Articles you may be interested inFabrication of Cu/Co bilayer gate electrodes using selective chemical vapor deposition and soft lithographic patterning

Experimental standing wave oscillations of the interfacial potential across an electrode have been observed in the electrocatalytic oxidation of formic acid on a Pt ring working electrode. The instantaneous potential distribution was monitored by means of equispaced potential microprobes along the electrode. The oscillatory standing waves spontaneously arose from a homogeneous stationary state prior to a Hopf bifurcation if the reference electrode was placed close to the working electrode. Reduced electrolyte concentrations resulted in aperiodic potential patterns, while the presence of a sufficiently large ohmic resistance completely suppressed spatial inhomogeneities. The experimental findings confirm numerical predictions of a reaction-migration formalism: under the chosen geometry, a long-range negative potential coupling between distant points across the ring electrode can lead to oscillatory potential domains of distinct phase. It is further shown that the occurrence of oscillatory standing waves can be rationalized as the electrochemical equivalent of Turing's second bifurcation (wave bifurcation). In the presence of an external resistance, the coupling becomes positive throughout and leads to spatial synchronization.

In the potentiostatic electrochemical oxidation of formic acid on a platinum ring electrode under bistable conditions, an appropriate perturbation at one location of the ring can cause the emergence of a wave on the opposite side (remote triggering). These findings can be rationalized in terms of the nonlocal coupling function of the system and are theoretically reproduced by solution of the corresponding reaction-migration equation.

We report experimental observations of the spatio-temporal dynamics in the electro-oxidation of formic acid on a Pt ring electrode modified by bismuth adatoms. Bismuth modification significantly enhanced the current density and it was found to considerably increase the existence range of oscillations and spatio-temporal self-organization. Hidden negative differential resistance and the existence of a Hopf bifurcation were deduced from the electrochemical impedance spectra and the occurrence of galvanostatic oscillations. The pattern formation resulted from hybrid effects of the nonlinear chemistry during formic acid oxidation and the long-range coupling of the interfacial potential induced by the chosen geometry (ring type) of the working electrode. Reversible transitions between traveling pulses and oscillating standing waves were observed when the outer potential or the formic acid concentration near the electrode were used as control parameters. Experimental results were compared with computer simulations of a reaction-migration system. The role of electrode inhomogeneities in pattern formation and the transform between patterns were discussed

Experiments on the catalytic reduction of NO with CO on a Pt(100) surface reveal attractive interaction between pulses leading to the eventual merging of two pulses to a single one. The results can be reproduced with a realistic reaction-diffusion model which yields a negative slope in the dispersion relation over a large range of the interpulse distance. [S0031-9007 (99)08476-8] PACS numbers: 82.65.Jv, 05.70.Ln