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 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.

Au(001) Thin Films: Impact of Structure and Mosaicity on the Oxygen Reduction Reaction in Alkaline Medium

“…More details about the application of the SCV to study the ORR can be found elsewhere. 62 The reconstructed sampled current voltammograms (SCVs) of the epitaxially grown Au(001) films recorded in 1.0 M KOH are shown in Figure 7A. For comparison, the SCV of a polycrystalline gold foil is also shown.…”

“…In previous work, we presented the SCV as an alternative method to study the ORR, and we demonstrated that, under appropriate experimental conditions, a good correspondence of the results obtained with SCV and the RDE could be attained. 62 ■ EXPERIMENTAL SECTION Thin Film Deposition. Au thin films were grown by PLD performed in a custom-made stainless-steel vacuum chamber equipped with a turbopump.…”

“…Before the experiments, all glassware were soaked in the acidic permanganate solution overnight, then immersed in the diluted piranha solution, and boiled in ultrapure water several times prior to use. The electrochemical cell used was a onecompartment electrochemical cell designed especially for the study of oriented thin films, 62 and a gold coil was used as a counter electrode. Two different reference electrodes were used: a mercury−mercury sulfate electrode (MMSE, saturated K 2 SO 4 ) for studies in acidic media and a mercury−mercury oxide (MMO, 20% KOH) for studies in alkaline media (both from Koslow Scientific Company).…”

Chemical and Electrochemical Pre-Treatment of Polycrystalline Platinum Electrodes and Interfering Substances Analysis

“…De acordo com adaptações realizadas no procedimento descrito por Soares et al, 26 todas as vidrarias e eletrodos foram imersos em solução de KMnO 4 1% por 12h e enxaguados com água ultrapura. Em seguida, realizou-se uma etapa de lavagem com peróxido de hidrogênio acidificado e lavou-se com água ultrapura todos os itens.…”

“…Após o banho na solução oxidante e os sucessivos enxágues com água ultrapura, foi utilizada uma etapa de lavagem com H 2 O 2 acidificada e posteriores enxágues com água ultrapura para que impurezas provenientes da solução de KMnO 4 fossem eliminadas do sistema reacional. O uso da solução de peróxido de hidrogênio acidificado (solução piranha) após o banho em KMnO 4 é descrito por Soares et al 26 como uma das etapas de limpeza de vidrarias.…”