Phillip Christopher
The Physics & Astronomy Colloquium Series presents Phillip Christopher of the University of California, Riverside on “Plasmons, Hot Electrons and Their Potential for Solar Driven Chemical Conversion” on Friday, Feb. 20, at 4:10 p.m. in Walter 245.
Abstract: The average solar irradiance provides ~50,000X times more energy to the earths surface than the average primary human energy consumption rate. This vast potential drives interest in converting solar energy into electrical energy using photovoltaics and into chemical fuels and commodity chemicals using light harvesting catalysts. While photovoltaics are implemented practically at an increasing rate, utilization of solar energy to drive chemical conversion is in technological infancy due to additional complexities. Two primary issues with solar photons are the highly diffuse (low flux) and broadband (continuous distribution of wavelengths) nature of black body irradiation. In this talk I will provide an overview and examples of how localized surface plasmon resonance (LSPR) excitation on nanoparticles may alleviate some of these issues.
The excitation of LSPR occurs when a nanostructured material with high free electron mobility interacts with photons that match the resonance energy of the oscillation of surface valence electrons against the restoring force of the positively charged surface nuclei. As a result of very high absorption coefficients of photons with energies matching the LSPR and capacitive coupling between clusters of plasmonic particles, LSPR excitation produces huge electromagnetic (EM) fields and high concentrations of energetic electrons at nanostructured surfaces. Recently we showed that strong EM fields produced from LSPR excitation on Ag nanoparticles could enhance photochemistry on the surface of nearby semiconductors, opening avenues for driving solar fuel production reactions more efficiently. Furthermore we found that chemical reactions could be driven directly on the surface of nanostructures through the transfer of plasmon derived hot electrons into antibonding orbitals of adsorbed reactants. The hot electron mediated reaction mechanism allows for execution of unique selective chemistry through matching of hot electron energy to the energy of unpopulated adsorbate orbitals. In both mechanisms, it is proposed that “hot‐spots” formed at the junctions of plasmonic nanoparticles play a critical role in maximizing solar‐to‐chemical conversion efficiency. Mechanistic details and potential approaches to optimize plasmon‐mediated chemical conversion will be discussed.
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