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Changes in the voltammetric response of polycrystalline platinum in the direction expected for preferred oriented surface electrodes are achieved after applying a fast repetitive square wave potential signal covering the potential range of H-and O-electroadsorption/electrodesorption. The influence of the characteristics of the square wave potential signal on the voltammetric response of the modified platinum surfaces is systematically studied to establish the optimal conditions for obtaining surface structures with determined preferred orientations.Recently, it was found that changes in the voltammetric response of polycrystalline platinum electrodes in the direction expected for preferred oriented surface electrodes can be achieved by using a fast repetitive square wave potential signal (RSWPS) within the potential range of H-and O-electroadsorption/electrodesorption in acid solution (1). Similar results were earlier obtained by applying a fast triangular potential signal to a polycrystalline platinum electrode in acid electrolyte at room temperature (2, 3). After applying the fast potential perturbation the electroae surface modifications were voltammetrically followed at a low potential sweep rate in the H-and O-electroadsorption/electrodesorption potential range by using an acid electrolyte. These changes in the electrode surface can also be seen through SEM for a relatively low magnification factor (4). The change from the initial polycrystalline platinum surface to the preferred oriented surface is independent of the shape of the periodic potential perturbation, but it is extremely sensitive to its frequency and potential limits (1, 2, 5). Thus, depending on the preset parameters of the potential perturbation either the platinum (100) preferred oriented surface or the platinum (111) preferred oriented surface are obtained (1-5).In the present work the influence of the RSWPS characteristics on the voltammetric response at low potential sweep rate of the resulting platinum surfaces is systematically studied to establish the optimal conditions for obtaining surface structures with a determined preferred orientation. ExperimentalRuns were made in 1M H2SO4 at 25~ with commercially available polycrystalline platinum wire shaped working electrodes of ca. 0.10 cm 2 geometric area. Previous to each experiment the working electrode was electropolished with ac (50 Hz; 10-15V) in a slightly acid (HC1) saturated CaC12 solution. Later, the electrode was repeatedly rinsed with triply distilled water and kept in water for lh before use. The potential of the working electrode was measured against a RHE in the acid electrolyte. A large area platinum counterelectrode (ca. 50 cm 2) concentrically surrounding the working electrode was used. The electrochemical cell and the instrumentation have been described elsewhere (1, 5). The distortion of the RSWPS, which was due to the proper risetime of the electrochemical setup, was less than 5% at frequencies lower than 6 kHz.After the pretreatment, the working electrode was subjected ...

Pd oxide layers were grown by applying to smooth Pd electrodes a potential reversal technique (PRT) in 1 M H2SO4 at 25°C. The electroreduction of the Pd oxide layer was made either voltammetrically or potentiostatically, yielding a Pd overlayer with a large increase in surface area. The effective range of PRT conditions for increasing the Pd surface area was established. The increase in surface area of treated Pd was voltammetrically determined. The electrochemical behavior of treated Pd electrodes in acid revealed an enhancement of the H atom surface electroadsorption processes. This behavior is consistent with the fractal characteristics of the treated Pd electrode surface, as demonstrated by the analysis of scanning force microscopy imaging data.

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Oxygen evolution reaction (o.e.r.) kinetics in NaOH solutions have been studied on both fresh and oxide covered CosoNi2sSilsB10 amorphous alloy (G-16) electrodes. Steady state polarization curves obtained in different aqueous xM NaOH (0.1 ~< x ~< 4) in the 30-80 ° C range fulfill Tafel relationships at low overpotentials; the Tafel slope is close to 2.3(RT/F)V dec -~ for both G-16 and oxide coated G-16 electrodes. At high overpotentials, ohmic relationships with slopes becoming increasingly steep, regardless of the NaOH concentration, are observed. In the Tafel region, the reaction order with respect to OH-is near 2. The apparent current density at constant potential, for oxide coated G-16 electrodes, is greater than that for uncoated G-16. The high catalytic activity of the oxide coated G-16 for the o.e.r, is attributed to its spinel-type structure. The kinetics of the o.e.r, at low overpotentials is explained through a mechanism involving a first electron transfer step followed by a ratedetermining chemical step.

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The mechanisms of oxygen and hydrogen evolution on amorphous alloys G14 (Fe60C020SiloBlo) and G16 (CosONi2,Si,,Bl0) in 1 M KOH at T = 298 K and 333 K were studied by electrochemical impedance spectroscopy (EIS). Comparative measurements were carried out on polycrystalline Pt electrodes. Impedance spectra in the frequency range Hz I f 5 lo4 Hz were analyzed to determine the kinetic behaviour of amorphous alloys by application of transfer function analysis, using non-linear fit routines. The EIS-data are interpreted in terms of consecutive reaction mechanisms for both oxygen and hydrogen evolution.