Active spatiotemporal control of electrochemical reactions by coupling to in-plane potential gradients

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 O-2 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 C-8 or longer. Spatially directed Cu deposition on All was demonstrated by forming Cu stripes on All, 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 All 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.