The (100) crystallographic plane is the most active facet of iridium dioxide (IrO 2 ) for the oxygen evolution reaction (OER). Pulsed laser deposition was used to grow (100) IrO 2 on a (100) SrTiO 3 substrate at deposition temperature ranging from room temperature to 600 °C. Detailed structural and morphological characterization was performed using AFM, XRD, and X-ray reciprocal space mapping (RSM) to unravel the geometrical arrangement of [IrO 6 ] octahedra in the (100) IrO 2 thin films. It is shown that the symmetry mismatch between the substrate and the epitaxial thin film imposed an orthorhombic distortion of the tetragonal structure of IrO 2 and, as a consequence, the [IrO 6 ] geometry is distorted. These data were correlated to the OER characteristics established from electrochemical measurements. DFT modeling was employed to relate differences in surface relaxation of IrO 2 films prepared at different temperatures with changes in OER activity. Vacancy formation leads to higher surface stability at temperatures around 500 °C, which corresponds to the deposition temperature at which the electrocatalytic activity of (100) epitaxial IrO 2 film is maximal.

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Common in myopia and aging, vitreous opacities arise from clumped collagen fibers within the vitreous body that cast shadows on the retina, appearing as ‘floaters’ to the patient. Vitreous opacities...

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.

on a substrate by deposition methods allowing a fine control of film quality and thickness. [1][2][3] When talking about MSC, the total thickness of the stacked films is below 50 µm (substrate ≈ 500 µm) and the footprint surface (<1 cm 2 ) is controlled by etching technique (top down approach: chemical or plasma etching methods) or localized growth of the active material on current collector (bottom up approach: ink jet printing, electrodeposition).The first MSC was made in 2001 by Yoon et al.: the magnetron sputtering deposition technique was selected to stack electrode material and solid electrolyte on a silicon wafer giving rise to Si/SiO 2 /RuO 2 / LiPON/RuO 2 stacked layers. [4,5] The capacitance retention of this MSC was restricted (<1000 cycles) and the rate capability was limited owing to the low ionic conductivity of the LIPON solid electrolyte [6][7][8] (σ ionic ≈ 10 −6 S cm −1 at room temperature) but the triangular shape of the galvanostatic charge-discharge plot confirmed the pseudocapacitive properties of the RuO 2 /LIPON/RuO 2 MSC. More than 20 years after this first demonstration, it must be said that Vanadium nitride film made using a thin film deposition technique is a promising electrode material for micro-supercapacitor applications owing to its high electrical conductivity and high volumetric and surface capacitance values in aqueous electrolyte. Nevertheless, the cycling stability has to be improved to deliver good capacitance during a large number of cycles. Here, it is shown that vanadium nitride films made by a magnetron sputtering deposition method exhibit remarkable cycling stability (high capacitance retention value after 150 000 cycles), ultra-high rate capability (75% of the initial capacitance at 1.6 V s −1 ), while providing high surface capacitance values (≈1.4 F cm −2 ) and very low ageing of the VN electrodes (no loss of performance after 13 months). Additionally, new findings regarding the location of vanadium oxides species responsible for the charge storage mechanism in pseudocapacitive VN films are revealed by transmission electron microscopy electron energy-loss spectroscopy analyses at the nanoscale.

The next generation of Internet of Things devices requires micro-supercapacitors operating at high voltage which is difficult to achieve using symmetrical design. Thus, their fabrication in an asymmetric configuration is mandatory. While MnO2 is well-established as positive electrode, the scarcity of existing efficient materials able to be used at the negative side drives the research towards new promising materials. Since few years, a new class of oxide materials, named multicationic oxides, were demonstrated to be attractive solutions as bulk electrodes for electrochemical capacitor. Among them, the wolframite-type FeWO4 oxide was proposed as an interesting negative electrode material for asymmetric FeWO4/MnO2 electrochemical capacitors. The present paper reports for the first time on the successful thin film synthesis of such iron-tungstate oxide films by reactive DC magnetron sputtering, a deposition method widely used in the semiconductor industry to manufacture micro-devices. The pseudocapacitive behaviour documented at the bulk scale is preserved at the thin film level as well, and opens-up the possibility to use FeWO4 in the next generations of micro-supercapacitors.