Herein, sampled current voltammetry (SCV) is exploited to study the kinetics of electrochemical reactions with electrode materials that are unsuitable for rotating disc or microelectrode experiments. The approach described opens up the possibility of assessing the electrocatalytic activity of films produced by high throughput deposition techniques, especially conducting films formed on insulators. This is particularly valuable for testing novel oxygen reduction or oxygen evolution catalysts. SCV is a transient technique, yet for processes affected by mass transport, it produces sigmoidal current-voltage curves, which can be analyzed as conventional steady state voltammograms. Selecting different sampling times affords a range of mass transfer coefficients and this is particularly useful to determine kinetic parameters. The applicability of SCV is first assessed with the fast electron transfer between ferri and ferrocyanide ions and an excellent agreement between the SCV and RDE methods is found. Then, SCV is used to investigate the oxygen reduction reaction (ORR) on a stationary polycrystalline Pt disc, on a polycrystalline Pt foil and on a thin Pt film oriented in the (110) direction. The results are systematically compared with those from a rotated polycrystalline Pt disc. Importantly, the sampled current voltammograms (SCVs) are found to be sufficiently sensitive to reveal differences in electrocatalytic activity between the Pt electrodes and between different sulfate concentrations. The technique is thus well adapted to probing variations in catalytic activity due to surface structure or interactions between solution species and surface sites. For polycrystalline Pt, the ORR kinetic parameters obtained from the Koutecký-Levich (K-L) analysis of the SCVs are in good agreement with those obtained with the RDE. Overall, the sampled current voltammetry approach reported here provides a valuable alternative to steady state voltammetry, and it is particularly suited to assess the electrocatalytic properties of surfaces where epitaxial thin film electrodes are grown on insulating 3 substrates. The methodology could easily be extended to other substrates such as catalysts deposited on gas diffusion electrodes.
Nickel containing perovskite type oxides have been reported within the most active materials for OER in alkaline media and also with good electrocatalysts properties for OOR. The increase of the bifunctional character of these materials is the subject of research in view of the need for alternatives to noble materials and to the paramount importance of electrode development for the next generation of regenerative fuel cells. The LaNiO 3 oxide was prepared by a self-combustion method using citric acid. The electrodes were prepared by coating a nickel foam support with an oxide suspension. Electrochemical characterization was carried out by Cyclic Voltammetry (CV) and Electrochemical Impedance (EI). The electrode's roughness factor has been estimated from the charging currents (i c ) recorded between -0.050 V and +0.050 V (Fig 1-a). From the linear variation between the i c vs sweep rate (sr), the double layer capacitance of 0.208±0.015 µF cm -2 was calculated (Fig 1-b). EI spectra were fitted to an equivalent circuit that rendered capacity values in agreement with those estimated by CV.The oxide coating roughness factor was estimated as 3463±250, representing a much higher value than those reported in the literature [1,2] for the same oxide. This enhancement of the electrodes roughness can be associated with the oxide preparation method associated with the use of Ni foam as the oxide support.
AcknowledgementsThis work is partially financed by Fundação para a Ciência e Tecnologia (FCT), under contract nº PTDC/CTM/102545/2008.
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