Sampled current voltammetry for kinetic studies on materials unsuitable for rotating discs or microelectrodes: application to the oxygen reduction reaction in acidic medium

Abstract

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 analysed 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 orientated 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 substrates. The methodology could easily be extended to other substrates such as catalysts deposited on gas diffusion electrodes.

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