Self-dispersible SiO2@CrGO molten salt nanofluids for medium-temperature direct absorption solar-thermal energy harvesting

Abstract

Molten salt nanofluids have emerged as an appealing medium for direct absorption-based harvesting of solar-thermal energy at elevated temperatures. Most often, however, molten salt nanofluids suffer from poor dispersion stability and tend to aggregate, which is challenging to solve with conventional stabilization approaches. In this work, we report the preparation of crumpled hybrid SiO₂@CrGO particles that are self-dispersible within molten salts for direct absorption-based medium-temperature solar-thermal energy harvesting. The crumpled hybrid SiO₂@CrGO particles were synthesized through attaching SiO₂ nanoparticles onto GO sheets with silane coupling agents followed by a one-step aerosol drying process. By controlling the loading of SiO₂ particles, the hybrid SiO₂@CrGO particles possess crumpled rough surface structure and an appropriate density matching with the molten salt fluids. Such features simultaneously suppress interparticle van der Waals attraction and gravitational sedimentation or buoyancy-induced floating, which in turn enable stable homogeneous dispersion of the nanofluids after continuous heating at 200 °C for 30 days and concentrated solar illumination. In comparison with neat molten salts, the SiO₂@CrGO nanofluids have demonstrated long-term stable uniform dispersion, significantly increased solar absorptance, slightly enhanced specific heat capacity and largely same solid-liquid phase change behavior, which enabled consistent direct absorption of concentrated solar illumination as renewable heat at 200 °C. It is expected that this work provides a facile and effective strategy to overcome the long-lasting dispersion stability issue of molten salt nanofluids and stimulate their diverse applications.