Spectroelectrochemistry of Redox-Active Colloidal Nanocrystals

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It is now possible to grow crystals from many different semiconductors that are just a few nanometers in size, or about 100,000 times smaller than a strand of hair. At these very small sizes, semiconductor nanocrystals take on novel physical and chemical properties that can be adjusted by changing their size, shape, and chemical composition, making them attractive for use in many next-generation photonic and energy technologies. Although they hold great promise, these nanocrystals also present unique challenges. For example, as one charges a nanocrystal up by adding electrons, it can change color and new chemical reactions can take place at its surface. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Daniel Gamelin of the University of Washington is studying how electrons that are transferred into (and out of) semiconductor nanocrystals alter their physical properties and chemical reactivity. Working with his students, Professor Gamelin is developing new experimental methods that enable them to precisely alter the nanocrystal charge while monitoring changes in their physico-chemical properties. Their discoveries could have important implications for new technologies in energy conversion, energy storage, and efficient energy usage. The project is also providing advanced interdisciplinary education and training for students, preparing them to be future leaders in science, engineering, technology innovation, and education. Integration of research and education is emphasized through involvement of undergraduates in the project, incorporation of project concepts into the UW undergraduate laboratory curriculum, and outreach activities at Seattle K-12 schools and community STEM events.Despite extensive studies and progress in controlling the formation of high-quality colloidal reduced or oxidized semiconductor nanocrystals over recent years, the redox properties of colloidal nanocrystals remain poorly understood, particularly in the multiple-carrier regime relevant to charge-tunable plasmonics, high-density charge storage, or multi-electron catalysis. This project targets the development and application of new methods for measuring, controlling, and understanding the properties of redox-active colloidal semiconductor nanocrystals emphasizing spectroelectrochemical probes of nanoscale chemical transformations. The goal is to elucidate the redox reactivities and associated physico-chemical properties of such nanocrystals that possess excess delocalized electrons or holes. Specific nanocrystal research foci include: metal-coupled electron-transfer reactions relevant to charge-tunable plasmonics, soluble supercapacitors relevant to energy storage, and band-edge potentials of nanostructures relevant to photochemistry and electron transfer. All of these are anticipated to play central roles in future nanocrystal technologies. Spectroelectrochemical potentiometry has been identified as a particularly powerful and quantitative probe of the redox properties of free-standing colloidal semiconductor NCs, and it is enabling unique in situ monitoring of nanocrystal redox manipulations and composition transformations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.