Exploring Thermal Photonics for Sustainability: From Selective Solar Absorbers to Terrestrial Radiative Cooling

Citation

Su, Magel Powei (2024) Exploring Thermal Photonics for Sustainability: From Selective Solar Absorbers to Terrestrial Radiative Cooling. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/rrf2-4979. https://resolver.caltech.edu/CaltechTHESIS:06032024-223707990

Abstract

Photonic materials for thermal emission control have attracted much attention in sustainable technologies where energy and heat management are highly desirable. Controlling the frequency dependency of emissivity enables passive suppression or enhancement of thermal emission which can be used to exploit thermodynamically favorable conditions.

In Part I, we present the development of a selective solar absorber which suppresses thermal emission for efficient conversion of solar energy into thermal energy. Our absorber uses an ultrathin metal layer and an antireflective coating to suppress thermal emission and enhance solar absorption, respectively. Furthermore, we constructed a novel scalable photothermal reactor which utilizes the selective solar absorber for thermocatalytic processes. Thermochemical processes provide a sustainable alternative for fuel synthesis compared to traditional industrial methods, and catalyzed processes operate at reduced temperatures and pressures allowing them to be powered solely by direct solar thermal energy. Using sunlight, we synthesized C₆ – C₂₄ carbon chain length olefins from ethylene gas with Ni-catalyzed ethylene oligomerization, demonstrating a vital step for direct CO₂ to sustainable aviation fuel synthesis.

In Part II, we present silicon oxide and silicon nitride bilayer laminate nanoparticle films as scalable efficient daytime terrestrial radiative coolers which couple enhanced thermal emission with the cold background of space. We show experimentally that laminate nanoparticle films deposited from a nonthermal plasma are well described by effective medium mixing models, and their fill fraction tunability enables them to spectrally match more efficiently to the atmospheric transmission window than conventional dense laminate thin films. During this process, we realized a need for directly measuring thermal emission in a controlled ambient to facilitate inter-comparisons between radiative cooling performances. In response, we constructed a new instrument for direct spectrally and angularly resolved radiative emission measurements, providing a new avenue to study the thermal emission behavior of photonic materials.

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