Impedimetric Measurements for Monitoring Avidin-Biotin Interaction on Self-Assembled Monolayer

Avidin-biotin has been controllable immobilized on the surface of gold electrodes using mercaptopropionic acid as self-assembled monolayer. Electrochemical impedance spectroscopy (EIS) was employed to investigate the changes that appear at the electrode surface in the presence of a redox mediator, K₃[Fe(CN)₆]. An electrical model more complex than that in other studies was used to interpret the EIS measurements (Randles circuit). This model is very useful because it takes into consideration both the transfer of electrons at the electrode/electrolyte interface and the diffusion of redox species through the double layer. The model allowed us to determine some important parameters like solution resistance R_sol, charge-transfer resistance R_ct, double-layer capacitance C_dl, Warburg resistance R_W, and the diffusion time constant τ. The EIS results proved that immobilization of avidin-biotin increased the charge-transfer resistance R_ct, due to the insulating character of these molecules.     

Enhanced photoelectrochemical properties and photocatalytic activity of porous TiO2 films with highly dispersed small Au nanoparticles

Small Au nanoparticles (NPs) with mean diameter of 4.1 nm were highly deposited on TiO₂ films via a simple electrostatic self-assembly method. The physically separated Au NPs, with a high surface density of 6.3 × 10¹¹ NPs/cm², were mainly distributed on the top layer of porous TiO₂ films. The deposition of Au NPs induced a negative shift (~ 100 mV) of the apparent flat band potential of Au-TiO₂ electrodes. The charge separation efficiency of the TiO₂ electrode increased from 72.1% to 88.5% by dispersing Au NPs. Whatever redox species were present in the electrolyte, the Au-TiO₂ electrode had higher photovoltage than the TiO₂ electrode. The photovoltage was very sensitive to added redox species such as O₂, O₃, and methanol, and the effect of adsorbed redox species on electron accumulation was discussed. The electrochemical impedance spectroscopic measurements revealed that the charge transfer resistance (R_ct) of Au-TiO₂ films was reduced to 16% of bare TiO₂ electrode, and the decreased R_ct corresponded to the increased photocatalytic activity of Au-TiO₂ films. The beneficial role of uniformly dispersed small Au NPs on the charge separation was discussed. By modifying TiO₂ films with small Au NPs, the photocatalytic activity of TiO₂ films for formaldehyde degradation increased about 2.5 times.     

The mechanism of specific capacitance improvement of supercapacitors based on MnO2 at an elevated operating temperature

Amorphous nanostructured MnO₂ film was anodically deposited onto economical duplex stainless steel substrate. The obtained MnO₂ film was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy for microstructural, morphological, and compositional studies. The capacitive behavior was systematically investigated by cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectroscopy (EIS) in 1 M Na₂SO₄ electrolyte at different operating temperatures ranging from 20 to 60 °C. The specific capacitance (SC) was improved with an increase of operating temperature, and the highest SC of 398 F/g was achieved at a scan rate of 10 mV/s and operating temperature of 60 °C. The mechanism of SC improvement at elevated operating temperature was investigated using EIS. With an increase of operating temperature, the conductivity of electrolyte was improved, and the charge-transfer resistance (R_ct) was decreased. The temperature dependence of 1/R_ct follows an Arrhenius equation. The MnO₂ film was electrochemically activated at 60 °C due to the formation of Na_yMnO₂ after discharging.     

Cadmium-sensitive electrode based on tetracetone derivatives of p-tert-butylcalix[8]arene

The performance of a cadmium-sensitive electrode based on the tetracetone derivatives of p-tert butylcalix[8]arene was investigated. The ion-sensitivity of the calix[8]arene was examined via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectrometry, UV/Vis spectroscopy and FT-IR spectroscopy. The sensitive membrane containing the active ionophore was cast onto the surface of a gold electrode. The electrode exhibited a linear relationship between the charge transfer resistance (R_ct) and the logarithm of the detected ion concentration. The cathodic peak at a potential of 0.56 V increased linearly as the Cd^2 + ion concentration increased. The detection limit of the device reached 10^? 7 M with high sensitivity toward cadmium.     

Microbially influenced corrosion of stainless steel by marine bacterium Vibrio natriegens: (I) Corrosion behavior

The microbially influenced corrosion of stainless steel (SS) by marine bacterium Vibrio natriegens (V. natriegens) was investigated using surface analysis (atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDXA)) and electrochemical techniques (the open circuit potential, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves ). AFM images corroborated the results from the EIS models which show biofilm attachment and subsequent detachment over time. The SEM images revealed the occurrence of micro-pitting corrosion underneath the biofilms on the metal surface after the biofilm removal. The presence of carbon, oxygen, phosphor and sulfur obtained from EDXA proved the formation of biofilm. The electrochemical results showed that the corrosion of SS was accelerated in the presence of V. natriegens based on the decrease in the resistance of the charge transfer resistance (R_ct) obtained from EIS and the increase in corrosion current densities obtained from potentiodynamic polarization curves.     

Evaluation of the Corrosion Protection Performance of Epoxy-Coated High Manganese Steel by SECM and EIS Techniques

The corrosion protection performances of epoxy-coated Mn steel and carbon steel were evaluated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis. EIS was performed on coated Mn steel with a scratch in a 0.1 M NaCl solution after a wet/dry cyclic corrosion test. The charge transfer resistance (R _ct) and film resistance (R _f) of the coated Mn steel displayed a higher value than the coated carbon steel. The increase in the charge transfer resistance and film resistance of the coated steel is due to the presence Mn in steel. SECM was conducted to estimate the corrosion protection performance of the epoxy-coated Mn steel immersed in a 0.1 M NaCl solution. It was found that dissolution of Fe²⁺ was suppressed at the scratch on the coated Mn steel due to the higher resistance for anodic dissolution of the substrate. SEM/EDX analysis showed that Mn was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layer of Mn in the rust of the steel, which had a beneficial effect on the corrosion resistance of the coated steel by forming protective corrosion products in the wet/dry cyclic test.     

A facile method to synthesize carbon coated Li1.2Ni0.2Mn0.6O2 with improved performance

Carbon-coated Li_1.2Ni_0.2Mn_0.6O₂ powders have been synthesized with Bakelite and heat process in air. The effect of carbon coating on the physical and electrochemical properties have been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), discharge and rate tests. The carbon-coated cathode exhibits much improved first discharge capacity and rate capability than the pristine sample. The discharge capacity at 0.1 and 5.0 C rates are 246 and 125 mAhg⁻¹, while that of pristine are only about 222 and 49 mAhg⁻¹, respectively. The capacity retention of Li_1.2Ni_0.2Mn_0.6O₂ electrode after 50 cycles is improved from 89.8 to 97.5% after carbon coating. EIS results indicate that R_ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode is decreased from 62 to 37 Ω after carbon coating.     

The influence of SiC particles on the corrosion resistance of electroless,Cu–P composite coating in 1 M HCl

The present paper aims to compare the corrosion resistance of the electroless Cu–P–SiC with Cu–P composite coating on carbon steel in 1 M HCl solution by the weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopic (EIS) techniques. The study reveals that, the corrosion current density (I_corr) and the double layer capacitance (C_dl) values decrease, the charge transfer resistance (R_ct) and inhibition of efficiencies (IE %) increase with the incorporation of SiC particles in the Cu–P matrix indicating the improvement in corrosion resistance.     

Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms

An antibacterial 2205-Cu duplex stainless steel(DSS)was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu~(2+)ions from the2205-Cu DSS surface.In this work,the microbiologically influenced corrosion(MIC)resistance of 2205-Cu DSS in the presence of the corrosive marine bacterium Pseudomonas aeruginosa was investigated.The addition of copper improved the mechanical properties such as the yield strength,the tensile strength and the hardness of 2205 DSS.Electrochemical test results from linear polarization resistance(LPR),electrochemical impedance spectroscopy(EIS)and critical pitting temperature(CPT)measurements showed that 2205-Cu DSS possessed a larger polarization resistance(R_p),charge transfer resistance(R_(ct))and CPT values,indicating the excellent MIC resistance of 2205-Cu DSS against the corrosive P.aeruginosa biofilm.The live/dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS.The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14 d in the presence of P.aeruginosa(2.2μm vs 12.5μm).2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P.aeruginosa.     

Low temperature performance of graphite and LiNi0.6Co0.2Mn0.2O2 electrodes in Li-ion batteries

Low temperature (LT) behavior of graphite/LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cells prepared with low loading or LL (thinner electrodes prepared with low loading and packing density) and high loading or HL (thicker electrodes prepared with high loading and packing density) were investigated. The cells were prepared as half coin cell, full coin cell, and full pouch cell to identify the main factors that limit LT operations of lithium ion batteries. All the cells were tested at ?32 °C, and the capacity retention at LT was compared to the capacity retention at room temperature (RT). The Li⁺ insertion kinetics was analyzed by electrochemical impedance spectroscopy. The LL electrodes showed a lesser charge transfer resistance (R _ct) than that shown by the thicker electrodes at LT. The diffusion coefficients of Li⁺ calculated via the galvanostatic intermittent titration technique (GITT) in graphite and NCM622 electrodes prepared with LL and HL at RT were in the range of 10^?8 cm²/s but decreased to the range of 10^?13 and 10^?11 cm²/s at ?32 °C, respectively. GITT results confirmed that the capacity loss at LT, with increased electrode loading, arose from the limitation of Li-ion diffusion within the electrode.     

Time-Resolved Electrochemical Impedance Spectroscopy of Stochastic Nanoparticle Collision: Short Time Fourier Transform versus Continuous Wavelet Transform

This work demonstrates the utilization of short-time Fourier transform (STFT), and continuous wavelet transform (CWT) electrochemical impedance spectroscopy (EIS) for time-resolved analysis of stochastic collision events of platinum nanoparticles (NPs) onto gold ultramicroelectrode (UME). The enhanced electrocatalytic activity is observed in both chronoamperometry (CA) and EIS. CA provides the impact moment and rough estimation of the size of NPs. The quantitative information such as charge transfer resistance (R_ct) relevant to the exchange current density of a single Pt NP is estimated from EIS. The CWT analysis of the phase angle parameter is better for NP collision detection in terms of time resolution compared to the STFT method.     

Electrochemical behavior of biocompatible AZ31 magnesium alloy in simulated body fluid

Dense oxidation coatings have been successfully developed on biocompatible AZ31 magnesium alloy, using microarc oxidation technique, to improve the corrosion resistance. Three different deposition voltages of 250, 300, and 350 V have been employed. The effect of voltage on the coating corrosion resistance has been evaluated through electrochemical experiments in a simulated body fluid (SBF) up to 7 days. Potentiodynamic polarization and electrochemical impedance spectroscopy scans were performed in the SBF solution, followed by optical microscopy surface inspection. The results indicate that the corrosion rates of the coatings are in the order of 250 < 300 < 350 V after immersion for 7 days, and the charge transfer resistance (R _ct) of the three samples is in the order of 250 > 300 > 350 V. Both the electrochemical tests and the surface inspection suggest that the 250 V coating has the highest corrosion resistance, with lowest corrosion current density, highest R _ct, and the best surface quality.     

Characterization and photocatalytic activity of nanostructured indium tin oxide thin-film electrode for azo-dye degradation

Photocatalytically active indium tin oxide thin film electrodes were prepared by electron beam evaporation technique onto a glass substrate having thickness 120 nm. Degradation of reactive dye yellow direct 42 has been performed using photoeletrocatalysis. A biased potential is applied across indium tin oxide photoelectrode illuminated by UV light. The best experimental conditions were found to be dye concentration 1.0 × 10^− 5 mol L^− 1, pH 5.25 and 0.5 mol L^− 1 NaCl as supporting electrolyte when the photoelectrode was biased at + 0.5 V versus saturated calomel electrode. The effects of other electrolytes, dye concentration, pH solution, electrode annealing temperature and applied potentials have been also investigated and are discussed. Several common inorganic salts Na₂SO₄, Na₂CO₃, NaNO₃ and NaCl were chosen to act as supporting electrolytes, which was added into the dye solution. It is shown that the charge-transfer resistance of photoanode can be calculated by the analysis of its electrochemical impedance spectroscopy, and the photoelectrocatalytic degradation rate of yellow direct 42 was inversely proportional to the value of charge-transfer resistance of photoelectrodes at different pH. The value of charge-transfer resistance is smaller, the higher its photoelectro-activity is.     

Mechanical,tribological and anti-corrosive properties of polyaniline/graphene coated Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys

The mechanical, tribological and corrosion protection offered to Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys by the epoxy coating containing polyaniline/graphene (PANI/Gr) pigments is undertaken in the current work. PANI/Gr containing coatings were observed to be strongly adherent with a higher scratch hardness (H_s) and plowing hardness (H_p), i.e. H_s of 0.43 GPa, and H_p of 0.61 GPa, respectively when compared to that of neat epoxy coating (H_s of 0.17 GPa, and H_p of 0.40 GPa, respectively). Due to their higher H_s and H_p values, PANI/Gr based coatings displayed an enhanced wear resistance (Wear volume, W_v = 4.53 × 10^-3 m³) than that of neat epoxy coating (W_v = 5.15 × 10⁻³ m³). The corrosion protection efficiency in corrosive environment of 3.5 wt% NaCl solution was obtained to be >99% for PANI/Gr containing coatings when compared to that of neat epoxy coating. The charge-transfer resistance (R_ct) of the PANI/Gr containing coatings were estimated to be >10⁶ Ω cm², which indicates their highly protective nature when compared to that of neat epoxy coating (R_ct ˜10⁵ Ω cm²). Hence, PANI/Gr containing coatings can be potentially used for wear resistance and corrosion protection applications in marine environments.     

Effect of bias voltage on the electrochemical properties of TiN coating for polymer electrolyte membrane fuel cell

The electrochemical properties of TiN film coated on AISI 316 stainless steel (SS) by the magnetron sputtering physical vapor deposition (PVD) were studied for application as a bipolar plate. The crystal structure and surface morphology of the coatings were examined by x-ray diffractometry (XRD) and atomic force microscopy (AFM), respectively. The corrosion behaviors of the TiN films were investigated by electrochemical methods, including potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) under + 600 mV_SCE application. The electrochemical behavior of the TiN coatings was enhanced with increasing bias voltage due to lower corrosion current density and higher R_ct values during an immersion time of 168 h. This result was attributed to the formation of crystalline-refined TiN(200) at high bias voltage, which increased the coating compactness and the protective efficiency, and decreased passive current density.     

The electrochemical properties of MgNi–x?wt% TiNi0.56Co0.44 (x?=?0, 10, 30, 50) composite alloys

The effect of ball milling time and different content of the TiNi_0.56Co_0.44 alloy on the structure and electrochemical properties of MgNi–x wt% TiNi_0.56Co_0.44 (x = 0, 10, 30, 50) alloys were studied systematically. The results indicated that the cycle durability of the alloy was improved with addition of the TiNi_0.56Co_0.44 alloy. By cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis, it was shown that the introduction of the TiNi_0.56Co_0.44 alloy could significantly improve the catalytic activity of the electrode, decrease the charge-transfer reaction resistance and the diffusion impedance of H atoms. Potentiodynamic polarization curves revealed that anti-corrosion performance of the composite electrodes was enhanced, which was responsible for the ameliorative cycle stability of composite alloys. A high discharge capacity and good cycle stability had been observed for the x = 10 (10 h) composite electrode with a maximum discharge capacity of 397 mAh/g and capacity retaining rate (S ₅₀) of 62%.     

Comparative corrosion study of Ag-Pd and Co-Cr alloys used in dental applications

The electrochemical behaviour of two Ag-Pd alloys (Unique White and Paliag) used in dental prosthetics construction for crowns and bridges and one Co-Cr alloy (Vitallium 2000) was studied in artificial saliva using the polarization curves and electrochemical impedance spectroscopy (EIS). The corrosion resistance was evaluated by means of the corrosion currents value and by coulometric analysis. The open circuit potential of Ag-Pd are attributed to dealloying followed by surface enrichment with Ag and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. Our results have shown that these alloys have a somewhat good corrosion resistance in artificial saliva. The corrosion current densities of Unique White and Vitallium 2000 alloys were very low (∼100 nA/cm²). For Ag-Pd alloys, when increasing the content of Cu, corrosion resistance decreases. The passivation of all samples occurred spontaneously at the open circuit potential. The electrochemical properties of the spontaneously passivated electrodes at the open circuit potential were studied by EIS. The polarization resistance (R _p) and the electrode capacitance (C _dl) were determined. The polarization resistance of all the samples increases with the immersion time. The polarization resistances are largest for Unique White (Ag-Pd) and Vitallium 2000 (Co-Cr) alloys. Because the electrochemical behaviour of the Co-Cr alloy was compared with that of Ag-Pd alloy, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses. The present study, though limited, has shown that electrochemical characteristics can be used to identify such alloys. Knowledge of the in vitro corrosion behaviour of these alloys may lead to better understanding of any biologically adverse effects in vitro.     

Microbiologically influenced corrosion of titanium caused by aerobic marine bacterium Pseudomonas aeruginosa

Microbiologically influenced corrosion (MIC) is a big threat to the strength and safety of many metallic materials used in different environments throughout the world. The metabolites and bioactivity of the microorganisms cause severe deterioration on the metals. In this study, MIC of pure titanium (Ti) was studied in the presence of a highly corrosive aerobic marine bacterium Pseudomonas aeruginosa. The results obtained from electrochemical test showed that Ti was corrosion resistant in the abiotic culture medium after 14 d, while the increased corrosion current density (i_corr) obtained from polarization curves and the decreased charge transfer resistance (R_ct) from electrochemical impedance spectroscopy (EIS) indicated the accelerated corrosion of Ti caused by P. aeruginosa biofilm. For further confirmation of the above results, the surface of Ti was investigated using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). According to the XPS results, TiO₂ was formed in both abiotic and biotic conditions, while unstable oxide Ti₂O₃ was detected in the presence of P. aeruginosa, leading to the defects in the passive film and localized corrosion. Pitting corrosion was investigated with the help of CLSM, and the largest pit depth found on Ti surface immersed in P. aeruginosa was 1.2 μm. Ti was not immune to MIC caused by P. aeruginosa.     

Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy study of the response mechanism of the chalcogenide glass membrane iron(III) ion-selective electrode in saline media

The response mechanism of the iron(III) chalcogenide glass membrane ion-selective electrode (ISE) in saline media has been studied using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). EIS equivalent circuits and XPS surface compositions for the FeIII ISE are consistent with the presence of two surface films probably comprising a outer surface layer (OSL) and an Fe-deficient modified surface layer (MSL), along with a low-frequency charge-transfer impedance that is attributable to the reduction of Fe3+. In accordance with literature data for the conductivity of low-bearing iron(III) chalcogenide glasses, a high-impedance MSL is internally consistent with XPS data for an Fe-deficient MSL. It is evident that the impedance of the MSL diminishes on exposure to solutions containing Fe3+, and this finding is consistent with the ion exchange of Fe3+ within the MSL. Likewise, the charge-transfer impedance also decreases at elevated levels of Fe3+, demonstrating that Fe3+ is a participant in the reversible charge-transfer reaction occurring at the electrolyte/electrode interface. The kinetics of charge transfer are facilitated by Fe chelating agents (e.g., citrate, salicylate, EDTA, etc.) due presumably to the complexation of the products of the charge transfer process (possibly Fe2+). It is shown unequivocally that the response of the FeIII ISE in saline buffers is independent of pH, demonstrating that the ISE is responding directly to Fe3+, not H+. A mechanism involving a combination of charge transfer and ion exchange of FeIII, at the electrode diffusion layer, has been proposed to explain the 30 mV/decade slope of the FeIII ISE.     

Study on Li-ion diffusion in nano-crystalline LiMn2O4 thin film cathode grown by pulsed laser deposition using CV, EIS and PITT techniques

In the present work, LiMn₂O₄ thin films have been prepared by pulsed laser deposition on stainless steel substrates. The films deposited at 400 °C and 200 mTorr of oxygen were mainly composed of nano-crystals less than 100 nm and their agglomerates. Three different electrochemical methods including CV, EIS and PITT were applied to measure the overall Li⁺-ion diffusion coefficients and charge-transfer resistances at various potentials from 3.85 to 4.5 V. The Li⁺ diffusion coefficients were in the range of 10⁻¹² to 10⁻¹⁰ cm² s⁻¹, depending on the potentials. It was found that the charge-transfer resistances decreased with the increase of potentials. Especially, relatively high diffusion coefficients and low charge-transfer resistances were observed above 4.2 V.