NSC Seminar ’’Electrochemical Systems(I); Heterogeneous Catalysis(II)”

2006-03-06 13:30 - 2006-03-06 16:00
RIES, meeting room
Markus Eiswirth (Fritz-Haber-Institut der Max-Planck-Gesellschaft)
I. Electrochemical Systems1. Dissipation in Periodic Processes Using historical examples, it is discussed why thermodynamics can be regarded as“The Queen of Physics”. Then the minimization of dissipation (i.e. increase of efficiency) in energy-transforming processes is discussed, with emphasis on nonlinear periodic processes. Examples are taken from the transformation of chemical to electrical energy and vice versa.2. TOE: Theory of Electrochemistry Using Maxwell’s theory as starting point the basic equation for electrode dynamics (reaction-migration equation) is derived. (Some aspects of advanced calculus are briefly reviewed.) The crucial role of electrode geometry is described. Theoretical results for different electrodes (such as ring, disk, ribbon) are compared to experiments.3. Waving in the Distance: Remote Triggering in Electrochemical Systems Trigger waves are a very wide-spread phenomenon, such as ripples on the surface of water or waves of activity in certain chemical or biological media (e.g. nerve axons). They usually originate from the location where a perturbation (trigger) has been applied, be it a stone thrown into a pond or an electrical stimulus applied to an axon. It is shown that in electrochemical systems an appropriate perturbation at one location can cause the emergence of a wave at a distant place. The experimental findings can be reproduced with the corresponding reaction-migration equations.4. Pulse Waves in an Electrochemical System Electrochemical systems offer a large variety of spatiotemporal patterns. We shall report on a case study of a single such pattern, namely a pulse on a ring electrode, describing its creation, existence region, perturbation and interaction with defects. The possible relevance for pulses in biological excitable media (such as nerve axons) is discussed.II. Heterogeneous Catalysis1. Deterministic and Stochastic Modelling of Catalytic Processes The rich variety of patterns forming on catalytic surfaces at low pressure under isothermal conditions are briefly reviewed (exemplified with the CO oxidation on Pt). It is shown that a deterministic model using reaction-diffusion-equations is appropriate for low pressures ( up to about 0.01 mbar). However, for higher pressures, temperature changes as well as stochastic effects come into play. It is shown how these phenomena can be successfully modelled.