Light-Powered Plasmonic Heaters: Extracting the Heat Out of Plasmons for Photothermal Applications

Abstract

The thermal energy (heat) dissipated during light-matter interactions is considered as a ‘loss’ in energy science. However, this process of heat dissipation is inevitable in all light-matter interactions. Recently, attention has gained towards designing systems that can generate and dissipate large amount of heat, so that they can be used for various applications. Plasmonic nanomaterials are one of the promising materials that can generate and dissipate huge amount of heat upon illumination. This dissipated heat is termed as ‘plasmonic heat’ and the area that studies this plasmonic heat is defined as ‘thermoplasmonics’. There are multiple theoretical studies in this domain on the generation, dissipation, timescale, factors and so on, with very limited experimental validations. The proposed thesis is an effort to provide adequate experimental results on the factors influencing the generation, dissipation, quantification, and utilization of plasmonic heat. In one of the studies, insights into the effect of shape and geometry on the generation of plasmonic heat were provided. Here, an assembled-geometry (bundled nanowires) was found to be a better nanostructure to generate the plasmonic heat, compared to the spherical counterpart. Photothermal experiments such as polymerization, solar-vapor generation, and Diels–Alder reaction, were used as a proxy to quantify the plasmonic heat dissipated by various nanostructures. Next, a novel quantification technique based on the property of ‘thermochromism’ was developed to qualitatively quantify plasmonic heat close to the surface of nanomaterials. This approach is a cost effective and reliable technique, which was validated with standard quantification techniques based on melting point, Raman, and IR imaging. In another study, the role of hot-charge carriers was separated from plasmonic heat in a photothermal chemical reaction. An ingenious design of a closed reactor setup was used to perform solar driven Claisen rearrangement reaction, which prevented the flow of hot-charge carriers into the reaction. This led to a sole plasmonic heat-driven high-temperature chemical transformation. In another set of studies, the plasmonic heat generated under sunlight illumination was converted into electricity through solar thermoelectric generators (STEG). The incorporation of AuNPs as the solar absorber led to ~9 times enhancement in the overall solarto-electricity conversion efficiency of concentrated-STEG (under 75 sun), with an efficiency of 9.6% at ambient conditions. This, to the best of our knowledge, is the highest efficiency reported for STEGs at ambient conditions. The electricity generated from the plasmon-powered STEG was used to run low-to-medium power electrical devices (35 mW to 500 mW), as well as for the green-H2 production via the electrolysis of water.

Thus, various aspects of thermoplasmoincs including generation, quantification, utilization and conversion of plasmonic heat were studied in detail. Alongside, the plasmonic heat was used for performing energy-intensive chemical transformations, which showcases the suitability of plasmonic heat in high-temperature applications. In short, our studies demonstrate that plasmonic heat could emerge as a greener alternative to conventional thermal energy sources in science and engineering.