Stanford Energy Student Lectures: Renwen Yu and Briley Bourgeois

Renwen Yu

Title: Time-modulated near-field radiative heat transfer

Abstract: We explore near-field radiative heat transfer between two bodies under time modulation by developing a rigorous fluctuational electrodynamics formalism. We demonstrate that time modulation can results in the enhancement, suppression, elimination, or reversal of radiative heat flow between the two bodies, and can be used to create a radiative thermal diode with infinite contrast ratio, as well as a near-field radiative heat engine that pumps heat from the cold to the hot bodies. The formalism reveals a fundamental symmetry relation in the radiative heat transfer coefficients that underlies these effects. Our study indicates the significant capabilities of time modulation for managing nanoscale heat flow.

Bio: Renwen is a postdoctoral scholar in Professor Shanhui Fan’s group at Stanford. He does research in theoretical aspects of nanoscale thermal energy harvesting.

Briley Bourgeois

Title: Understanding photoreactions across multiple length scales – in situ ETEM and reactor-scale studies of plasmonic photochemistry

Abstract: Nanoscale metal structures can very strongly interact with light through a phenomenon called a plasmon resonance. These resonances collectively excite charge carriers in the structure which in turn can drive chemical reactions in unique ways. The behavior of these plasmonic photocatalysts is dictated by the nanoscale structure of the particles. As their size and shape changes, different atomic structures are exposed and the nature in which light is channeled by the particle is altered. These features, while much smaller than can be resolved by a traditional microscope, have a huge impact on the performance of plasmonic photocatalyst. In this work, we utilize in-situ transmission electron microscopy to control and study photochemistry with near-atomic resolution. We show that light can be used to control the presence of hydrogen within plasmonic catalysts and govern the most reactive sites on the catalyst’s surface. We further utilize bench-scale chemistry techniques to demonstrate improved chemical selectivity for hydrogenation chemistries for reactions driven by light instead of heat. With the ability to understand and build photocatalysts from fundamental length scales, better materials can be designed to drive important chemistries using sustainable energy source.