Theoretical Analysis of an Amperometric Biosensor Based on Parallel Substrates Conversion

The behaviour of an amperometric biosensor based on parallel substrates conversion for steady-state condition has been discussed. This analysis contains a nonlinear term related to enzyme kinetics. Simple and closed form of analytical expressions of concentrations and of biosensor current is derived. This model was originally reported by Vytautas Aseris and his team (2012). Concentrations of substrate and product are expressed in terms of single dimensionless parameter. A new approach to Homotopy perturbation method (HPM) is employed to solve the system of nonlinear reaction diffusion equations. Furthermore, in this work, the numerical solution of the problem is also reported using Matlab program. The analytical results are compared with the numerical results. The analytical result provided is reliable and efficient to understand the behavior of the system.

A CV Study of Copper Complexation with Guanine Using Glassy Carbon Electrode in Aqueous Medium

Voltammetric behaviors of Copper (II) nitrogen bearing nucleobases, such as Guanine (C5H4N5O2) was studied in electro analyzer using cyclic voltammetry (CV) on a Glassy Carbon Electrode. Assessment of the chemical and physical conditions that may favor optimum current enhancement was done by studying the effect of variation of concentration of metal and ligand ions, variation of scan rate, variation of step height, variation of pH values, and variation of supporting electrolyte as (NH4)2SO4, KCl, and NaCl. It was observed that Copper and Guanine forms a 1 : 2 ratio complex. The work reflects that increasing the concentration of either metal ion or ligand ion increases the corresponding current. Increasing the scan rate increases the corresponding current linearly with the square root of the scan rate. As the step height decreases the peaks become sharp. Anodic and cathodic current increases linearly with decreasing step height. For the complex mixture the complexation occurs maximum at a pH of 2.3–7.0 and is badly restricted in the slightly alkaline medium and the complexing order of the supporting electrolyte showed a trend as (NH4)2SO4>NaCl>KCl.

Reduced Graphene Oxide Supported Antimony Species for High-Performance Supercapacitor Electrodes

Antimony species was chemically anchored on graphene oxide using antimony (III) chloride precursor and then converted to the reduced graphene oxide-antimony species composite by a well-established polyol method. The resultant composite was successfully used as supercapacitor electrodes in a two-electrode symmetric system with aqueous electrolyte. The specific capacitance calculated from the galvanostatic charge/discharge curves obtained for this composite was 289 F/g. The enhanced capacitance results were confirmed by the electrochemical impedance spectroscopy and cyclic voltammetry. The high capacitance of the reduced graphene oxide-antimony species composite arises from the combination of double-layer charging and pseudocapacitance caused by the Faradaic reactions of the intercalated antimony species and residual surface-bonded functional groups.

Enhanced Structural Integrity and Electrochemical Performance of AlPO4-Coated MoO2 Anode Material for Lithium-Ion Batteries

AlPO4 nanoparticles were synthesized via chemical deposition method and used for the surface modification of MoO2 to improve its structural stability and electrochemical performance. Structure and surface morphology of pristine and AlPO4-coated MoO2 anode material were characterized by electron microscopy imaging (SEM and TEM) and X-ray diffraction (XRD). AlPO4 nanoparticles were observed, covering the surface of MoO2. Surface analyses show that the synthesized AlPO4 is amorphous, and the surface modification with AlPO4 does not result in a distortion of the lattice structure of MoO2. The electrochemical properties of pristine and AlPO4-coated MoO2 were characterized in the voltage range of 0.01–2.5 V versus Li/Li+. Cyclic voltammetry studies indicate that the improvement in electrochemical performance of the AlPO4-coated anode material was attributed to the stabilization of the lattice structure during lithiation. Galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) studies reveal that the AlPO4 nanoparticle coating improves the rate capability and cycle stability and contributes toward decreasing surface layer and charge-transfer resistances. These results suggest that surface modification with AlPO4 nanoparticles suppresses the elimination of oxygen vacancies in the lattice structure during cycling, leading to a better rate performance and cycle life.

Electrochemical Investigation on Adsorption of Fluconazole at Mild Steel/HCl Acid Interface as Corrosion Inhibitor

The interfacial behavior of fluconazole on mild steel in 1 M HCl solution was studied by electrochemical methods, namely, polarization (Tafel Plot) and Electrochemical Impedance Spectroscopy (EIS). The surface morphology of mild steel in the presence and absence of fluconazole was studied by Atomic Force Microscopy (AFM). The results of the study showed that fluconazole reduced the corrosion rate in HCl acid solution by adsorbing on the surface of mild steel. Tafel results suggest that fluconazole behaves predominantly as an anodic inhibitor and shows greater inhibition efficiency (96%) at 0.30 mM. Thermodynamical parameters suggest that fluconazole is adsorbed on mild steel mainly by chemical mode. The EIS studies reveal the formation of a thin barrier film on mild steel surface. The AFM image of mild steel immersed in optimum concentration of fluconazole has confirmed the film formation on metal surface.

Comparison of Single-Walled and Multiwalled Carbon Nanotubes Durability as Pt Support in Gas Diffusion Electrodes

Durability of single-walled (SWCNT) and multiwalled carbon nanotubes (MWCNT) as Pt supports was studied using two accelerated durability tests (ADTs), potential cycling and potentiostatic treatment. ADT of gas diffusion electrodes (GDEs) was once studied during the potential cycling. Pt surface area loss with increasing the potential cycling numbers for GDE using SWCNT was shown to be higher than that for GDE using MWCNT. In addition, equilibrium concentrations of dissolved Pt species from GDEs in 1.0 M H2SO4 were found to be increased with increasing the potential cycling numbers. Both findings suggest that Pt detachment from support surface plays an important role in Pt surface loss in proton exchange membrane fuel cell electrodes. ADT of GDEs was also studied following the potentiostatic treatments up to 24 h under the following conditions: argon purged, 1.0 M H2SO4, 60°C, and a constant potential of 0.9 V. The subsequent electrochemical characterization suggests that GDE that uses MWCNT/Pt is electrochemically more stable than other GDE using SWCNT/Pt. As a result of high corrosion resistance, GDE that uses MWCNT/Pt shows lower loss of Pt surface area and oxygen reduction reaction activity when used as fuel cell catalyst. The results also showed that potential cycling accelerates the rate of surface area loss.

High Performance PEM Fuel Cell with Low Platinum Loading at the Cathode Using Magnetron Sputter Deposition

Platinum cluster formations have been investigated as a way to reduce the amount of Pt at the cathode of polymer electrolyte membrane fuel cells. One, two, and three layers of Pt (0.05 mg/cm2) sputtered directly on microporous layers of gas diffusion layers with and without interfacial carbon-Nafion layers and carbon-polytetrafluoroethylene (CPTFE) layers have been used as a cathode. Comparison with experimental results had showed that the best performance was obtained with three layers of Pt sputtered on carbon-Nafion containing 34.8 wt.% of Nafion and sputtered carbon-polytetrafluoroethylene containing 16.9 wt.% of polytetrafluoroethylene. High limiting current densities (>1.1 A/cm2) have been reached with cathode Pt loading as low as 0.05 mg/cm2. SEM imagery and cyclic voltammetry characterization have been performed to consolidate this study. High Pt utilization can be showed by this method. The factor influencing Pt utilisation in the oxygen reduction reaction is intrinsically related to Pt clusters formation and helps in enhancing the PEMFC performance with low Pt loading.

Electrodialysis of Phosphates in Industrial-Grade Phosphoric Acid

The objective of this research was to study the purification of industrial-grade phosphoric acid (P2O5) by conventional electrodialysis. The experiments were conducted using a three-compartment cell with anion and cation membranes, and industrial acid solution was introduced into the central compartment. The elemental analysis of the diluted solution indicated that the composition of magnesium, phosphates, and sodium was reduced in the central compartment. The ratios of the concentration of the ions and the phosphates were essentially unchanged by the process. Consequently, electrodialysis could not purify the acid in the central compartment, and the migration of phosphate ions to the anolyte produced a highly concentrated phosphoric acid solution containing sulfates and chlorides as impurities. However, the migration of the phosphate ions across the membrane consumed a large amount of energy. Detailed speciation diagrams were constructed in this study. These diagrams showed that metal-phosphate complexes were predominant in the industrial phosphoric acid solution. This result explains why the ratios of the concentrations of the ion metals and the phosphates did not change in the purification process. The energy consumed in the electrodialysis indicated that the metal-phosphate complexes were less mobile than the free-phosphate ions. The speciation diagrams explained the experimental results satisfactorily.

Electrochemical and Surface Morphological Studies of Carbon Steel Corrosion by a Novel Polynuclear Schiff Base in HCl Solution

The corrosion inhibition efficiency of a potential polynuclear Schiff base, (s)-2-(anthracene-9 (10H)-ylidene amino)-5-guanidinopentanoic acid (A9Y5GPA), on carbon steel (CS) in 1 M hydrochloric acid solution has been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization studies. The corrosion inhibition efficiencies of parent amine [(s)-2-amino-5-guanidinopentanoic acid] and parent ketone (anthracene-9 (10H)-one) on carbon steel in 1.0 M hydrochloric acid solution have also been investigated using weight loss studies. The electrochemical and weight loss data established that the inhibition efficiency on CS increases with the increase in the concentration of inhibitor, A9Y5GPA. The adsorption of A9Y5GPA obeys the Langmuir adsorption isotherm. Thermodynamic parameters (Kads, ΔGads0) were calculated using the adsorption isotherm. Activation parameters of the corrosion process (Ea, ΔH* and ΔS*) were also calculated from the corrosion rates obtained from temperature studies. Tafel plot analysis revealed that A9Y5GPA acts as a mixed-type inhibitor. A probable inhibition mechanism was also proposed. Surface morphology of the carbon steel specimens in the presence and absence of the inhibitor was evaluated by SEM analysis.

An Immunosensor for Pathogenic Staphylococcus aureus Based on Antibody Modified Aminophenyl-Au Electrode

The objective of this work is to elaborate an immunosensing system which will detect and quantify Staphylococcus aureus bacteria. A gold electrode was modified by electrografting of 4-nitrophenyl diazonium, in situ synthesized in acidic aqueous solution. The immunosensor was fabricated by immobilizing affinity-purified polyclonal anti S. aureus antibodies on the modified gold electrode. Cyclic voltammetry (CV) and Faradaic Electrochemical Impedance Spectroscopy (EIS) were employed to characterize the stepwise assembly of the immunosensor. The performance of the developed immunosensor was evaluated by monitoring the electron-transfer resistance detected using Faradaic EIS. The experimental results indicated a linear relationship between the relative variation of the electron transfer resistance and the logarithmic value of S. aureus concentration, with a slope of 0.40 ± 0.08 per decade of concentration. A low quantification limit of 10±2 CFU per ml and a linear range up to 107±2×106 CFU per mL were obtained. The developed immunosensors showed high selectivity to Escherichia coli and Staphylococcus saprophyticus.