Electrochemistry Under Confinement: Controlling Dynamics in Nanochannels via Tunable Mass Transport

Abstract

This dissertation explores the intersection of electrochemistry and transport dynamics under confinement using electroanalytical techniques to both probe and control transport behavior. We first present a unique wireless method for in situ control of single metal nanowire growth in a silica nanochannel template. Growth is initiated by direct chemical reduction of metal precursor ions and proceeds until the channel diameter is blocked. Further deposition occurs by a bipolar electrochemical mechanism, in which oxidation at one end of the wire is directly coupled to reduction at the other. The deposition rate can be precisely controlled without a direct electrical connection by applying an electric field during the growth process, offering an unprecedented level of synthetic tunability. Next, we report a comprehensive study of anomalous size- and material-dependent selectivity observed in the transport of polystyrene and silica nanoparticles through a silica nanochannel as detected by resistive-pulse sensing. We investigated several possible contributing factors, including basic driving forces and more subtle nanoscale effects, finding that selectivity occurs outside the channel and may be a result of dynamical charge effects related to interfacial structure or particle polarizability. Our results suggest that nanoscale effects can have a dramatic impact on more macroscale transport behavior when the size of the analyte approaches the size of the channel, which has important implications for both understanding and designing nanoporous systems. We then discuss two new methods for the fabrication of individual gold nanoelectrodes based on reported nanowire synthesis techniques (nanoskiving and lithographically patterned nanowire electrodeposition (LPNE)) and conclude by summarizing efforts to prepare uniform gold nanowire arrays for use in electrochemical sensing and imaging studies. This work reflects the complicated interplay of driving forces inherent in nanoscale systems and demonstrates the exciting potential for harnessing them in a concerted manner to precisely control transport dynamics. Gaining a better understanding of these interactions and determining the relative roles of intrinsic material properties and experimental factors will not only provide the framework necessary to investigate and interpret other fundamental nanoscale processes, but will also enable the design and synthesis of nanomaterials with more tailored and customizable properties for use in catalysis, sensing, and energy applications.