Design of Photonic and Plasmonic Materials for Photocatalytic CO2 Reduction

Abstract

This work explores the effects of photonic structuring and localized surface plasmon resonance (LSPR) and on CO2 reduction reactions (CO2RR). We design photonic crystals where the photonic bandgap is tuned by changing the periodicity of the inverse opal cavities. The photonic bandgap of an inverse opal structure can be tuned by the material and pore size/periodicity. These photonic properties control how the incoming light is reflected and refracted within the material. We investigate a variety of photonic crystal materials, such as metal oxides, by infilling the voids of an opal template of polystyrene (PS) spheres to obtain an inverse opal photonic crystal by subsequently removing the PS spheres. Similarly, the LSPR can be tuned in metal or degeneratively doped semiconductor nanoparticles by tuning the size, shape, and material composition. This increases absorption near the resonance peak. Additionally, hot carriers can be generated as the LSPR decays, providing the potential to access kinetic pathways normally difficult for desired products in CO2RR chemistry. Since we can tune the photonic bandgap simply by changing the size of the PS spheres in the template, we can investigate how matching the photonic bandgap with the plasmonic resonance of a metal particle affects CO2 reduction. We then study the effects of combining both of these physics phenomena on chemical transformation and selectivity in CO2 reduction. From this basis, one could potentially tune CO2RR processes to a desired hydrocarbon fuel product. We use a combination of SEM, TEM, and XRD to analyze the morphological structure and crystallinity of our materials as well as material composition via EDX. Surface analysis of our structures is done using XPS. We characterize the films’ optical properties, monitoring shifts in the photonic bandgap and LSPR, via UV-Vis-NIR spectroscopy. We monitor CO2 reduction products using in line GC for gas products and NMR for liquid products.