Functional Materials for Solar Thermal Energy Harvesting

Recently, solar heat localization has provided a promising route for efficient solar steam generation and for utilization of solar thermal energy. In this approach, a floating material paradigm localizes the irradiated solar energy forming a hot spot at the liquid- vapor interface. The liquid underneath wicks to the interface for steam generation. In contrast to conventional steam generation systems, thermal losses are reduced significantly, thereby increasing the evaporation efficiency. Due to these unique characteristics, this concept has found a wide array of applications. Here, the concept of solar heat localization is explained along with material properties and the important parameters for the design of these materials. A comparative analysis is conducted for these figures of merit between several studies, and key takeaways are highlighted. New disruptive paths for long term desalination, CO2 capture and 24/7 solar thermal energy harvesting, and storage are developed with high efficiency using this concept. For long-term solar desalination, a new efficient and flexible material structure is developed. The material structure has a porous polymer skeleton with embedded graphite flakes and carbon fibers. The geometry of pores in this structure and their surface characteristics prevent any salt accumulation in the material structure. We have demonstrated five orders of desalination of highly-salty brine (1.52×105 mg/L) in a long- time performance with no change in its efficiency. The performance of this structure in the laboratory and outside environment is assessed. This cost-effective and durable material along with its easy fabrication procedure provides a path toward large-scale efficient solar desalination. For carbon dioxide (CO2) capture and conversion, we report a solid-state sustainable CO2 collector (SCC), which is activated by solar heat localization. This stable cyclic SCC is based on ionic liquids and graphene aerogel, which undergoes solid–liquid phase change to efficiently capture and convert CO2. The SCC captures 0.2 moles of CO2 for every mole of ionic liquid and converts the absorbed CO2 into useful byproducts, including water and calcium carbonate in each cycle. A system prototype of the SCC is developed and demonstrated. The SCC provides a new and promising paradigm to efficiently capture and convert CO2 using abundant solar energy to address global emissions and consequent environmental challenges. For solar-thermal energy-harvesting and storage, we combine the physics of molecular energy and latent heat storage to introduce an integrated harvesting and storage hybrid paradigm for 24/7 energy delivery. The hybrid paradigm utilizes heat localization during the day to provide a harvesting efficiency of 73% at small-scale and ~90% at large- scale. Remarkably, at night, the stored energy by the hybrid system is recovered with an efficiency of 80% and higher temperature than that of the day, in contrast to all the state- of-the-art systems. The integrated hybrid concept and the system open a path for simultaneous harvesting and storage of solar-thermal energy for a wide range of applications, including power-generation, desalination, and distillation.Mechanical Engineering, Department o