Carbon electrochemical measurements

N.R. Ferreira, A. Ledo, J.G. Frade, G.A. Gerhardt, J. Laranjinha, and R.M. Barbosa, Electrochemical measurement of endogenously produced nitric oxide in brain slices using Nafion/o-phenylenediamine modified carbon fiber microelectrodes. Anal. Chim. Acta 535, 1—7 (2005). 

Figure 5.17 Reversible amount of hydrogen (electrochemical measurement at 298 K) versus the BET surface area (circles) of a few carbon nanotube samples including two measurements on high surface area graphite (HSAC) samples...

The actual drive can be of the belt type (indirect) or axial (direct). While the former puts less stress on the rotating parts, the second is simpler and is very often used nowadays. Eccentricity of rotation must be minimised nevertheless, a slight eccentricity will not affect the electrochemical measurements so long as solution which has reached the electrode does not then pass over it again [132,133]. Electrical contacts with the external electronics can be of the silver—carbon brush type or enclosed mercury. A problem with the former is that particles from the brushes can contaminate the solution if proper care is not taken and, additionally, they give quite a lot of electrical noise at low rotation speeds mercury is to be preferred in these instances (up to about 50 Hz). At higher rotation speeds, noise from mercury contacts increases considerably and silver—carbon brushes have to be used. 

Two different reference electrodes are commonly used for electrochemical measurements in molten carbonates the oxygen electrode and the carbon monoxide electrode. 

Our study of the kinetics of the reaction of carbon with steam (152) was conducted by the circulation flow method under atmospheric pressure in the temperature-range of 900-1000°C. Dilution with helium was employed to vary the sum of partial pressures of the reaction participants. The experiments were carried out with nonporous graphite of high purity (the content of admixtures did not exceed 10"5%). The roughness factor of graphite was found to be 2-2.5 (from electrochemical measurements). Equation (390) proved not to be obeyed quantitatively the results of the variation of PHl in a broad range by addition of H2 to the gas mixture at the inlet do not form a straight line in the plot 1/r11 vs. PH2 ... 

D.D. Kindler, C. Thiffault, N.J. Solenski, J. Dennis, V. Kostecki, R. Jenkins, P.M. Keeney and J.P.Rr. Bennett, Neurotoxic nitric oxide rapidly depolarizes and permeabilizes mitochondria by dynamically opening the mitochondrial transition pore, Mol. Cell. Neurosci., 23 (2003) 559-573. N.R. Ferreira, A. Ledo, J.G. Frade, G.A. Gerhardt, J. Laranjinha and R.M. Barbosa, Electrochemical measurement of endogenously produced nitric oxide in brain slices using Nafion/o-phenylenediamine modified carbon fiber microelectrodes, Anal. Chim. Acta, 535 (2005) 1-7. 

Electrochemical measurement on carbon screen-printed electrodes... 

Although hydronium ion (H30+) (Chapter 8) and dioxygen (02) (Chapter 9) are the most studied of the molecules and ions without metal atoms, several of the molecules that contain sulfur, nitrogen, or carbon also are electroactive. The results for representative examples are presented to illustrate the utility of electrochemical measurements for die evaluation of the redox thermodynamics and bond energies for non-metal-containing molecules. In particular, die electrochemistry for several sulfur compounds [S8, S02, HS(CH2)3SH], nitrogen compounds [-NO, HON=0, N20, H2NOH, hydrazines (/ NHNH/ ), amines, phenazine], and carbon compounds (C02, CO, NCT) is summarized and interpreted. 

In summary, the electrochemical oxidation-reduction of organic molecules usually is mediated by the water (H20/H30+/H0 ) in the solvent matrix, especially if the substrate is more nucleophilic or electrophilic than water. Many reductions are catalyzed hydrogenations, and many oxidations are facilitated dehydrogenations. For these reasons, meaningful electrochemical measurements depend on the use of an inert electrode surface (not Pt, Pd, Au, or any other metal highly polished glassy carbon is the preferred choice in most cases). 

The goal of this volume is to provide (1) an introduction to the basic principles of electrochemistry (Chapter 1), potentiometry (Chapter 2), voltammetry (Chapter 3), and electrochemical titrations (Chapter 4) (2) a practical, up-to-date summary of indicator electrodes (Chapter 5), electrochemical cells and instrumentation (Chapter 6), and solvents and electrolytes (Chapter 7) and (3) illustrative examples of molecular characterization (via electrochemical measurements) of hydronium ion, Br0nsted acids, and H2 (Chapter 8) dioxygen species (02, OJ/HOO-, HOOH) and H20/H0 (Chapter 9) metals, metal compounds, and metal complexes (Chapter 10) nonmetals (Chapter 11) carbon compounds (Chapter 12) and organometallic compounds and metallopor-phyrins (Chapter 13). The later chapters contain specific characterizations of representative molecules within a class, which we hope will reduce the barriers of unfamiliarity and encourage the reader to make use of electrochemistry for related chemical systems. 

Electrochemical measurements can be readily adapted for on-line monitoring. An electrochemical detector uses the electrochemical properties of target analytes for their determination in a flowing stream. An electrochemical flow system, based on an SWV operation at a carbon-fiber-based detector, for use in the on-line continuous monitoring of trace TNT in marine environments was developed [16]. Such flow detector offers selective measurements of sub-part-per-million concentrations of TNT in untreated natural water samples with a detection limit of 25ppb. It responds rapidly to sudden changes in the TNT concentration with no apparent carryover. About 600 runs can be made every hour with high reproducibility and stability (e.g., relative standard deviation (RSD) = 2.3%, n = 40). The system lends itself to full automation and to possible deployment onto various stationary mobile platforms (e.g., buoys and underwater vehicles). 

It turned out that the admixture of sp2-carbon exerts a decisive effect on the electrode quality of diamond films. And yet, modern physical and optical experimental techniques, like Raman and Auger spectroscopy, AFM, etc., failed in the elucidation of subtle effects exerted by the admixture of non-diamond carbon on the behavior of polycrystalline diamond films it is the electrochemical measurements that give plausible information [22] (see Section 6.3). 

A CH Instruments 800B electrochemical analyzer (Austin, TX) was used for all electrochemical measurements and electrode preparation. Glassy carbon (GC) electrodes (3 mm diameter, geometrical area 0.07 cm2) were purchased from CH Instruments (Austin, TX) and polished with polishing alumina solution (BAS, West Lafayette, IN). All electrochemical measurements were conducted in a conventional three-electrode cell using Ag/AgCl (3M KC1) (CH Instruments,... 

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