Showing papers on "Overpotential published in 1979"

Cathodic and Anodic Polarization Phenomena at Platinum Electrodes with Doped CeO2 as Electrolyte I . Steady‐State Overpotential

Abstract: Electrode polarization is studied by means of a current interruption method with the aid of a reference electrode. In this way anodic and cathodic overpotentials, η, can be measured separately, and the electrolyte polarization (IR drop) can be distinguished from the electrode overpotentials. Platinum paste electrodes are used with several doped ceria electrolytes in oxygen‐argon gas atmospheres. At high , the curves obey the Butler‐Volmer equation, with transfer coefficients of unity, both for anodic and cathodic polarizations. This result implies a charge‐transfer (or activation) mechanism. Study of the exchange current, , as a function of and temperature shows that oxygen for the charge‐transfer process is supplied through adsorbed adatoms on the Pt electrode surface, obeying the Langmuir isotherm. An activation energy of 1.75 eV is obtained for the charge‐transfer step. At low , limiting‐current behavior is obtained for the cathodic polarization, characteristic of a concentration polarization. A scanning electron microscope study of the electrode structure helps to understand the deterioration of electrical properties which occurs when samples are subjected to high temperatures and/or current densities.

Semiconductor Electrodes XVI . The Characterization and Photoelectrochemical Behavior of n‐ and Electrodes in Acetonitrile Solutions

Abstract: The photoelectrochemical behavior of n‐type and p‐type is investigated in acetonitrile solutions containing various redox couples. The cyclic voltammograms of the semiconductor electrodes in the dark and illuminated with red light are compared to the Nernstian behavior at a Pt disk electrode. The photodissolution of the semiconductors was surpressed and did not occur until potentials well positive of the flatband potential. An underpotential (negative overpotential) was developed on the photoassisted oxidation (n‐type semiconductor) and reduction (p‐type material) of solution species. Intermediate levels or surface states are shown to be capable of mediating electron transfer and limiting the magnitude of the underpotential produced. It is also shown that the production of surface films at potentials negative of the conduction bandedge can produce a photovoltaic effect with the assisting in electron transfer. Thus, photoassisted electron transfer with electroactive solution species is observed spanning a potential range greater than 2.5V utilizing a 1.35 eV photon.

The zinc-chlorine battery: half-cell overpotential measurements

Abstract: The voltaic performance of the zinc-chlorine battery was investigated by measuring the individual potentials of the Zn and Cl2 electrodes versus a reference electrode. The overpotential at the Zn electrode is very small for both the charging and the discharging processes, and the use of a flow-through porous Cl2 electrode is advantageous. Energy efficiency in the region of 65% has been achieved for a complete cycle. Tafel polarization data for both the zinc and the Cl2/graphite electrodes was obtained using rotating zinc hemisphere and graphite disc electrodes. Exchange current densities and Tafel slopes are reported.

The critical overpotential for copper dendrite formation

Abstract: The difference between surface roughness amplification and dendritic growth in copper electrodeposition in the limiting current density range is shown. The critical overpotential of copper dendrite growth is determined as 550 mV.

On the electrodeposition of hard gold

Abstract: The electrodeposition of hard gold in layers of 2 μm was investigated. The electrolyte was an acid citrate bath (pH 3·5) with cobalt as an additive. A flow cell allowed a controlled variation of the hydrodynamic conditions. The following features were examined quantitatively in the experiments: the current efficiency for gold deposition (10–30%), the carbon and cobalt content, as well as the porosity of the deposits, and the morphology [by scanning electron microscope (SEM)]. Above 50 mA cm−2 the deposition of gold and to a minor extent the incorporation of cobalt become mass transport limited (with certain complications resulting from the complex nature of the diffusion layer). The influence observed below 50 mA cm−2 seems to be due to the synergic effect of the transport controlled reduction of dissolved oxygen. A simple qualitative model for the incorporation of carbon is proposed. The substantial decrease in current efficiency observed upon the addition of cobalt to the bath is probably causedboth by a decrease of the hydrogen overpotential and by an increase of the overpotential for gold deposition. From the viewpoint of technical application, the most relevant result, is the substantial decrease in porosity at decreasing current density (c.d.) and increasing flow rate.

The critical overpotential for zinc dendrite formation

Abstract: The critical overpotential for zinc dendrite growth is determined as 173 mV by the method described by Popovet al. [1]. It was shown that this procedure can be applied successfully to metal deposition processes when there is a large codeposition of hydrogen.

Mass-transport separator for alkaline nickel-zinc cells and cell

Abstract: A mass-transport separator for use in alkaline nickel-zinc cells which coises a barrier layer of a microporous membrane which contains a laminate of a material having a hydrogen overpotential in alkaline solution which is lower than that of zinc, the barrier layer being sandwiched between two protective layers of microporous polyolifin material.

The anodic dissolution of copper in a fluidized bed electrode

Abstract: The paper reports on the study of the anodic dissolution of copper particles forming a fluidized bed electrode in sulphuric acid solutions containing copper (II). The distribution of overpotential along the length of the fluidized bed electrode has been measured and the variation of the current efficiency for the dissolution was determined as a function of the current density and the fixed bed thickness. A comparison is made with earlier results for copper deposition in a fluidized bed electrode with the same characteristics.

Concentration Changes in Porous Zn Electrodes during Cycling

Abstract: Concentration changes that occur in porous zinc secondary electrodes during cycling were measured. Changes occurring within cycles are similar to those postulated in the convective flow theory of zinc secondary electrode shape change. The drastic cumulative changes in concentration as cycling progresses predicted by the theory were not observed in the cells studied. Overpotential measurements taken during cell operation were compared with values of concentration overpotential calculated on the basis of the observed concentration changes. Failure of the experimental overpotentials to correlate with the calculated values is discussed. 10 figures, 1 table.

Effect of codeposition of polymer on the morphology of electrodeposited copper

Abstract: Poly(4-vinyl pyridine-co-methyl methacrylate), which is soluble in water in its protonated form and insoluble as a neutral molecule, has been synthesized and introduced into an acid bath for copper deposition. Potential-sweep investigations have shown that the copolymer affects the electrocrystallization of copper on graphite by delaying nucleation even before conditions for codeposition of the polymer are reached. At overpotentials at which the diffusion limiting current of copper is reached and hydrogen evolution starts, alkalinity at the electrode surface causes precipitation of the polymer. This is found to affect the resistivity of the deposit. Electron microscopy revealed that under such conditions copper is deposited in the form of globular particles, the size of the globules being in the micron range and decreasing with increasing overpotential.