Oscillatory behaviour in Galvanostatic Formaldehyde Oxidation on Nanostructured Pt/Glassy Carbon Model Electrodes

Abstract

The electrocatalytic oxidation of formaldehyde, which results in CO(2) and HCOOH formation, was investigated under galvanostatic conditions on nanostructured Pt/glassy carbon (GC) electrodes fabricated by employing colloidal lithography (CL). The measurements were performed on structurally well-defined model electrodes of different Pt surface coverages under different applied currents (current densities) and at constant electrolyte transport in a thin-layer flow cell connected to a differential electrochemical mass spectrometry (DEMS) setup to monitor the dynamic response of the reaction selectivity under these conditions. Periodic oscillations of the electrode potential and the CO(2) formation rate appear not only for a continuous Pt film, but also for the nanostructured Pt/GC electrodes when a critical current density is exceeded. The critical current density for achieving regular oscillation patterns increased with decreasing Pt nanodisk density. Lower oscillation frequencies of the electrode potential and lower CO(2) formation rate for nanostructured Pt/GC electrodes compared to continuous Pt film at similar applied current densities suggest that transport processes play an essential role. Moreover, from the simple periodic response of the nanostructured electrodes it follows that all individual Pt disks in the array oscillate in synchrony. This result is discussed in terms of the different modes of spatial coupling present in the system: global coupling, migration coupling and mass transport of the essential chemical species, and the coverage of corresponding adsorbates.

Separate Current Range for Appearance of Potential Oscillation during Methanol Oxidation on Platinum

“…For the oxidation of formaldehyde, Miki et al 12 have proposed adsorbed bridge-bonded formate. Seidel et al 13 have shown that formic acid is produced in the direct path.…”

Temporal Instabilities in Anodic Oxidation of Small Molecules/Ions at Solid Electrodes

“…The interaction of . Reprinted from [19], Copyright 1995, with permission from Elsevier both Cl À and Br À is strongest for Pt(100), less pronounced for Pt (111), and weakest for Pt(110)-so weak that the oscillations were not detected. This sequence correlates with the oscillations which are only observed if anions adsorb so strongly that they lead to a decrease of the H 2 -oxidation current in the Cu-upd region in the Cu-free solutions.…”

“…In very recent studies of the formaldehyde oxidation, Seidel, Krischer et al [111] have applied the nanostructured Pt/glassy carbon model electrode. In other words, the electrode consisted of catalytically active Pt nanodisks supported onto a planar glassy carbon substrate (Fig.…”

“…In other words, in spite of its nanostructured nature, the whole electrode can be considered a single oscillator. In the interpretation of this synchronization a reasonable assumption was done that all the [111] oscillators face the same (bulk) concentration of formaldehyde, while the concentration of the formic acid at the electrode surface (and not present in the bulk) oscillates. It is considered that the coupling between different "nanooscillators" is not of transport (diffusional), but of electrical nature, which can include, e.g., migration effects.…”

Photo‐electrochemical Oxidation of Organic C1 Molecules over WO3 Films in Aqueous Electrolyte: Competition Between Water Oxidation and C1 Oxidation

“…[35,36,40,41] In these reactions, an increaseoft he Pt loading or the Pt nanodisk coverageo nt he glassy carbon substrate, or alternatively,adecrease of the flow rate, was found to result in ah igher CO 2 current efficiency. This was explainedb ya ni ncreasingp robability of re-adsorptiona nd furthero xidation of the incompletely oxidized reactioni ntermediates to the completely oxidized and stable product CO 2 .…”