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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La 0.6 Sr 0.4 Fe 0.6 Mn 0.4 O 3−δ (LSFM) perovskite-type catalysts were prepared by a nanocasting route based on solution combustion synthesis, called the soft−hard templating (SHT) approach. Three silica hard templates with different textural properties were used to increase the specific surface area of the perovskites, and hence to improve their electrochemical activity for both oxygen evolution and reduction reactions. Careful structural and physicochemical characterization revealed that the materials are composites formed by crystalline LSFM perovskite and amorphous metal silicates, even after the etching procedure. Both the composites' specific surface area and the fraction of silicates are proportional to the silicas pore volume. Interestingly, the LSFM perovskite obtained by SHT has lower cell volumes than the parent oxide prepared without a silica template. The electrochemical characterization revealed the contrasting effects of the metal silicates on the performances of the electrodes. The LSFM-SHT-based electrodes have higher double-layer capacitance and higher current for oxygen evolution than those prepared with the parent LSFM. Furthermore, the LSFM-SHT-based electrodes show a preferential 4-electron pathway during the oxygen reduction reaction, if the amount of amorphous silicates is low (Si wt % < 3.5 wt %). However, the silicates also shift the onset potential of both oxygen evolution and reduction reactions to more positive and negative potential values, respectively, thus delaying the two reactions.

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PtRu/C-LaNiO 3 composite coatings on Ni foam supports were prepared by brush painting and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy analysis and cyclic voltammetry. The electrodes electrocatalytic properties toward the oxygen evolution reaction in alkaline medium were evaluated by steady state measurements. The results show that PtRu/C loading of 5% produce electrodes more active than the LaNiO 3 coating for the oxygen evolution reaction. The improved electrocatalytic performance of the composite electrodes was related to the increase of the exchange current density and the shift of the Tafel lines for less positive potentials compared to the LaNiO 3 oxide electrodes. The enhanced performance of the composite electrodes was attributable to enhancement of the electrical conductivity, higher surface area and to the electrocatalytic nature of the composite.Oxygen evolution reaction (OER) is one of the processes currently limiting the performance of Regenerative Fuel Cells (RFCs). The reaction exhibits severe electrochemical overpotential which lowers the energy efficiency of RFCs. Noble metals are still considered the best electrocatalysts for the oxygen reactions as they provide the lowest overpotential and highest stability. However the level of precious metal required for high activity and stability leads to high costs. Alternative materials such as mixed oxides are very interesting for catalytic applications and its combination with small amounts of precious metals could lead to improved electrode activity for OER due to synergistic effect between noble metal and oxide. 1-4 The perovskite oxide LaNiO 3 is among those considered for use as electrocatalyst and electrocatalyst support in RFC systems due to its metallic conductivity, reasonable stability and low cost. Recently it was proposed by Yuasa et al. the use of LaNiO 3 as a potential material to replace carbon black, owing to its higher stability against anodic polarization as compared to carbon support. 5 During the past years our efforts have been devoted to study coated electrodes, based on the perovskite-type oxide LaNiO 3 , in order to optimize their performance for the OER, via the use of an adequate oxide preparation method and the choice of Ni foam as support. [6][7][8][9] In order to improve the performance of these coated electrodes, the addition of PtRu nanoparticles supported on Carbon was attempted. In this work we present our results on the performance of PtRu/CLaNiO 3 composite coatings on Ni foam supports as anodes for OER in alkaline medium. The electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy analysis (EDS) and cyclic voltammetry (CV). Their electrocatalytic properties were evaluated by steady state measurements.The comparison with LaNiO 3 oxide coatings on Ni foam supports shows the manifested benefit of the addition of PtRu/C nanoparticles on the improvement of the composite electrode activity for the OER. ExperimentalThe perovskite-type oxi...