Bistability and oscillations during electrooxidation of H₂-CO mixtures on Pt: Modeling and bifurcation analysis

A model describing the electrooxidation of H₂-CO mixtures on rotating Pt electrodes is presented together with a bifurcation analysis for the main experimental parameters. We discuss dynamic instabilities partly caused by a chemical autocatalysis stemming from the CO subsystem and partly from an electrical autocatalysis with the electrode potential as the essential positive feedback variable. Hence, the system contains two different pairs of activator-inhibitor feedback loops. Depending on the parameters, one of the two interaction schemes is dominant, and we find either a so-called S-NDR or an HN-NDR system. However, there are also parameter regimes where the interplay of both loops gives rise to oscillations, greatly enlarging the dynamically unstable parameter range.