Employing Electrochemical Impedance Spectroscopy Research Articles

Enhancing tetracycline degradation with biomass carbon quantum dot (CQDs)-modified magnetic heterojunction CeO2-Fe3O4 under visible light

This research investigates the synergistic enhancement of semiconductor catalysts through the incorporation of carbon quantum dots (CQDs) within CeO2-Fe3O4 Type-II heterojunction photocatalysts. Subsequent to the successful synthesis of these modified photocatalysts, a thorough assessment of their catalytic performance is conducted. Notably, the introduction of CQDs results in a 21% increase in pollutant degradation capacity compared to unmodified heterojunctions, with a remarkable removal efficiency of 96% for the target pollutant TC. Comprehensive analyses employing electrochemical impedance spectroscopy (EIS), UV–vis spectroscopy, and photocatalytic experiments provide substantial evidence for the efficacy of CQDs in enhancing light absorption properties within the CeO2-Fe3O4 heterojunction. This enhancement is attributed to a notable suppression of electron-hole pair recombination, facilitating the generation of reactive oxygen species (ROS) such as ·O2- and ·OH. This, in turn, the promotion of Ce4+/Ce3+ and Fe3+/Fe2+ cycles takes place, collectively enhancing the responsiveness of the photocatalyst to visible light. The photocatalysts demonstrate enduring catalytic and magnetic stability over five cycles, as indicated by the sustained high-performance retention. Detailed analysis using TOF-LC-MS has revealed two highly efficient degradation pathways for the for the target pollutant. The findings contribute valuable insights for advancing the performance of heterojunction photocatalysts.

Evolution of interfacial defects and energy losses during aging of organic photovoltaics

As the power conversion efficiencies of Organic Solar Cells (OSCs) approach 20 %, the stability of the device becomes an increasingly urgent issue. To enhance device stability, it is crucial to identify potential loss mechanisms. In this study, we investigated the trap-state-dependent degradation mechanism of OSCs by directly comparing devices with different hole transport layers (HTLs) that introduce distinct interfacial defect distributions. Employing electrochemical impedance spectroscopy (EIS), Fourier transform photocurrent spectroscopy (FTPS), electroluminescence quantum efficiency (EQEEL), and temperature-dependent J-V techniques, we unraveled the relationship between device degradation and interfacial trap states and energy loss in PM6:Y6 devices. A lower density of interfacial deep traps is evidently correlated with smaller non-radiative recombination losses during the aging of devices based on PEDOT:PSS. Conversely, a higher density of deep traps in aged devices with WS2 interlayers and HTL-free configurations is presumed to be responsible for a significant increase in non-radiative recombination losses. The escalating deep-trap-state density in aged devices is observed to elevate carrier recombination, consequently deteriorating device performance. Beyond the scope of the energy balance theory, an additional factor, probably attributed to the change in the work function of ITO, was found to contribute significantly to energy loss in aged cells, particularly in HTL-free devices. These results highlight the potential for improving device stability via interface engineering.

Controlling corrosion protection of mild steel in acidic environment via environmentally benign organic inhibitor

The current research employed electrochemical techniques to evaluate a green corrosion inhibitor Subphthalocyanine chloride (SubPc) to control the corrosion mitigation of mild steel in acidic environments. The corrosion rates and hydrogen evolution rates were measured by weight loss. The inhibitor was found to be highly effective with a corrosion-inhibiting efficiency up to 97.6% at a concentration of 150 ppm in 1 M HCl solution loaded with synthesized (SubPc) through variable concentrations. According to the obtained information from the polarization technique, the corrosion current density, icorr, decreases with increasing the concentration levels of (SubPcs) inhibitors in 1 M HCl medium. The inhibition mechanism of mild steel has been suggested as well as its excess surface charge was determined employing electrochemical impedance spectroscopy (EIS). The results suggest that the inhibitory functions by forming a protective barrier on the steel surface, hindering the corrosion process. The present study provides a new insight into developing eco-friendly and cost-effective corrosion inhibitor to protect mild steel from acidic corrosion.

Investigating the Change in the Microporous Structure of the Graphite Electrode during Formation

Till today, the graphite-based electrode is the most widely used negative electrode in commercially available lithium-ion batteries (LIBs).[1] While extended research has been conducted in the investigation of the graphite electrode’s properties, especially the formation of the solid-electrolyte interphase (SEI) within the first cycles of LIBs remains a field of ongoing research.[2] The SEI forms during the first cycle(s) on the anode surface at potentials below the stability window of the electrolyte components, due to the reductive decomposition of the respective solvents, additives, and conductive salts.[2,3] The initially formed SEI has an influence both on the long-term cycling stability of the cell, depending on how good the passivation, i.e., electronic insulation, of the graphite surface is,[4] and on the rate performance of the anode, depending on the thickness of the SEI, its chemical composition, and its lithium-ion conductivity, referred to as SEI resistance.[5] Additionally, with a thickness of 10-20 nm when employing additives such as vinylene carbonate (VC), the SEI takes up parts of the void volume of the pristine electrode and may change the pores and the electrolyte conduction pathways within the electrode (see Figure 1).[6] In this study, we investigated the change of the microporous structure of an artificial graphite (MAGE-5, Hitachi, Japan) with an LP572 electrolyte (1 M LiPF6 in EC:EMC 3:7 w:w with 2 wt% VC, Gotion, USA) during formation at 45 °C. The electrode’s microstructure is often connected to the macroscopic properties using the McMullin number N M in the form of:[7] N M = τ / ε = R Ion ·A · κ / d, (1)correlating the porosity ε, electrodes thickness d, ionic pore resistance R Ion, area of the electrode A, conductivity of the electrolyte κ, and the tortuosity τ (see Figure 1).Here, we analyzed graphite electrodes with varying initial porosities from 20 to 50 %, employing electrochemical impedance spectroscopy (EIS) in a MAGE//Li half-cell setup with a micro-reference electrode and a free-standing graphite electrode.[8,9] Measuring EIS at temperatures of -5 °C allowed the reliable determination of the ionic resistance before and after formation. Due to the formed SEI covering the graphite particles and partially filling the void of the porous electrode, we discovered an increase of the ionic pore resistance throughout the whole range of initial porosities.Next, we determined a porosity dependent increase in thickness of the electrodes from electrodes cycled at the same conditions in coin cells that were subsequently harvested from the cells and analyzed for thickness changes. Additionally, mercury intrusion porosimetry (MIP) was used to determine the porosity of formed graphite electrodes, revealing a decrease in porosity after formation for all samples. The combination of these findings - using Equation 1 as described above with a constant electrode area A and assuming a constant electrolyte conductivity κ - allowed us to evaluate the change in the tortuosity of the graphite electrodes, giving insights into the overall changes in the graphite anode properties due to SEI formation.

State-of-Charge Dependent Change in the Microporous Structure of Graphite Electrodes

Regarding the negative electrode, the most used electrode material in commercially available lithium-ion batteries (LIBs) up to the present day is graphite.1 Upon battery operation, an irreversible volume change in the microporous structure of the graphite electrode is detected. It is associated with the formation of the solid-electrolyte interphase (SEI) within the first cycles and an irreversible thickness increase of the electrode. Consequently, one observes a change in the electrode’s porosity after the initial formation cycles.2,3 Next to irreversible microstructure changes, one observes reversible changes in the microstructure associated with the intercalation of Li-ions into the host structure of the graphite particles upon charging the battery. The electrode particles expand during this process, increasing particle volume by ~13% when fully lithiated.4 In commercial LIBs, electrode materials, separators, and current collectors are tightly packed for a high volumetric energy density. This restricts the thickness expansion of the electrodes.5 Consequently, the graphite particles must expand into the internal pores of the electrodes, resulting in a decrease in the void volume of the porous network. Since the porous electrodes and the separator are filled with the electrolyte and the particle expansion of graphite is more significant than that of the active material in the positive electrode, one observes electrolyte motion in commercial LIBs during charge and discharge. It can be tracked by techniques requiring neutron beam facilities or expensive devices such as X-ray CT instruments.2,6 Recently, Aiken et al. developed a relatively simple apparatus to track the electrolyte motion by monitoring the changing moment of inertia of cylindrical cells during operation and simplifying the approach to study the discussed effect.In this study, we developed a method to track the reversible change of the microporous structure of an artificial graphite (MAGE-5, Hitachi, Japan) with an LP572 electrolyte (1 M LiPF6 in EC:EMC 7:3 w:w with 2 wt% VC, Gotion) during a charge and discharge cycle after formation employing electrochemical impedance spectroscopy (EIS) and operando dilatometry with both cell setups having a 1.5 bar cell compression Since the electrode’s microstructure is connected to the macroscopic properties using the MacMullin number of:NM=τ/ε=RIon·A·κ/dit correlates the porosity , electrodes thickness , ionic pore resistance , area of the electrode , conductivity of the electrolyte , and the tortuosity .8 Thus, we analyzed the change of the ionic pore resistance of graphite electrodes employing EIS in a MAGE//Li half-cell setup with a micro-reference electrode and a free-standing graphite electrode.Due to the particle expansion, we monitor an increase of the ionic pore resistance of up to 40% during charging, i.e., lithiation, of the graphite electrode.Next, we determined the SOC-dependent increase in thickness of the graphite electrode revealing a reversible thickness increase of 3%. Knowing the relation of porosity and tortuosity in a generalized Bruggeman form and using Equation 1 as described above with a constant electrode area and assuming a constant electrolyte conductivity , allowed us to extract the relative SOC-dependent decrease in porosity and void volume of the electrodes. At the end of the charge, both values decreased by approx. 10% and 9%, respectively, confirming the electrolyte repression from the graphite electrode.

Mixed hydride-electronic conductivity in Rb2CaH4 and Cs2CaH4

Hydride-ion conductors and mixed hydride-electronic conductors are promising materials for various applications, especially in (electro)chemical energy conversion and storage. Many of the hydride-ion conductors discovered to date are oxyhydrides with the K2NiF4-type structure. In this work, Cs2CaH4 and Rb2CaH4, which crystallize in the K2NiF4-type structure, were synthesized and electrochemically characterized. By employing electrochemical impedance spectroscopy (EIS) and single-step chronoamperometry measurements, it is found that both materials show mixed ionic-electronic conductivity at moderate (100–200 °C) temperatures. The overall conductivity of both materials is increased by the release of hydrogen at elevated temperatures, indicating an effect of hydride vacancy concentration on the conductivity. This suggests that the ionic conductivity is due to hydride-ion transport, which is further supported by Climbing Imaged Nudged Elastic Band (CINEB) calculations. Cs2CaH4 shows approximately equal ionic and electronic conductivity at 190 °C (total conductivity σ = 2.1 × 10−6 S cm−1), while Rb2CaH4 (σ = 8.8 × 10−7 S cm−1 at 190 °C) is primarily an ionic conductor. As mixed hydride-electronic conductors, both materials show promise in chemical conversion and energy conversion applications.

Study of the structure and electrical properties of graphene oxide (GO) and graphene oxide+nanocellulose (GO+NC)

Proton exchange membranes (PEMs) that function at elevated temperatures surpassing 100°C and exhibit exceptional mechanical, chemical, and thermochemical stability have garnered significant interest. This is primarily due to their practical utility in proton exchange membrane fuel cells (PEMFCs). In the present era, an extensive array of polymers and polymer-blended membranes have been scrutinized for their applicability in this domain. Each of these materials presents a set of advantages and disadvantages. However, the realm of PEMFCs is still in search of the perfect membrane endowed with distinct properties. Graphene oxide, a two-dimensional substance arising from the oxidation of graphite, has manifested itself as a promising candidate. Oxygen (O) functional groups are incorporated within the sp2 carbon (C) plane of the oxidized graphite, forming graphene oxide. This material can be synthesized by exfoliating graphite oxide, a three-dimensional carbon-based compound, into layered sheets using ultrasonic or mechanical agitation. The presence of multiple reactive oxygen functional groups renders graphene oxide suitable for a diverse array of applications, such as composite polymers, energy conversion materials, environmental safeguards, sensors, transistors, and optical components. This versatility is attributable to its outstanding electrical, mechanical, and thermal properties. Among the various methodologies for graphene oxide synthesis, the modified Hammer method stands out for its simplicity, cost-effectiveness, and high yield. This research delves into the structural analysis of graphene oxide obtained through the Hammer method, utilizing commercially available graphite. The study involves the creation of membranes based on carboxymethylcellulose (NC) that integrate dispersed graphene oxide (GO) sheets. These novel membranes, as well as pristine graphene oxide, were subjected to a comprehensive array of analytical techniques including XRD, XPS, Raman, FTIR, and SEM microscopy. Additionally, electrophysical characterizations were undertaken employing electrochemical impedance spectroscopy (EIS) measurements. The investigation uncovered that the introduction of NC into the graphene oxide matrix significantly enhances the electron conductivity of the composite membrane. Simultaneously, the presence of graphene oxide contributes to the mechanical robustness and thermomechanical stability of the membrane structure. The principal impetus behind this article lies in furnishing vital insights into the physical and structural attributes of graphene oxide membranes relevant to their deployment in hydrogen energy applications.

Investigating the Impact of Varying Quantities of TiO2 Nanoparticles on the Anti-Corrosive Characteristics of TiO2-Epoxy Nanocomposite Coatings

Prepared were pills coated with TiO2-epoxy nanocomposites, and their anti-corrosive properties were studied by examining the impact of varying amounts of TiO2 nanoparticles in the epoxy resin. The anti-corrosive characteristics of pills were investigated employing electrochemical impedance spectroscopy (EIS). Based on the EIS results, the sample containing 0.01 mg of TiO2 demonstrated the highest impedance value, indicating superior corrosion resistance and better anti-corrosion properties than the other samples. Also, this sample has the lowest corrosion current density among the all samples, with a value of 1.329E-07 mA/cm2, which shows that this sample has the best corrosion resistance and a slower rate of corrosion compared to the other samples.
  

Non-Enzymatic Electrochemical Sensors for Accurate and Accessible Uric Acid Detection

Gout arthritis, a painful condition characterized by the accumulation of uric acid (UA) crystals in the joints, necessitates the development of efficient and accessible diagnostic methods. In this study, we present the design and fabrication of non-enzymatic electrochemical sensors based on molecularly imprinted conducting polymer nanostructures for the selective detection and monitoring of UA. To overcome the limitations of current point-of-care (POC) diagnostics, we developed a disposable voltammetric sensor capable of selectively and accurately analyzing UA concentrations at room temperature and pH 7.4. The sensor utilizes a selective polythiophene layer, deposited on disposable screen-printed electrodes, for the reversible binding and recognition of UA. Extensive electrochemical measurements employing electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) demonstrate excellent UA sensing performance in the wider concentration range of 1–500 μM using a standard redox solution with 2.91 μA cm−2·μM−1 sensitivity, 354 nM detection limit, and substantial selectivity over common interferents. The sensor is capable of analyzing complex mixtures such as human saliva with 90.4% recovery of the spiked UA concentration. This highly sensitive and cost-efficient electrochemical sensor offers great promise for POC testing, disease monitoring, and predicting treatment outcomes related to gout arthritis.

Experimental and theoretical investigation of mild steel corrosion control in acidic solution by Ranunculus arvensis and Glycine max extracts as novel green inhibitors

In the present research, the ability of Ranunculus arvensis (RA) and Glycine max (GM) extracts as green corrosion inhibitors of mild steel (MS) in 1 M HCl was investigated. The inhibiting potential of RA and GM was analysed employing electrochemical impedance spectroscopy (EIS), polarization curves, potentiometry, and theoretical investigations. An enhancement in the inhibition efficiency (I.E) with increasing inhibitors concentrations indicated by EIS data and polarization curves. According to obtained results both extracts indicated inhibitory effect, with their effectiveness following the order of RA > GM. In addition, the interactions between the inhibitors on the MS surface were assessed using B3LYP/6-311g(d,p) theory level in liquid water phase. The interaction energies for three orientations of RA and GM depicted that inhibitors have located parallel to the alloy surface. The preferred complex orientation is one in which the maximum number of inhibitor donor atoms interacted with the alloy surface. Finally, experimental and theoretical results were in accordance which confirmed the inhibition effect of RA and GM extracts.

Analysis of charge transport properties of dye-sensitized solar cell (DSSC) with TiO2 working electrode by employing electrochemical impedance spectroscopy (EIS)

In this paper DSSCs of various electrode thicknesses (L = 3 ?m?12 ?m) are assembled using N719 dye, an iodide (I????)/triiodide (I???? ????) redoxliquid electrolyte and TiO2 (P-25) working electrode (WE). The theoretically modeled equations defining various bulk and interface impedances are incorporated with EIS spectrum analyzer software to fit the simulated EIS curves with experimentally measured EIS curves to evaluate the charger transfer and recombination properties of the assembled DSSCs. EIS fitting parameters investigated to study the impact of WE thickness on the charge transport properties of assembled DSSC. It is observed that the charger transfer resistance at TiO2/electrolyte interface (Rk) and series resistance (Rs) are reduced from 8 ?cm2 ? 4.05 ?cm2and 14.5 ?cm2?10.06 ?cm2 respectively which shows consistency with improvement in electron life time (?e) from 5.8 ms ?12.4 ms for increasing WE thickness, L = 3 ?m?12 ?m. The combined impact of significant reduction in Rk and Rs along with improved trend of ?e can be considered as major factors for efficient electron injection across Dye/TiO2 interface hence increases short circuit current (Isc) from 1.485 mA ? 2.365 mA and photovoltaic conversion efficiency (?) from 3.55 % ? 5.46 % for L = 3 ?m?12 ?m, respectively. Moreover, a remarkable increment in ? (~45%), ?e (~56.3%) and a noticeable reduction in Rk(~38.75 %), Rs (~23.8 %) are observed for WE variations (L = 3 ?m?6?m) and further shows insignificant change for thicker WE (L> 6?m)

Electroactivated Disposable Pencil Graphite Electrode – New, Cost‐effective, and Sensitive Electrochemical Detection of Bioflavonoid Hesperidin

AbstractIn this paper, for the first time, electroactivated disposable pencil graphite electrode (ePGE) was used for the detection of bioflavonoid hesperidin with cyclic and differential pulse voltammetry. The electroactivation efficiency of the pencil graphite electrode (PGE) was examined employing electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) and the enhancement of electron transfer kinetics of the PGE after the electroactivation was found. Hesperidin is irreversibly oxidized on the ePGE and its oxidation was the most pronounced at pH=5.0. Two electrode processes were detected, on one hand, a mixed diffusion and adsorption control was observed for the first electrode process. On the other hand, only diffusion control was observed in the second electrode process. Linear dependence between the peak current and the hesperidin concentration was obtained in the concentration range from 5×10−7 mol dm−3 to 1×10−5 mol dm−3 and the determined lower limit of detection (LOD) was 2×10−7 mol dm−3. Moreover, hesperidin in pharmaceutical formulation (containing active substance, hesperidin, and excipients) was quantified using ePGE. A good correlation was obtained between experimentally obtained hesperidin concentration by voltammetric analysis and concentration determined by standard HPLC technique (R2=0.9462).

In-Situ Monitoring of Electrode Degradation in Vanadium Redox-Flow Batteries By Distribution of Relaxation Times Analysis

Recent studies[1,2] suggest that ion crossover through the membrane of a vanadium redox-flow battery (VRFB) can not be considered the only source of irreversible capacity loss. Instead, degradation of the macroporous carbon felt electrodes has to be taken into account as well. Especially in the negative half-cell, any degradation-induced alteration of the fibres’ surface composition will significantly impede the kinetics of the V2+/V3+ redox-system. Since the resulting increase in kinetic overvoltage will limit the accessible capacity, a reasonable lifetime prediction of a VRFB is only possible if all aspects of capacity fade mechanisms, including electrode degradation are well understood. This raises the demand for a measurement technique, which allows for in-operando state-of-health-assessment of the electrodes in a non-invasive fashion. Employing electrochemical impedance spectroscopy (EIS), the characteristics of any electrochemical system can be easily probed by applying non-harmful, small-amplitude sinusoidal perturbations. Interpretation of EIS usually relies on fitting suitable equivalent circuit models to experimental data. However, validation of such models can be a cumbersome task due to the inherent ambiguity of EIS, meaning that different circuits may approximate the same data set equally well. Furthermore, a full cell spectrum will always yield a superposition of the respective half-cell impedances. Discriminating the contributions of the individual half-cell electrodes to the impedance of a VRFB has therefore been attempted by implementing reference electrodes. However, these are known to be a source of artefacts and distortion in the high frequency range.In the present study we apply the distribution of relaxation times (DRT) analysis[3] to EIS data of a single cell VRFB. This innovative approach allows us to resolve up to three different time constants per frequency decade. It therefore enables processes that overlap in the classical Bode- and Nyquist representation to be displayed as distinct peaks. Consequently, the individual half-cells can be studied from full cell spectra, circumventing the necessity of finding appropriate equivalent circuit models and rendering the implementation of reference electrodes obsolete.We outline our experimental strategy for unravelling the physical nature of the processes related to the individual signals in the DRT spectrum and finally demonstrate how these findings enable an online monitoring of electrode degradation in VRFB. Keywords: electrochemical impedance spectroscopy, distribution of relaxation times, electrode degradation, vanadium redox-flow battery

Synthesis and characterizations of air-cured polyurethane coatings from vegetable oils and itaconic acid

Polyurethane (PU) coatings were prepared using polyesteramide polyols based on different types of vegetable oils and itaconic acid. Long chain fatty diethanolamides were synthesized using the amidation of linseed/castor/karanja oils and the desired hydroxyl group was introduced via esterification reaction with itaconic acid to yield polyesteramide polyols. Its structural elucidation was carried out using Fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR). The study of crosslinking these polyols with hexamethylene diisocyanate (HDI-trimer and HDI-biuret) shows that the isocyanate structure and functionality contribute to the final polyurethane coatings properties. Various optical, mechanical, and durability performance of the cured PU metal coating films were examined. The gel content method was used to compare the crosslink density of various PU films. The thermal properties of the PU coating, including stability and glass transition temperature (Tg), were assessed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The corrosion resistance of PU coatings was analyzed by employing electrochemical impedance spectroscopy (EIS). PU metal coatings display superior gloss, adhesion, and chemical resistance properties. Differences in fatty acid compositions of linseed/castor/karanja oils were found to influence the air curing and mechanical and corrosion resistance properties of PU metal coatings. The use of itaconic acid and vegetable oils in the synthesis of these polyols contributes to their bio based characteristics and permits replacing the currently used petroleum-based polyols.

Construction of succinimide group substituted polythiophene polymer functionalized sensing platform for ultrasensitive detection of KLK 4 cancer biomarker

A novel impedimetric immunosensor based on conjugated succinimide group substituted polythiophene polymer (SucS-PThi) modified indium tin oxide (ITO) electrode was fabricated for ultra-sensitive and ultra-selective determination of kallikrein 4 (KLK 4) antigen in diluted human serum. The basic reason for the usage of SucS-PThi polymer was that its rich effective functional groups and biocompatibility. KLK 4, an important prostate biomarker was the target analyte and anti-KLK 4 antibodies immobilized electrode was the diagnostic tool for KLK 4 antigen detection. The fabricated biosensor was characterized by employing electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX), fourier transform-infrared (FTIR) and Raman spectroscopy. Under optimized conditions, a linear concentration range from 0.04 pg/mL to 30 pg/mL and a low detection limit (LOD) of 12.2 fg/mL were obtained and the LOD was lower than of most of the existing techniques, illustrating its feasibility for practical application. Moreover, the developed sensing system combined the outstanding properties in terms of selectivity, sensitivity, repeatability, reproducibility and reusability, without requiring for labor − intensive labeling stages. In addition, it was successfully utilized for accurate quantification of KLK 4 antigen in human serum samples.

Theoretical modeling and experimental studies of Terebinth extracts as green corrosion inhibitor for iron in 3% NaCl medium

In this study, essential oils (EOs) obtained from twigs, leaves and fruits of Terebinth (Pistacia terebinthus L.) was characterized by GC/MS analysis. We tested these as green corrosion inhibitors for iron in the neutral chloride medium (3% NaCl), employing electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) curves and surface characterizations SEM, EDX, IR spectroscopy were carried out. The theoretical aspect was elaborated using molecular dynamics (MD) simulation and density functional theory (DFT). Analyses of the experimental results showed that the three main components in the EOs from the twigs, fruits and leaves of Terebinth are α-Pinene (32.65–50.58%), Limonene (6.88–15.07%), and α-Terpineol (2.50–5.15%) with quantitative variations. The fruit EO at a concentration of 3000 ppm is characterized by the best anticorrosive protective properties than the leaf and twig EOs. Indeed, the optimum percentage of this EO required to achieve the maximum efficiency was found to be 86.4% at 3000 ppm. The surface investigation strategies (SEM-EDX and IR) further validated that the corrosion barrier happens because of the adsorption of the inhibitors over the iron/3% NaCl interface. Also, the outcomes of the theoretical approach supported all the experimental results by illustrating the similar trend of inhibition efficiencies of various inhibitors and revealed that Terebinth EOs could serve as an effective inhibitor of iron in 3% NaCl.

A label-free immunosensor for sensitive detection of RACK 1 cancer biomarker based on conjugated polymer modified ITO electrode

A new flexible biosensor based on conjugated polymer functionalized indium tin oxide (ITO) sheet was fabricated for Receptor for Activated C Kinase 1 (RACK 1) determination. Poly(3-thiophene acetic acid) (P(Thi-Ac)) was used as an immobilization matrix for construction of RACK 1 immunosensor. This polymer had a great number of carboxyl groups on its end site and these carboxyl ends provided anchoring points to the anti-RACK 1 antibodies. Anti-RACK 1 antibodies were covalently attached on the ITO electrode and recognized the RACK 1 antigens. Electrochemical characterizations were made by employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Additionally, single frequency impedance method (SFI) was applied to follow the specific biointeraction between antibody and antigen. As a result of specific biointeraction, the designed immunosensor exhibited a wide linear detection range between 0.01 pg/mL and 2 pg/mL RACK 1 with a detection limit of 3.1 fg/mL. Scanning electron microscopy and atomic force microscopy analyses were employed for electrode surface morphology investigation. The designed RACK 1 biosensor had good repeatability (5.73 %, RSD), excellent reproducibility (2.5 %, RSD), long storage-stability and reusable property. In addition, the fabricated RACK 1 biosensor was applied to determine RACK 1 concentration in human serums and the recovery was ranging from 98.79%–100.22%. This work illustrated a new tool to construct a sensitive and low-cost disposable biosensor for applications in clinical monitoring.

Adsorption of eco-friendly carthamus tinctorius on steel surface in saline solution: A combination of electrochemical and theoretical studies

In this study, the different parts of carthamus tinctorius plant, including petal (SPE), leaf (SLE), and shoot (SSE), have been extracted. Adsorption of the extracts on mild steel in 3.5 wt. % NaCl solution was evaluated employing electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and electrochemical noise measurements (EN). The field-emission scanning electron microscopy (FE-SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were employed to appraise the morphology of the samples surface subjected to the test solutions. According to the EIS results, the maximum adsorption efficiency belonged to the solution containing 1 g L−1 of petal extract. Polarization test results demonstrated a mixed-type inhibition with dominant anodic inhibition. The maximum inhibition efficiency resulted from SPE (84 %(while for the SLE and SSE it was around 60 % and 44 %, respectively. Moreover, the results obtained from FE-SEM showed that the organic compounds could effectively be adsorbed on the anodic sites and establish inhibitive film over the steel surface. Furthermore, molecular dynamics (MD) and Monte Carlo (MC) simulation methods applied on different components of the SPE revealed their adsorption onto steel substrates via donor-acceptor adhesion mechanism.

In-Situ Monitoring of Electrode Degradation in Vanadium Redox-Flow Batteries By Distribution of Relaxation Times Analysis

Recent studies[1,2] suggest that ion crossover through the membrane of a vanadium redox-flow battery (VRFB) can not be considered the only source of irreversible capacity loss. Instead, degradation of the macroporous carbon felt electrodes has to be taken into account as well. Especially in the negative half-cell, any degradation-induced alteration of the fibres’ surface composition will significantly impede the kinetics of the V2+/V3+ redox-system. Since the resulting increase in kinetic overvoltage will limit the accessible capacity, a reasonable lifetime prediction of a VRFB is only possible if all aspects of capacity fade mechanisms, including electrode degradation are well understood. This raises the demand for a measurement technique, which allows for in-operando state-of-health-assessment of the electrodes in a non-invasive fashion. Employing electrochemical impedance spectroscopy (EIS), the characteristics of any electrochemical system can be easily probed by applying non-harmful, small-amplitude sinusoidal perturbations. Interpretation of EIS usually relies on fitting suitable equivalent circuit models to experimental data. However, validation of such models can be a cumbersome task due to the inherent ambiguity of EIS, meaning that different circuits may approximate the same data set equally well. Furthermore, a full cell spectrum will always yield a superposition of the respective half-cell impedances. Discriminating the contributions of the individual half-cell electrodes to the impedance of a VRFB has therefore been attempted by implementing reference electrodes. However, these are known to be a source of artefacts and distortion in the high frequency range.In the present study we apply the distribution of relaxation times (DRT) analysis[3] to EIS data of a single cell VRFB. This innovative approach allows us to resolve up to three different time constants per frequency decade. It therefore enables processes that overlap in the classical Bode- and Nyquist representation to be displayed as distinct peaks. Consequently, the individual half-cells can be studied from full cell spectra, circumventing the necessity of finding appropriate equivalent circuit models and rendering the implementation of reference electrodes obsolete.We outline our experimental strategy for unravelling the physical nature of the processes related to the individual signals in the DRT spectrum and finally demonstrate how these findings enable an online monitoring of electrode degradation in VRFB. Keywords: electrochemical impedance spectroscopy, distribution of relaxation times, electrode degradation, vanadium redox-flow battery

Effect of voltage on microstructure and its influence on corrosion and tribological properties of TiO2 coatings

To improve the corrosion resistance performance of TiO2 thin films, a coating was prepared on 316 L stainless steel substrate following the electrophoretic deposition process. The structural, surface composition and morphological compositions of TiO2 films were analyzed by Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD), respectively. Micro-scratch tester was used to investigate the tribological properties and corrosion performance was examined employing electrochemical impedance spectroscopy (EIS) and Potentiodynamic polarization in 3.5 wt.% aqueous NaCl solution. Among the three coatings produced at three different applied voltages, film obtained under 30 V exhibited the lowest corrosion current density value of 0.212 µA as well as the highest charge transfer resistance (the corrosion resistance) and the double layer capacitance, which was attributed mainly to the significant decrease of micro-pore into the film.