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Charge Transfer Resistance (charge + transfer_resistance)
Selected AbstractsA New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon NanotubesELECTROANALYSIS, Issue 9 2009Cruz Moraes, Fernando Abstract The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700,mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12,,mol L,1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection. [source] Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self-Assembled Alkanethiol Monolayer on Gold ElectrodeELECTROANALYSIS, Issue 2 2009Dan Zheng Abstract A stable ordered mesoporous carbon (OMC) film electrode was successfully constructed by adsorbing OMC onto a self-assembled monolayer (SAM) of C18H37SH chemisorbed on the Au electrode. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrochemical methods were used to characterize the properties of the OMC film electrode. The adsorbed OMC can restore the heterogeneous electron transfer almost totally blocked by the alkanethiol monolayer. Nyquist plots show a sharply decrease of the charge transfer resistance (Rct) of the Fe(CN) couple at the OMC film electrode. Furthermore, the OMC film electrode is found to possess a significantly reduced interfacial capacitance and largely enhanced current response of hydrogen peroxide. This novel approach to the fabrication of stable OMC film electrode with excellent electrochemical properties is believed to be very attractive for electrochemical studies and electroanalytical applications. [source] Power Generation and Electrochemical Analysis of Biocathode Microbial Fuel Cell Using Graphite Fibre Brush as Cathode MaterialFUEL CELLS, Issue 5 2009S.-J. You Abstract To improve cathodic efficiency and sustainability of microbial fuel cell (MFC), graphite fibre brush (GFB) was examined as cathode material for power production in biocatalysed-cathode MFC. Following 133-h mixed culturing of electricity-producing bacteria, the MFC could generate a reproducible voltage of 0.4,V at external resistance (REX) of 100,,. Maximum volumetric power density of 68.4,W,m,3 was obtained at a current density of 178.6,A,m,3. Upon aerobic inoculation of electrochemically active bacteria, charge transfer resistance of the cathode was decreased from 188 to 17,, as indicated by electrochemical impedance spectroscopy (EIS) analysis. Comparing investigations of different cathode materials demonstrated that biocatalysed GFB had better performance in terms of half-cell polarisation, power and Coulombic efficiency (CE) over other tested materials. Additionally, pH deviation of electrolyte in anode and cathode was also observed. This study provides a demonstration of GFB used as biocathode material in MFC for more efficient and sustainable electricity recovery from organic substances. [source] Impeding corrosion of sintered NdFeB magnets with titanium nitride coatingMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2010A. Ali Abstract Sintered NdFeB magnets have poor corrosion resistance that renders them susceptible to corrosion in industrial and marine environments. This paper evaluates the properties of cathodic arc physical vapour deposited (CAPVD) titanium nitride coating for corrosion protection of sintered NdFeB permanent magnets. The performance of titanium nitride coating has been compared to the electrodeposited nickel,copper,nickel multilayer coating. The rates of coatings degradation in simulated marine environment were estimated with electrochemical impedance spectroscopy (EIS). Cyclic polarization was carried out to assess the pitting potential. The surface chemistry and coating morphologies were studied with scanning electron microscope (SEM). X-ray diffraction (XRD) was used for qualitative phase analyses of coatings and the substrate. It was figured out that the charge transfer resistance of CAPVD titanium nitride coating increased with exposure time. The negative rate of Rp-degradation for titanium nitride coating compared to the nickel,copper,nickel multilayer for equivalent exposure time is a unique and valuable result. Polarization results showed that ,pits re-passivation' of titanium nitride coating could be responsible for the extended corrosion protection of the NdFeB substrate. The magnetic properties remained comparable for both types of coatings. [source] Electrochemistry and XPS study of an imidazoline as corrosion inhibitor of mild steel in an acidic environmentMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2009O. Olivares-Xometl Abstract The effect of 2-(2-heptadec-8-enyl-4,5-dihydro-imidazol-1-yl)-ethylamine on the corrosion behavior of mild steel in aqueous hydrochloric acid was investigated using weight loss measurements, polarization scans, electrochemical impedance, and X-ray photoelectron spectroscopy (XPS). The inhibition efficiencies and coverage degrees increased with the concentration of inhibitor but decreased proportionally with temperature. It appears that the steric hindrance of the aliphatic chain on the imidazoline ring adsorption may affect inhibitor efficiency. Polarization curves showed that the oleic imidazoline (OI) acted essentially as a mixed type inhibitor, in which the blocking of active sites occurred. As a result of film formation, impedance spectra revealed a considerable increase in the charge transfer resistance as indicated by the second capacitive loop. XPS depth profile analysis observed the presence of nitrogen and carbon species on the inhibitor film, which were associated to the OI. [source] Exfoliation corrosion of aluminum alloy AA7075 examined by electrochemical impedance spectroscopyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2004F.-H. Cao Abstract A typical aluminum alloy, AA7075, was immersed in the EXCO solution, and its corrosion properties during different immersion time were measured repetitively using electrochemical impedance spectroscopy technique (EIS). The EIS data a were simulated using equivalent circuit with ZView program. The results show that once the exfoliation occurs, the low frequency inductive loop in the Nyquist plot associated with the relaxation phenomenon of reaction intermediates disappears, and the Nyquist plane is mainly composed of two capacitive arcs in the high frequency range and low frequency range respectively. The former originates from the original corroded surface, while the latter from the newly formed interface by exfoliation corrosion (EXCO). With the increased immersion time, the high frequency capacitance arc decreases gradually, while the low frequency capacitance arc increases gradually. From the beginning of immersion up to 9 hours, charge transfer resistance gradually decreases, illustrating the acceleration of the corrosion rate, whereas the proton concentration decreases steeply, indicating the cathodic process is pre-dominant. Then the corrosion rate decreases gradually corresponding to the exhausting of proton ions. The results also show that the exfoliation corrosion is developed from pitting corrosion through intergranular corrosion to general corrosion at the end. [source] | ||||||||||