ti/Sb2O3–SnO2/Er–PbO2 anodes were fabricated based on doping Er ions into the PbO2 crystal and enhanced electrocatalytic degradation efficiency for organic pollutants was achieved successfully. The doping principle, possible degradation pathway of methylene blue and electrocatalytic mechanism have been discussed in depth. Based on the comprehensive analysis of crystal parameters by X-ray diffraction (XRD) results and typical formulas, the doping principle was confirmed to be the partial substitution of Pb ions by Er ions in PbO2 nanocrystal and might form point defects. Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) investigation indicated that the Ti/Sb2O3–SnO2/Er–PbO2 anodes possessed higher oxygen overpotential and better conductivity than undoped electrodes. The optimum conditions for the degradation of methylene blue were obtained via studying the effects of different parameters, such as electrolyte concentration (0.01–0.4 M Na2SO4), current density (20–60 mA cm−2), initial methylene blue concentration (10–70 mg L−1) and initial pH (3–11). At the optimum conditions, the total organic carbon (TOC), the decolorization rate constant (kdec) and the energy consumption (EC) reached up to 65.34%, 0.036 min−1 and 0.08 (kWh(gTOC))−1, respectively. Moreover, the electrocatalytic degradation mechanism of the Ti/Sb2O3–SnO2/Er–PbO2 anodes to methylene blue was proposed to be that, the presence of point defects induced an increase of electron transport tunnels, and promoted the production of more hydroxyl radicals (OH) and SO4-. The possible electrocatalytic mineralization pathway of methylene blue at Ti/Sb2O3–SnO2/Er–PbO2 anodes was also speculated by UV–visible absorption spectroscopy, gas chromatography combined with mass spectrometry (GC-MS) and liquid chromatography combined with mass spectrometer (LC-MS). This work will provide significant references for exploring the mechanism between doped electrodes materials and electrocatalytic degradation performance.

Electrochemical investigation of graphene on the corrosion of scratched polyurea based organic coating

It is still a contentious issue whether graphene is added as filler to the organic coating is a metal corrosion inhibitor or a promoter. To address this issue, this study provides a deep understanding of the effects of highly conductive graphene on corrosion promotion of polyurea-based organic coating via scanning vibrating electrode technique (SVET) and electrochemical impedance spectroscopy (EIS) investigations. The investigation shows that, with the enhancement of graphene loading (0.05 wt%∼1 wt%), corrosive promotion effects near the scratch position for different samples are evidently observed and quantitatively detected, specifically, the total anodic currents increased from 0.83 to 19.75 μA. And the final results have revealed that a small proportion of graphene (∼1.05 × 10-10 S m−1) are likely to induce accelerated local galvanic corrosion in the local area of damaged coating. This study undoubted helps to develop polyurea based hybrid coatings efficiently for anticorrosive applications, and call for attention to the damage to the protected metal caused by the high conductivity of the coating matrix.

Enhancing catalytic activity of rhodium towards methanol electro-oxidation in both acidic and alkaline media by alloying with iron

The methanol electrooxidation catalysts in the form of Rh and FeRh thin films were prepared by magnetron sputtering deposition. To activate the FeRh catalyst, the as-prepared FeRh films were cycled in 0.1 M HClO4 electrolyte in potential window from −0.25 V to 0.8 V (vs. Ag/AgCl). The dissolution of Fe atoms during the cycling leads to the formation of Rh-skeleton surface. Obtained FeRh catalysts exhibit significantly enhanced activity to methanol electrooxidation in both acidic and alkaline environments comparing to pure Rh catalyst. The optimal concentration of Fe is found to be 50%. Electrochemical impedance spectroscopy investigations show the higher rate of methanol dehydrogenation as well as better tolerance to CO intermediates poisoning of the FeRh catalysts. This study demonstrates that Rh-based catalysts can be considered as alternative to Pt-based catalysts.

The synergistic supercapacitive performance of Mo-MOF/PANI and its electrochemical impedance spectroscopy investigation

The molybdenum-based metal organic framework (Mo-MOF) and polyaniline (PANI) composite is successfully prepared via in situ polymerization of aniline monomers. BET analysis reveals that the obtained Mo-MOF/PANI composite possesses larger specific surface area which is beneficial for its electrochemical performance. The charge-transfer resistance of the composite is greatly lower than that of the individual material. Meanwhile, the superior cycling stability and rate capability based on its favorable interface kinetics with faster charge transfer speed are also observed. The electrochemical kinetics investigated via electrochemical impedance spectroscopy reveals that Mo-MOF/PANI exhibits fast ion transformation rate.

EIS investigation and patina characterization of weathering steel exposed to each of the four seasons in the São Paulo metropolitan area

Weathering steel (WS) is a low alloy steel particularly suitable for outdoor exposures. When exposed to wet and dry cycles, they develop a protective patina layer with complex composition, effectively reducing the corrosion rate. However, several years are necessary to completely develop this layer. Aiming to investigate the seasonal dependence on the climatic parameters and concentration of pollutants in the atmosphere in the patina development at early stages, the present study investigates the corrosion behavior of patina layers formed on WS exposed to the atmosphere of the São Paulo metropolitan area during a period corresponding to each of the four seasons, employing open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and electric equivalent circuit (EEC) fitting. SEM, Raman spectroscopy and thicknesses evaluation were used to characterize the patinas. The results showed that, while the patina compositions were independent of the exposure period, their thicknesses and corrosion resistances were extremely dependent on this variable. Excessive rain and wetting periods, as well as the presence of pollutants, proved to be deleterious, leading to the development of non-protective patinas. Based on the EEC fitting procedure, a model was proposed to explain the EIS responses of the patina layers based on the porous electrode theory initially developed by de Levie.

Preparation and characterization studies of La doped CuS nanospheres by microwave irradiation for high performance supercapacitors

Lanthanum (Rare earth metal) doped CuS (La@CuS) at different compositions (0%, 1%, 3% and 5% of La) are synthesized by encapsulation of sodium alginate biopolymer using microwave irradiation method. The prepared various compositions of La@CuS are examined by structural characterizations, particle size and identifications of elements from XRD, TEM and EDX spectrum. The surface morphological studies are conformed by SEM and TEM images. Optical properties and characteristics peak are confirmed with UV, FTIR and Raman spectroscopic tools. In addition to that the electrochemical performances are studied using Cyclic Voltammetry (CV), Galvanostatic charge and discharge (GCD) and electrochemical impedance spectroscopy (EIS) investigations. The specific capacitance is found to be 1329 F/g for 5% of La doped CuS nano spheres.

Localised electrochemical impedance spectroscopy investigation of polymer electrolyte membrane fuel cells using Print circuit board based interference-free system

Polymer electrolyte membrane fuel cells are promising power sources for vehicle and other portable applications due to their high energy efficiency and zero pollution emission during operation. To improve the performance and reliability of polymer electrolyte membrane fuel cells, effective and accurate diagnostic tools are urgently needed for polymer electrolyte membrane fuel cells practical applications. Different from the previous diagnostic methods that may damage the fuel cell structure, a novel interference-free diagnostic system based on the printed circuit board is proposed in this study. Fuel cell localised electrochemical impedance spectroscopy at different current density is observed. It is found that the activation impedance near inlet decreases sharply when current density increase. In addition, it is also found the flooding problem and the mass transport problem can occur at a medium current density due to the non-uniform behaviour of the polymer electrolyte membrane fuel cells. The proposed diagnostic system is demonstrated to be an effective tool to improve efficiency and robust of polymer electrolyte membrane fuel cells.

Direct Z-scheme CaTiO3@BiOBr composite photocatalysts with enhanced photodegradation of dyes.

To efficiently separate photoexcited electron/hole pairs is one of the key points for achieving excellent photocatalysts with high photocatalytic performances. To achieve this aim, here we have assembled CaTiO3 (CTO) nanoparticles onto BiOBr microplates, thus constructing novel Z-scheme CTO@BiOBr heterojunction composite photocatalysts. Observation by scanning/transmission electron microscopy confirms the good decoration of CTO nanoparticles (15-50nm) on the surface of BiOBr microplates (diameter 0.7-2.2μm, thickness 70-110nm). Simulated sunlight was used as the light source, and rhodamine B (RhB) in aqueous solution was used as the model pollutant to assess the photodegradation activity of the samples. It is demonstrated that the CTO@BiOBr composites with an appropriate CTO content exhibit much enhanced photodegradation performances. In particular, the 10%CTO@BiOBr composite with a CTO mass fraction of 10%, which photocatalyzes 99.9% degradation of RhB at 30min of photocatalysis, has a photocatalytic activity which is about 1.8 and 23.6 times larger than that of bare BiOBr microplates and CTO nanoparticles, respectively. This can be explained as the result of the Z-scheme electron transfer and efficient separation of photoexcited electron/hole pairs, as evidenced by photoluminescence, photocurrent response, and electrochemical impedance spectroscopy investigations.

New hybrid phosphite (CH3OH)Cd(H2PO3)2: Synthesis, characterization and application of nanocomposite

(CH3OH)Cd(H2PO3)2 (CdP) has been synthesized in solution, it was characterized by single crystal X-ray diffraction and Fourier-transform infrared spectroscopy (FT-IR). The impact of CdP nanoparticles on the protective performance of polyurethane (PU) coatings was investigated. The anti-corrosion performance of new CdP/PU nanocomposite coatings was characterized by electrochemical impedance spectroscopy (EIS), cathodic disbanding and pull-off adhesion investigations. The results indicated that the anti-corrosion property and the cathodic disbanding resistance of the PU coatings were significantly improved by adding CdP nanoparticles.

(Invited) Process Control of Advanced Cobalt Interconnect Plating Bath

Cobalt made an inevitable move into more and more applications as device features shrink. It has largely been replacing tungsten in prior forays: for encapsulating and for high-aspect-ratio fill. Cobalt now has a new target in its sights: copper interconnect [1]. Copper replaced aluminum about 20 years ago and had been successfully utilized in numerous semiconductor manufacturing nodes. However, when the IC industry moved beyond the 10 nm node, copper interconnects became more compact, causing an increase in the resistance-capacitance delay. One way to solve the problem is to utilize a cobalt metallization alternative that provides resistance benefits over conventional technology without compromising reliability and yield [2]. In this electroplating process, a super-filling relies on depletion of protons inside feature, leading to increased current efficiency for Cobalt. Depletion of protons in this case leads to reduction of suppression efficiency and further enhancement of cobalt deposition as compared to field [3, 4]. These publications agree that a successful super-filling requires tight pH control. This presentation reveals results of advanced method that allow to reach 0.005 pH repeatability required for electroplating process. While this cobalt plating process is maturing, tighter process control is required to provide more accurate and precise data as well as faster analysis data generation. Previously developed analytical methods [5, 6] had been refined and improved to address challenges of the modern industrial cobalt plating processes. New, efficient analytical techniques were also developed. These methods can also report additional properties of a plating solution (conductivity and pH) critical for bath performance. Fig 1. shows the electrochemical responses of different proprietary organic additives used in commercial cobalt plating baths. Optimized electroanalytical and hydrodynamic parameters enable the determination of a wide range of concentrations of organic additives without interference from other bath components, as well as from bath pH and temperature. Analysis of organic additives can be performed with relatively simple fluidics that include a single mini electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several or single injection of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations. One of the newly developed methods is non-reagent spectroscopic analysis of boric acid. This method can also be combined with non-reagent analysis of cobalt providing very fast analysis of both components. Fig. 2 shows correlation of obtained and expected values for wide range of boric acid concentrations. This presentation will provide more detailed information related to the electrochemical behavior of organic additives and inorganic components. The results of Electrochemical Impedance Spectroscopy investigations and Raman spectroscopy will also be presented. The presentation will be concluded with a discussion of analytical results for all bath components during electroplating process.

Effect of pH values on structural, optical, electrical and electrochemical properties of spinel LiMn2O4 cathode materials

Abstract In the present work, we have synthesized the spinel LiMn2O4 cathode materials via a sol-gel method at 750 °C for 8 h under optimal conditions at different pH values (3, 6 and 9) and studied the effect of different pH values on the structural, optical, electrical and electrochemical properties. X-ray diffraction (XRD) analysis identified the synthesized materials as crystallized in the cubic spinel structure (Fd3m) with slight decrease in the lattice parameters. SEM exhibits the formation of a spongy and fragile network structure in the synthesized samples. An enhancement in the optical energy band (Eg) leads to the blue shift in the synthesized samples with reduced crystallite size. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) investigations show that the LiMn2O4 nanostructures synthesized at pH 9 exhibit the long-term cycle constancy and a superior electrochemical reproducibility as compared to those synthesized at pH values of 3 and 6. The results revealed that pH plays a significant role in tuning the structural, optical and electrochemical properties of the LiMn2O4 cathode material, which is considered a promising substitute of cathode materials for the novel lithium-ion battery applications.

Toward nanograined gadolinia doped ceria via two-step sintering at ultralow temperature and its electrical conductivity

Abstract Highly dense (>98%) and nanograined (∼60 nm) gadolinia doped ceria are obtained from ultrafine powders by adopting two-step sintering (TSS) procedure at an ultralow temperature of 750 °C with a dwell time of 20 h, which is the lowest sintering temperature for ceria family without sintering aids up to now. Electrochemical impedance spectroscopy investigations suggest that the electrical conductivities of densified electrolytes are closely related to sintering temperature and grain size, and GDC900-750 exhibits the highest total electrical conductivity of 3.640 S m−1 at 700 °C in air. Fitting calculation indicates partial grain-size dependence of oxygen vacancy association enthalpy and grain-size independence of oxygen ion migration enthalpy. Grain boundary maturity influences on grain boundary conductivity to some extent, and younger grain boundary endues the densified electrolytes with higher grain boundary conductivity.

Probing into the working mechanism of Mg versus Co in enhancing the electrochemical performance of P2-Type layered composite for sodium-ion batteries

As a cost-effective element, Mg has been applied as doped inactive atom to improve the electrochemical performance of sodium-ion cathode materials. Herein, we report Mg-substituted Na0.67Mn0.65Ni0.2Co0.15-xMgxO2 composites as high-performance cathode for sodium-ion batteries and investigate the underlying working mechanism using in situ investigation techniques to monitor the operando changes of electrodes. In situ X-ray diffraction investigation demonstrates P2-type structure is well preserved even charged to 4.3 V and the changes of lattice parameters and unit cell volume of Na0.67Mn0.65Ni0.2Mg0.15O2 are alleviated via Mg replacement. As a result, the capacity retention increases from 62% in Na0.67Mn0.65Ni0.2Co0.15O2 to 94% in Na0.67Mn0.65Ni0.2Mg0.15O2. Meanwhile, less CO2 evolution was detected in the coin cell with Na0.67Mn0.65Ni0.2Mg0.15O2 electrode than in that with Na0.67Mn0.65Ni0.2Co0.15O2 electrode in online differential electrochemical mass spectrometry test, suggesting a depressed side reaction between electrode and electrolyte after Mg completely replacing Co. In situ electrochemical impedance spectroscopy investigation further proves Mg is beneficial for the interfacial conductivity enhancement compared to Co, which provides evidence for enhanced high rate capabilities. These comprehensive results provide new viewpoints to explain the improved cycling and rate capabilities from the aspects of crystal structure evolution, coin cell gas evolution and electrolyte/electrode interface conductivity during charge/discharge process.

Novel chitosan-Nafion composite for fabrication of highly sensitive impedimetric and colorimetric As(III) aptasensor

In the present work, for the first time we takes the advantages of chitosan-Nafion (Chit-Naf) composite as a highly conductive surface platform and a novel CNT-based signal amplification strategy to develop a lable-free impedimetricaptamer-based sensor for highly sensitive detection of As(III). The electrochemical impedance spectroscopy (EIS) investigations surprisingly revealed that the glassy carbon electrode (GC) electrode modified with Chit-Naf composite had higher electron transfer kinetics compared the bare GC, GC/Naf and GC/Chit electrodes, which promises a great potential as an efficient platform in construction of biosensing assays. In this work, we employed a signal amplification strategy based on carbon nanotube-bovine serum albumin (CNT-BSA) hybrid system, by which sensitivity and detection limit of the aptasensor for the detection of As(III) were obtained to be 100.82 Ω nM−1 and a of 74 pM, respectively. This protocol provided one of the lowest limits of detection for As(III) on aptamer-based electrodes recently described in the literature. Moreover, the change of the optical absorptive properties of CNTs upon biorecognition interactions provides a way to detect the biorecognition process and thus allowed us to design an optical As(III) aptasensor using the UV–Vis spectroscopic method. The discrimination capability of the fabricated aptasensor for recognizing As(III) in the presence of other metal ions and a complex matrix of waste water samples was successfully investigated. This protocol provided a new method for sensitive detection of As(III) with considerable advantages in terms of reproducibility, selectivity, being mediator free and regenerability of the sensing interface.

Corrosion behavior and adhesion strength of PEO/Epoxy duplex coating applied on aluminum alloy

PurposeThis paper aims to increase protection behavior of epoxy coating on aluminum alloys with plasma electrolitic oxidation (PEO) process as pretreatment and to investigate the corrosion properties of duplex coating system on aluminum alloy.Design/methodology/approachThe study used micro structure study, electrochemical impedance spectroscopy (EIS) investigation, water uptake investigation and pull-off test.FindingsThis study was done to investigate the effect of urea as an additive, which alters the current density and time of process parameters in the protective performance of epoxy coating on the aluminum substrate. The protective behavior of double-layer coatings was examined using EIS in 3.5 per cent NaCl solution. In addition, the adhesion strength of double-layer coatings was evaluated using pull-off test, and the results demonstrated that the adhesion strength of sample with higher content of urea and current density is about two times that of sample without PEO preparation.Originality/valueThe protective properties and adhesion strength of epoxy coating can be increased with PEO pretreatment.

Electrochemical Behavior and Analysis of Organic Additives in Modern Lead Free Wafer Level Packaging Plating Baths

Replacement of tin-lead solder bumps by a suitable lead-free material for flip chip attachment has become an urgent necessity due to the impending ban on the use of lead in electronics. Alloys containing Sn and Ag as well as pure Sn are the most common for the replacement of Sn-Pb. The mechanical strength, wetting, and fatigue resistance of these alloys and pure Sn is comparable or surpass that of Sn-Pb”. Electroplating with lead-free alloys is the most desirable technique due to its low cost and usefulness in building small dimension bumps. However, the co-deposition of elements is complicated by the large difference in the electrode potentials of each element. Besides metal ions, these plating baths include organic additives, chelating agents, and acids. For appropriate plating bath performance, these components must be kept within specific concentration ranges. This is achieved through the use of dedicated chemical analyzers and dosers [1]. Most of these systems use multiple analytical methods that typically include electrochemical techniques. The introduction of new electroplating processes requires the development of new analytical methods. Before a new analytical electrochemical method is developed, the interactions between bath components should be investigated and understood. For this purpose, we utilized an electrochemical cell with three electrodes connected to a potentiostat/galvanostat. We studied the responses of organic components under varying electrochemical and hydrodynamic conditions as well as at different concentrations of bath components. Fig. 1 shows the electrochemical responses of organic additives used in commercial lead-free plating baths [2]. All tests were performed with the working and counter platinum electrodes and a low maintenance Ag/AgCl double junction reference electrode. Optimized electrochemical analysis parameters enable the determination of a wide range of concentrations of organic plating additives without interference from other bath components. Analysis of organic additives can be performed with relatively simple fluidics that include a single electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several injections of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations. This presentation will provide more information related to the electrochemical behavior of organic additives and inorganic components. Results of Electrochemical Impedance Spectroscopy investigations will also be presented. Results of electrochemical analyses will be correlated to data obtained with an HPLC analytical technique. The presentation will be concluded with a discussion of analytical results for each organic additive at different concentration levels.

Validating the early corrosion sensing functionality in poly (ether imide) coatings for enhanced protection of magnesium alloy AZ31

This work reports on the validation studies of early corrosion sensing poly ether imide (PEI) coatings with incorporated pH-sensing phenolphthalein loaded silica nano-sized capsules (SiNCs-PhPh) on AZ31 magnesium alloys. Immersion and drop tests validated the high sensing accuracy and PhPh color-signaling reproducibility of the coatings upon onset of corrosion. This behavior is correlated to the homogeneous dispersion of SiNC particle agglomerates confirmed by 3D Raman mapping and SEM analysis. Complementary differential video imaging technique (DVIT) assisted by electrochemical impedance spectroscopy (EIS) investigations provided clues for a good correlation between the kinetics of color signaling and the corrosion activity. Mechanistic insights into the pH-sensing/color-signaling functionality in PEI coatings are suggested.