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Chemistry
Chemistry Defense: Joey Offen: Addressing the Key Challenges of Light Penetration and Charge Separation for Plasmonic Catalysis
Tuesday, November 11,
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Speaker(s): Joey Offen
Addressing the Key Challenges of Light Penetration and Charge Separation for Plasmonic Catalysis
Research into high temperature photocatalysis has revealed advantages to using light to augment or replace thermal energy for the synthesis of feedstock chemicals. However, poor penetration of light into a typical powder catalyst bed poses a challenge for efficient high temperature photo-driven heterogenous catalysis. To address this issue, we present a 3D porous optical diffuser loaded with plasmonic Rh nanoparticles enabling volumetric illumination of the nanoparticle catalysts. This monolithic plasmonic Rh/SiO2 structure exhibits dramatically increased response to light compared to powdered catalyst. The broad illumination gradient can be tuned by augmenting the loading scheme creating a more homogenous optical environment. Replacing the sharp transition from intensely illuminated surface to dark subsurface improves the selectivity of the CO2 reduction reaction from 68% to 97% while achieving greater efficiency. A sacrificial template composed of fused zinc oxide tetrapods enhances porosity, improving mass transport over conventional aerogel supported catalysts. Serendipitously, the ZnO scaffolding implemented to improve mass flow also provides easier nanoparticle loading as well as the potential for more facile adjustments to the aerogel's surface chemistry. This approach to supported photocatalyst design provides exceptional flexibility for tuning the balance between optical properties, mass flow considerations, available metal surface area, at a cost to thermal transport. A second challenge facing plasmonic catalysis is the short charge separated lifetime of hot carriers produced by plasmon dephasing, typically on the order of femtoseconds. The latter portion of this dissertation explores the introduction of a type-II junction to the supporting structure to further separate carriers, prolonging excited lifetimes.
Research into high temperature photocatalysis has revealed advantages to using light to augment or replace thermal energy for the synthesis of feedstock chemicals. However, poor penetration of light into a typical powder catalyst bed poses a challenge for efficient high temperature photo-driven heterogenous catalysis. To address this issue, we present a 3D porous optical diffuser loaded with plasmonic Rh nanoparticles enabling volumetric illumination of the nanoparticle catalysts. This monolithic plasmonic Rh/SiO2 structure exhibits dramatically increased response to light compared to powdered catalyst. The broad illumination gradient can be tuned by augmenting the loading scheme creating a more homogenous optical environment. Replacing the sharp transition from intensely illuminated surface to dark subsurface improves the selectivity of the CO2 reduction reaction from 68% to 97% while achieving greater efficiency. A sacrificial template composed of fused zinc oxide tetrapods enhances porosity, improving mass transport over conventional aerogel supported catalysts. Serendipitously, the ZnO scaffolding implemented to improve mass flow also provides easier nanoparticle loading as well as the potential for more facile adjustments to the aerogel's surface chemistry. This approach to supported photocatalyst design provides exceptional flexibility for tuning the balance between optical properties, mass flow considerations, available metal surface area, at a cost to thermal transport. A second challenge facing plasmonic catalysis is the short charge separated lifetime of hot carriers produced by plasmon dephasing, typically on the order of femtoseconds. The latter portion of this dissertation explores the introduction of a type-II junction to the supporting structure to further separate carriers, prolonging excited lifetimes.
