Spatially Resolved ATR‐FTIRS Study of the Formation of Macroscopic Domains and Microislands during CO Electrooxidation on Pt

Abstract

Electrooxidation of CO in CO-saturated sulfuric acid electrolyte solutions with controlled mass transport is investigated with spatially resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy under galvanostatic and potentiostatic conditions. The reaction conditions are chosen such that steady states with intermediate current densities and intermediate average CO coverages are accessible. We demonstrate that under these conditions the reaction never proceeds uniformly on the electrode surface. Instead, macroscopic domains form spontaneously, composed of areas with high CO coverage and areas essentially free of adsorbed CO molecules. The average coverage within the CO-covered domains depends on the electrolyte concentration and the applied potential and can vary between saturation coverage and a few tenths of a monolayer. However, the absence of a red-shift of the CO vibrational band points to a further substructuring of the domains in densely packed CO microislands. These microislands most likely also form in the boundary layer between the CO-rich and CO-free electrode domains. This hierarchical patterning of the electrode surface is attributed to the interplay of autocatalytic reaction steps, spatial coupling through migration or the galvanostatic control of the experiment, and molecular interactions between molecules co-adsorbed on the electrode surface.

Experimental Assessment of the Sensitiveness of an Electrochemical Oscillator towards Chemical Perturbations

“…For example, surface heterogeneity is an important parameter in electrochemistry, particularly for polycrystalline electrodes, and may constitute the second degree of freedom necessary for complex oscillations to arise. In fact, it has been shown that even considerably simple reactions such as that for CO may display complex spatial distribution [63] and that electrochemical oscillatory reactions can possess a component in space [64]. Thus TFMSA could be acting on this parameter inhibiting specific sites by adsorption.…”

Dissipative solitons and backfiring in the electrooxidation of CO on Pt

“…We employed spatially resolved attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy 28 29 (also known as surface enhanced IR absorption spectroscopy, SEIRAS) to monitor the CO coverage in-situ in a flow cell as shown in Fig. 4 in the methods section below, where also experimental details are given.…”

Cooperative Behaviour of Pt Microelectrodes during CO Bulk Electrooxidation

“…[7] When stationary domains are formed, the S-NDR cannot be observed since the electrode potential value is nearly independent of the applied current and lies in the middle of the bistable region. [9,12,14] The observation of the S-NDR herein indicates that the diameter of the Pt microelectrodes is below the critical size required for pattern formation under the applied experimental conditions.…”

“…Rather, when trying to adjust an intermediate current density, self-organized spatial patterns form spontaneously, such as CO-covered domains under galvanostatic control, [8,9] or Turing-type patterns under potentiostatic control and low electrolyte conductivity. [10,11,12] In the following, we show that the S-NDR current branch becomes accessible when the size of the electrode is sufficiently reduced, more precisely when the reaction proceeds on a single 9 mm diameter Pt microelectrode. Furthermore, coupling of several Pt microelectrodes leads to the emergence of new cooperative behaviour consisting of their sequential activation when the applied current is increased.…”