Active spatiotemporal control of electrochemical reactions through dynamic electrochemical potential gradients was explored by investigating three different types of reactions on Au:  alkanethiol SAM electrosorption, Cu deposition and stripping, and O2 evolution from H2O2 oxidation. Counterpropagating gradients composed of two different thiols differing either in terminal functionality or in chain length were prepared, and their kinetic and environmental stability was inferred from spatially resolved contact angle measurements for samples stored under varying environmental conditions for periods up to one month. Chain length was found to correlate strongly with stabilitya requirement for stability being that at least one of the chains be at least C8 or longer. Spatially directed Cu deposition on Au was demonstrated by forming Cu stripes on Au, establishing that a sequence of different potential gradients could be used to define an area of deposition in the center of a working electrode. Dynamic spatiotemporal control of Cu deposition on Au was achieved by translating a potential window, which encompassed the Cu redox waves, across the Au surface. The position of the Cu/Au transition was constant at a potential intermediate between the two waves, and the width of the transition region in the SPR images was narrower than either of the two electron transfer waves. Spatially directed oxidation of H2O2 was demonstrated by monitoring the formation of oxygen bubbles near the electrode. Consistent with predictions of the Butler−Volmer equation, the rate of bubble formation was found to depend on spatial position (overpotential) in these experiments.

Charge-selective electrochemistry was previously shown to occur at high surface area carbon fibers that were produced by fracturing the outer periphery with anodic current or positive potential. The cyclic voltammetric behavior of electroactive species observed at these fibers exhibited a distinct pH dependence related to the protonation/deprotonation of oxygen-containing functional groups at the surface of the carbon fiber. In this paper, electrochemical flow injection analysis (EC-FIA) is used to probe ion partitioning in to and out of the interior microstructure of the treated carbon fiber, for both electroactive and electroinactive species. It was found that the extent of partitioning was the result of both ion charge and hydrated ionic radius, in addition to the level of fracture. It was further observed that the direction of movement for an injected ionic species could be controlled relative to the ion concentration, the pH of the carrier solution, or both. EC-FIA allowed the simultaneous observation of current due to ion movement and that due to electron transfer to a redox-active species. The results presented are consistent with a model in which fixed negatively charged sites in the interior of fractured fibers govern ion partitioning with positively charged ions in the carrier solution, with counterions located in the interior "free" volume.

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