Abstract
Numerous electrochemical systems exhibit spontaneous, dynamical
instabilities upon sufficient displacement from chemical equilibrium
by means of an overvoltage (spontaneous self-organization). The
most inportant regimes emerging from a single, stable state are
bistability, kinetic oscillations or deterministic chaos. Also,
in the presence of an appropriate spatial coupling allows the
occurrence of complex spatial regimes such as propagating or stationary
waves.
In the present thesis, spontaneous current oscillations during
the electrocatalytic oxidation of formic acid on platinum was
investigated both experimentally and theoretically. A kinetic
model allowed the simulation of relevant dynamical features and
resulted in a detailed mechanistic understanding of the underlying
reaction processes.
Spatially resolved measurements of the local electrode potential
along a ring electrode (the reference electrode being in the center)
revealed intriguing spatially inhomogeneous behavior of the interfacial
potential: ´Remote triggering´ of activation fronts under bistable
conditions and ´Standing Potential Waves´ indicated a negative
non-local migration coupling across the electrolyte.
Another chapter deals with the mechanistic basis of current and
potential oscillations during the electroctalytic reduction of
iodate on noble metal electrodes. A simple kinetic model again
helped elucidate the underlying destabilizing electrochemical
mechanism.
Finally, experimental feedback control methods - applied to electrochemical
oscillators - were shown to provide valuable information for the
assignment of mechanistic roles to individual chemical species.
Based on information known from literature and all information
gathered from the present thesis, the last chapter suggests a
mechanistic classification scheme of oscillatory, electrochemical
systems. Moreover, an experimental, operational method was proposed
for the purpose of a systematic, stepwise classification of unknown
electrochemical oscillators.
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