Size-dependent electrochemistry of redox active nanoparticles

Size-dependent electrochemistry of redox active nanoparticles Size-dependent electrochemistry of redox active nanoparticles This project will explore the influence of size on the electrochemical behavior of metal and metal oxide nanoparticles (NPs). Particular focus will be on the effects of surface stress on electrochemical behavior at the nanoscale. Systems that will be examined include discrete NPs of Ag, Pd and MnO2, all of which are relevant in the area of electrochemical energy storage and conversion The newly discovered Ag and Pd NPs are capped with adenosine triphosphate, ATP. They can be isolated as solids and dissolved at high concentrations in aqueous supporting electrolytes, thus enabling facile study of their electrochemical behavior in thin layerby- layer films and as individual, dissolved NPs. The MnO2 NPs have been previously reported, but their electrochemical behavior has not been examined thoroughly. Both types of NPs will be assembled into layer-by-layer films so their electrochemical behavior can be examined. The ability to make these NPs in different sizes will be exploited to evaluate the size dependence of their redox activity. The Pd NPs have interesting H2 storage behavior. The size dependence of this also will be explored. Layered MnO2 NP are potentially attractive as cathode materials for Li+ insertion secondary batteries. Preliminary work with MnO2 NPs in the context of energy storage suggests that there is a size dependent structural transformation that converts a layered structure with highly desirable energy storage properties into a spinel structure with much less desirable properties. The work proposed here seeks to understand at a fundamental level how to control this phase transformation by using nanoscale materials. Thus, the origins of this important size-dependent behavior will be elucidated. Intellectual Merit. In spite of a large literature on the physical properties of nanoscale materials, including many studies of their thermodynamic behavior, the exploration of how size influences the faradaic redox chemistry of nanoscale materials is just in its infancy. Theory suggests that surface effects, especially surface stress, can produce marked changes in redox potential for nanoscale materials and in relative phase stability (e.g. layered vs. spinel lithium manganese oxide). However, little experimental data on well-defined, discrete nanoparticulate materials are available to test and refine theory. A goal of this work is to elucidate these effects so the potentially significant influence of surface stress can be captured and controlled in new nanoscale materials.