Showing papers on "Electrode potential published in 1987"

Hydrogen ion selective microelectrode prepared by modifying an electrode with polymers

Abstract: Donnees sur un detecteur potentiometrique de pH, constitue d'une electrode de graphite recouverte d'un film de poly(pyrenamine) et d'un film de ionophore neutre, utilisant un echangeur d'ions hydrogene

Feasibility studies for the detection of organic surface and subsurface water contaminants by surface-enhanced Raman spectroscopy on silver electrodes

Abstract: Fundamental components of various families of organic contaminants that are found in surface and subsurface waters have been investigated by surface-enhanced Raman spectroscopy (SERS). The SERS substrate was a silver electrode maintained at various electrode potentials. The limit of detection for pyridine was calculated to be 8.5 pg. Variation of the electrode potential and excitation wavelength was used to qualitatively determine a two-component mixture of contaminants. The in situ type of conditions of low ionic strengths and humic materials was found not to inhibit the SERS effect on the silver electrode.

Adiabaticity of electron transfer at an electrode

Abstract: A simple description of the kinetics of electron transfer at an electrode is developed which includes the effects of both outer-sphere solvent dielectric relaxation and electron tunneling. From this description, an adiabaticity criterion is obtained which determines when the rate of the electron transfer is adiabatic, that is, determined by solvent relaxation dynamics, or diabatic, determined by electron tunneling dynamics. Rate constants are also obtained for the diabatic and adiabatic limiting cases and the intermediate regime in which the dynamics of both processes are important. The degree of localization of the electron transfer and the dependence of the rate on the electrode potential, the Miller indices of the electrode surface, the surface site of the reacting ion, and the distance of the ion from the electrode are examined. Possible extensions of the formalism to include other important factors are also discussed.

In situ surface extended x-ray absorption fine structure spectroscopy of a lead monolayer at a silver(111) electrode/electrolyte interface

Abstract: With use of fluorescence detection and grazing incidence excitation, the X-ray absorption spectrum was obtained, at the PbL/sub III/ edge, of a monoatomic adlayer of lead on a silver (111) electrode immersed in solution. The adlayer was produced by under potential deposition from aqueous lead acetate/sodium acetate electrolyte. The edge position and the near-edge structure confirm that the lead is fully reduced to the zerovalent state. The extended X-ray absorption fine structure (EXAFS) contains no detectable contribution from lead-silver scattering, either because the lead layer is incommensurate with the underlying silver lattice or because there is large thermal motion of the lead atoms. Instead, the fine structure is due to scattering from a single type of light atom, most likely oxygen. This oxygen must arise from adsorbed water molecules or acetate ions. The lead-oxygen distance changes with the electrode potential from 2.33 +/- 0.02 A at -0.53 V to 2.38 +/- 0.02 A at -1 V (vs. Ag/AgCl, 3 M KCl).

Effect of Electrode Potential on the Hydrogen-Induced IGSCC of Alloy 600 in an Aqueous Solution at 350 C

Abstract: Slow strain rate tests (SSRTs) were conducted to study the effect of electrode potential on the intergranular stress corrosion cracking (IGSCC) of Alloy 600 in deaerated 0.01 M H3BO3 + 0.0...

Electrooxidation of methanol on iridium in acidic solutions: electrocatalysis and surface characterization by infrared spectroscopy

Abstract: Electrooxidation of methanol was studied on iridium in H/sub 2/SO/sub 4/ and CHlO/sub 4/ solutions in connection with catalytic activities of the electrode in various oxidation states and of the adsorbed CO observed by infrared spectrometry. Iridium was found to show higher catalytic activity than platinum at low positive potential regions. The catalytic activity of iridium decreased with time at a constant-potential polarization and was inhibited by the introduction of CO gas. In situ infrared spectra were observed in the measurement conditions of electrode potential modulation and of constant electrode potential. The spectra for the above different conditions agreed in the wavenumber region of the spectra but not in absorbance intensity or in its relative values at different electrode potentials. The spectral maxima of the adsorbed CO, derived from methanol, were 2045 cm/sup -1/ at 0.2 V (vs. RHE) and 2054 cm/sup -1/ at 0.5 V. These maxima were shifted 20 cm/sup -1/ to higher wavenumber by the addition of CO gas. The catalytic activity of iridium was discussed in relation to redox coupling of iridium species in different oxidation states, the rate of their redox coupling, and the adsorbed CO observed by infrared spectroscopy.

A novel amperometric ammonia sensor.

Abstract: A novel amperometric ammonia sensor was designed in which an amperometric ammonium-ion selective polyvinyl chloride)-nitrobenzene gel electrode containing dibenzo- 18-crown-6 was covered with a gas-permeable membrane. This sensor gave a current response proportional to the ammonia concentration in the range from 2 to 200μmol dm-3. We examined the dependence of the current response on electrode potential, thickness of the internal- solution layer, and pH of the sample solution. The results were well explained by theoretical equations.

Performance characteristics and regeneration of a tetraphenylboron(III) selective electrode

Abstract: A tetraphenylboron (TPB)-ion-selective poly(vinyl chloride)-membrane electrode based on an ion pair complex of TPB/sup -/ with hexadecylpyridinium cation (HDP/sup +/) was prepared with dioctyl phthalate as a plasticizer. Effects of changing the ion pair percent in the membrane and pH of the test solution on the electrode potential were studied. It was found that soaking the electrode in HDP solution gives better response characteristics than those obtained from electrodes soaking in TPB solution. A method for regeneration of the exhausted electrode was proposed. The electrode was highly selective for TPB with respect to some amino acids and organic and inorganic anions. TPB was determined successfully by potentiometric titration with standard HDP solution when using the investigated electrode as the sensor.

Behaviour of surface intermediate states in anodic O2 evolution electrocatalysis at Co3O4 on Ni and Ti substrates

Abstract: Determination of the behaviour of the adsorbed species that are the kinetically-involved intermediates in multi-step Faradaic reactions of the electrocatalytic type has remained an undeveloped area of electrode kinetics, yet is important in the evaluation of electrocatalysis and reaction mechanisms of electrode processes as a function of current-density (i) and electrode potential (V). — From values of the complementary derivatives dV/d log i, AV(t)/d log t and dV(t)/d log [—dV(t)/dt], obtained from potential-relaxation measurements, the electrochemical behaviour and change of steady-state coverage with potential of the intermediate states in the OER at Co3O4 is derived. The behaviour observed is related to changes of oxidation state of the bulk oxide and its surface region. — The observed potential-relaxation and a.c. impedance behaviour is different at Co3O4 on Ni and Ti substrates. It is clearly shown that this effect arises from the additional component of impedance at the interface which is introduced by the presence of a thin underlying oxide film of TiO2 on the Ti, on which the Co3O4 film is formed. These observations have practical interest regarding preparation of composite electrocatalytic surface films on Ti substrates. Over most of the potential range studied, however, the mechanism and electrode kinetic characteristics of the OER are the same for the two metal substrates. — The O2 evolution kinetics and associated potential-relaxation behaviour on open-circuit, following current interruption, are determined by two pseudo-capacitances: one arising from the potential-dependent state of oxidation of metal ions in the oxide film and a second, coupled contribution from the potential-dependence of coverage by OH/O intermediates on the oxide film.

Rotating-disc electrodes. ECE and DISP1 processes

Abstract: Theory is presented for the shape of current–voltage curves measured at a rotating-disc electrode for the cases where the substrate reacts via either an ECE or a DISP 1 process in which the kinetic step is sufficiently fast to allow the use of the reaction-layer concept in the theoretical treatment. When the electrode potential for the electrode reaction can be found under conditions where there are no complications of coupled kinetics, analysis of the shift in half-wave potential with disc rotation speed allows the deduction of the rate constant for the kinetics of the homogeneous chemical process involved in each mechanism. If an independent measurement of this rate constant is available (e.g. from spectroelectrochemistry) then discrimination between ECE and DISP1 pathways is possible. Experiments involving the reduction of fluorescein in aqueous carbonate/bicarbonate buffers were found to be in good agreement with theory. Furthermore, comparison of the kinetic data with transient electrochemical e.s.r. data revealed the reaction mechanism to be DISP1, in agreement with previous observations.