Single Nanoparticle Photoelectrochemistry: Effect of Electronic Structure and Metal Contact on Hole Transfer Rates

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Dr. Mario Alpuche at the University of Nevada-Reno is studying the limits of light-driven reactions at the surfaces of semiconducting nanoparticles. Nanoparticles are about a million times smaller than the period at the end of this sentence, and they exhibit unique properties that make them useful in technologies ranging from consumer electronics to chemical sensors. Working with his students, Professor Alpuche is using nanoelectrodes to study chemical reactions taking place at the surface of a single nanoparticle following the absorption of light. Their discoveries could lead to new ways of converting sunlight into electricity and chemical fuels. In addition, the project is training the next generation of scientists in the development and use of advanced electrochemcial methods. Dr. Alpuche is also partnering with NevadaTeach, which recruits undergraduate students to become K-12 science teachers, and through partnership with the Western Alliance to Enhance Student Opportunity (WAESO) program, he is providing research opportunities to Hispanic students in Northern Nevada, motivating them to pursue careers in chemistry. Dr. Mario Alpuche's research group is studying the fundamental electron transfer events that take place at the surfaces of semiconductor nanoparticles in photo-electrochemical devices. In their experiments, TiO2 and CdSe nanoparticles are attached to nanoelectrodes and excited with light, producing electron-hole pairs. While the electrode detects the photogenerated electrons as a current, the hole in the valance band can be filled by electron transfer from a molecule in solution, or it can become trapped at a surface defect site. The photoinduced current is then measured as a function of electrochemical potential and light intensity. The electron-hole recombination, hole-trapping, and charge transfer processes are disentangled by modeling their experimental observations using finite element simulations. In addition, the group continues to advance the electrochemical instrumentation, including the fabrication of new electrodes with nanometer dimensions, to improve the sensitivity of the technique.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.