Coupling and Spatiotemporal Structure in Electrochemically Reacting Systems

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

Abstract - Hudson - 0000483 Temporal and spatial variations in concentration, temperature, and potential occur in many reacting systems including liquid and gas phase reactions, gas-solid heterogeneous reactions, and biochemical reactions; such nonuniformities can have a strong effect on the overall rate of reaction as well as the system dynamics. In this work, the PI plans to carry out experimental studies on spatiotemporal patterns and coupling among reaction sites during electrochemical reactions. He plans to use several techniques to study the temporal and spatial structures. The time and space scales are interrelated because of interactions through the potential and concentration fields with the length scale generally decreasing with increasing frequency. Some of the studies will be done using arrays of electrodes to measure the current, or rate of reaction, independently at many locations on the reaction surface. The method is applicable to all types of electrochemical reactions over a large range of conditions since the current is measured at each electrode at a high sampling rate. The length scale of the reaction surface is varied by changing the number of electrodes in an array, the size of the individual electrodes, or the spacing among the electrodes. Electrochemical reactions are strongly coupled through the electric field, i.e., long rage coupling plays in important role in the system characteristics. The PI plans to use a novel experimental setup to study the effects of global coupling during metal electrodissolution reactions. Through the use of a set of individual and collective external resistors he is able to vary the degree of global coupling without changing the other parameters of the system. The dependence on coupling strength will be determined; transitions form disordered (turbulent) to ordered or coherent states and the occurrence of synchronized and clustered states will be studied. The PI also plans to study the impact of temporal and spatiotemporal forcing. Such forcing, sometimes called charge modulated electric fields, is useful in applications such as the manufacture of multilayered GMR materials and the superfilling of vias for interconnect technology. He will investigate copper deposition under pulsed conditions with an emphasis on the resulting spatial structure. Microstructuing using ultra-short pulsed voltage inputs will also be investigated. The reduction in size of electronic devices has led to the search for new technologies for the manufacture of on-chip interconnects. The high-frequency methods the he will be investigating may lead to greatly improved spatial resolution. In addition, the electrode arrays will be used in the forcing studies. He will investigate the ordering of spatiotemporal chaos with inputs to a single channel of an array. Such ordering is complicated due to the existence of numerous unstable spatial modes but such ordering is important in plasma, laser devices, and in both chemical and biological systems where variations in both time and space occur. Finally, he plans to look at the effects of temporal and spatial forcing on electrocatalytic reactions of interest in fuel cell applications, the oxidation of hydrogen and of small organic compounds. By using addressable microarrays the PI will investigate the possible influence of temporal forcing on reaction rate, likely through the removal of inhibitors from the surface, and also the effect of the input of impulses of varying spatial scale on activation.