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The time-dependent hydrogen evolution reaction (HER) on Ni electrodes shows a large increase in electrode overpotential with time. This is ascribed to hydride formation at active Ni cathode surfaces. Hydride formation was detected by x-ray diffraction, morphological changes at the electrode surfaces, and resulting changes in secondary electron emissivities. Nickel electrodes annealed for 2 h in an argon atmosphere at 1000~ after HER did not show x-ray lines assigned to hydride. On the other hand, hard nickel electrodes (180 HV5/30) show high overvoltages as well as hydride x-ray diffraction lines after HER. By taking the variation of the nickel electronic density of state following hydrogen sorption into account, we are able to satisfactorily explain the increase in nickel overpotential after a few hours of HER.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 142.150.190.39 Downloaded on 2014-12-20 to IP

The charge-transfer reaction between copper͑II͒ and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H 2 SO 4 ϩ 0.3 M CuSO 4 ϩ chloride ions (c Cl р 1 ϫ 10 Ϫ2 M͒, and polyethyleneglycol 1500 ͑PEG, c PEG р 4 ϫ 10 Ϫ3 M͒. Electrochemical quartz crystal microbalance ͑EQCM͒ measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCl on the electrode surface at c Cl у 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCl deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl Ϫ surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu ϩ nor Cu ϩϩ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu͑II͒ support the proposed mechanisms, in particular the role of the intermediate Cu ϩ .

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Electrochemistry / Copper / Halides / Mechanism / Electroplating / ElectrorefiningThe cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2 M H 2 SO 4 + 0.3 M CuSO 4 ) is markedly affected by the presence of small concentrations of halide ions. Chloride ions accelerate the reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuCl and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3 M CuSO 4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.

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Continuum hydrodynamics and no‐slip boundary conditions apply to electrochemical quartz microbalances of the thickness shear mode type with gold in aqueous contact. Electrochemical phase‐stabilized quartz micro‐balance measurements can give insight into ion adsorption, solvation, hydrogen bonding, and water clustering at charged surfaces. Species in the outer and inner Helmholtz layer can be treated as rigidly coupled masses. Frequency changes on polycrystalline gold electrodes in alkaline aqueous contact, and in the potential range from the hydrogen evolution up to the bulk oxide formation, are primarily caused by ion solvation and ion pair formation. Specifically adsorbed anions, like sulfate and hydroxide, are stripped of nearly half of their original solvation shell, and function as counter charge carriers analogously to completely solvated anions in the outer Helmholtz plane. Their saturation coverage is limited by lateral electrostatic repulsion and steric crowding by their solvation shells. Specifically adsorbed anions which form neutral ion pairs with alkali metal cations practically do not exhibit electrostatic repulsion and solvation shell crowding. They contribute much stronger to the double layer loading than specifically adsorbed partially hydrated ions and non‐specifically attracted species. In the oxide monolayer potential region, electrosorbed hydroxyl functions are deprotonated, and become neutralized by alkali metal ions at high pH. In a first order approximation, viscous fluid coupling and roughness changes do not have to be invoked to explain the observed frequency data.

The frequency change of an electrochemical quartz crystal microbalance (EQMB) is a function of both the rigid and the viscous masses coupled to its surface. The viscoelastic properties of the contacting medium define the mechanical loss of the vibrating quartz, which is characterized by the resistance R' in the equivalent electrical circuit. A new driver circuit for the EQMB is described. It permits monitoring of in situ changes of the resonant frequency fs and of the quartz crystal equivalent resistance R'. Thus this set-up allows one to distinguish between the rigid and viscous masses. Results obtained in different media with a prototype are discussed.