Behaviour Of Pt Electrodes Research Articles

Influence of experimental factors on the constant phase element behavior of Pt electrodes

Constant phase element is still an object of controversy in the literature. It replaces capacitance or pseudocapacitance at solid electrodes. In the present paper influence of experimental parameters as cell geometry, distance between the working electrode and the Luggin capillary, surface roughness, and adsorption on the CPE parameters was studied. The obtained results indicate that the main cause of such behavior is adsorption of trace impurities from solution.

Characterisation of the electrochemical redox behaviour of Pt electrodes by potentiodynamic electrochemical impedance spectroscopy

Multi-frequency ac responses of Pt in aqueous solutions of sulphuric and perchloric acids have been characterised in cycles of Pt oxide anodic formation and cathodic reduction as functions of electrode potential, using the two orders frequency range below 1 kHz, where the double layer responded jointly with Faradaic processes. The potentiodynamic impedance spectra were fitted to an equivalent circuit, which contained double-layer capacitance in parallel with charge transfer resistance, R, and constant phase element (CPE). Double-layer capacitance has shown minima (20–25 μF cm−2 in 0.5 M H2SO4 and 25–35 μF cm−2 in 1 M HClO4) in the double-layer region and more than twofold increase in the platinum oxidation region. R−1 and CPE have shown maxima in the regions of platinum oxidation and reduction. Potentiodynamic curves of raw impedance data were also self-descriptive in monitoring platinum oxidation and reduction in both solutions and in presence of chloride.

Characteristics of Nano-crystalline TiO2Dye-sensitized Solar Cells having Counter Electrodes with Different Preparing Process

The Pt counter electrode of a dye-sensitized solar cell (DSSC) plays a role in helping redox reaction of iodine ions in electrolyte, also, transferring electrons into electrolyte. In this case, it is expected that characteristics of Pt electrodes strongly depend on fabrication process and its surface condition. In this study, Pt electrodes were prepared by a electro-deposition and a RF magnetron sputtering. Electrochemical behavior of Pt electrodes was compared using cyclic-voltammetry and impedance spectroscopy. Surface morphology of Pt electrodes was investigated by FE-SEM and AFM. I-V characteristics of DSSC were measured and discussed in association with the surface properties of counter electrode. As a result, electrochemical properties of electro-deposited Pt electrode were superior to that of sputtered Pt electrode. This is likely that enlarged area of surface in electro-deposited Pt electrode in comparison with the case of sputtered Pt electrode playa role in enhancing such electrochemical properties.

Microstructure of Pt electrodes and its influence on the oxygen transfer kinetics

Electrode morphology plays a key role in establishing O 2/O 2- redox equilibrium at the Pt electrode/O 2- conducting solid electrolyte interface and is believed to be the major cause for the reported discrepancies in the mechanism of oxygen transfer reaction. The temperature and the gas composition to which these interfaces are exposed have a strong influence on the electrode microstructure. In this paper a systematic study of the effect of temperature, time of heat treatment, electrode thickness and gas composition on the microstructure and impedance behaviour of Pt electrodes has been made. The electrodes in the as deposited state have very high initial surface area, small crystallite size (70–100Å) and extensive three phase contract boundary. The crystallite size after heat treatment at 600°C was < 0.1 μm but it increased to >1.0 μm after the 900°C heating. The sintering and grain growth of Pt particles led to increases in the time constant and the electrode resistance. The relationship between microstructure and the electrode behaviour is intricate. The electrode arcs in the impedance plane were invariably skewed, dispersed and in some cases two arcs were clearly separated. The optimum electrode thickness is a function of maximum temperature, time and gas composition to which the electrodes are exposed.

Electrical stimulation with Pt electrodes. IV. Factors influencing Pt dissolution in inorganic saline

Trace analysis has shown that Pt electrodes can suffer appreciable dissolution when used to apply biphasic current pulses of the type used in neural stimulation. The dissolution occurs even under conditions where other irreversible faradaic reactions e.g., H 2O electrolysis, are avoided. In the present study, factors influencing the dissolution of Pt electrodes during biphasic pulsing in neutral inorganic saline have been examined. The findings are consistent with the behaviour of Pt electrodes reported in other inorganic media. In a given test, the quantity of Pt dissolved was found to be a linear function of the aggregate anodic or cathodic charge injected. Therefore, dissolution ‘rates’ can be conveniently expressed in terms of nanograms of Pt per coulomb injected e.g., 100 ng C −1. Most of the Pt went into solution as Pt (II) species, so the above rate would correspond approximately to 100 p.p.m. of the anodic charge per pulse. For anodic-first (AF) pulses, charge density was the major factor controlling dissolution, whereas for cathodic-first (CF) pulses, pulse duration had the greater influence. Depending on the polarity (AF or CF), charge density, and duration of the biphasic pulse, the dissolution rate for smooth bead electrodes ranged from 30 to 300 ng C −1. Lower rates were achieved with platinized electrodes but in the absence of organic solutes, it is unlikely that Pt dissolution can be completely suppressed.

Electrical stimulation with Pt electrodes. V. The effect of protein on Pt dissolution

The effect of protein on the charge-induced dissolution of Pt stimulation electrodes was studied in an in vitro system. Biphasic pulses (± 400 mA, ± 400 μmCcm −2 geom.) were applied to smooth Pt bead electrodes (surface area = 0.03−0.08 cm 2) in a buffered saline solution containing 0.075–0.2 mg/ml human serum albumin; pulse solutions were analysed periodically for dissolved Pt by flameless atomic absorption spectrometry. The incorporation of protein in the pulse solution drastically altered the dissolution behaviour of Pt electrodes. Whereas dissolution in organic saline solutions proceeded essentially in a linear fashion, the rate in protein solution decreased with time and asymptotically approached zero. The passage of electric charge was required for the observed inhibition to develop but was not required to maintain it. In contrast, the constant presence of at least 0.15 mg/ml protein in the pulse solution was required for inhibition to develop and continue. Higher concentrations of protein did not enhance the observed inhibition. These findings bear favourably on the prospect for in vivo use of Pt stimulation electrodes: the dissolution process now appears to place no greater restriction on the acceptable pulse parameters than do other irreversible reactions such as H 2O electrolysis.

Anodic behavior of platinum electrodes in oxygen-saturated acid solutions

The anodic behavior of Pt electrodes in O 2-saturated sulfuric acid solution is shown to be critically dependent on the treatment of the electrode. The open circuit potentials, 1.48, 1.13 and 0.98 V, observed in purified solution, are related to the thermodynamic platinum-oxide potentials. The erratic behavior of Pt electrodes in non-purified solutions is also explained. The thermodynamic value of 1.23 V for the H 2O-O 2 reaction was obtained when certain conditions were fulfilled. The Tafel (b) parameter for the anodic oxygen evolution reaction was o.113, and i o = 2.5 × 10 −10 A/cm 2. Chemisorption of oxygen leads to a dipole potential of 0.98 V. An oxide film is produced by anodic oxidation. This was confirmed by an optical method (thin film ellipsometer) which showed that the growth of a film commences only above 1 V. Cathodic transient technique was used to measure the oxygen coverage ( Q) of the Pt electrode as a function of the applied potentiostatic voltage ( V). A linear relationship between Q and V was found. This relationship, Q = f( V), is explained on the basis of a modified Cabrera-Mott model. The evidence suggests that growth takes place on certain sites of the first layer only.