Pattern formation during electrocatalytic reactions on Pt film-electrodes: An in situ, time-resolved, spatially two-dimensional infrared absorption spectroscopy study
Final Report Abstract
We studied self-organization phenomena occurring during the electrooxidation of CO on Pt electrodes in the presence and absence of strongly adsorbing anions, and during the electrooxidation of H2-CO mixtures on Pt both experimentally and theoretically. Experiments were performed with spatially resolved ATR-FTIR spectroscopy and with potential probe measurements. In the absence of halides (or other strongly adsorbing anions) the prevailing bifurcation in both the electrooxidation of CO and of H2-CO mixtures was the domain bifurcation which lead to scale-free CO-covered regions surrounded by reactive surface. Furthermore, from the absence of a red-shift of the CO vibrational band at apparently lower coverages we inferred that a sub-structuring of the domains into densely packed CO microislands occurred. In the H2 -CO-system the domains could also undergo a Hopf bifurcation leading to breathing islands. In the presence of halides, the reported particularly large parameter regions in which oscillations had been observed could be explained with a refined model taking into account an asymmetric inhibition of the adsorption of CO and OH by adsorbed anions. This model predicts oscillations that are solely driven by the reaction kinetics, thus not requiring any mass transport limitation or an IR-drop in the electrolyte or the outer electric circuit. Also pattern formation in this system was very rich, and a number of unusual patterns were observed, among them solitary waves with free and non-curling open ends, soliton-like pulse interactions, and backfiring. The latter two dynamical features could be reproduced with an effective 3-component model, taking into account the Langmuir-Hinshelwood mechanism of CO electrooxidation, anion adand desorption as well as the dynamics of the electrode potential. Furthermore, we could show that the alignment of pulses in flow direction as well as the existence of traveling solitary waves perpendicular to the flow is a results of advection in the experiments, which were carried out in a linear flow cell. Some of the features were investigated in a more general context with a prototypical reaction-diffusion-advection system.
Publications
- Spatially resolved ATR- FTIRS study of the formation of macroscopic domains and microislands during CO electrooxidation on Pt, ChemPhysChem 11 (2010) 3002
Philipp R. Bauer, Antoine Bonnefont and Katharina Krischer
- Mechanistic aspects of oscillations during CO electrooxidation on Pt in the presence of anions: Experiments and Simulations, Catalysis Today 202 (2013) 144
Sauradip Malkhandi, Philipp R. Bauer, Antoine Bonnefont and Katharina Krischer
- Selforganized patterns during the oxidation of H2 -CO mixtures on a rotating Pt ring-electrode, Electrochimica Acta 112 (2013) 894
Elizeth Ramirez-Alvarez, Ramiro Rico-Martinez and Katharina Krischer
