Erythritol impregnated within surface-roughened hydrophilic metal foam for medium-temperature solar-thermal energy harvesting

Abstract Erythritol (ET) has received increasing research attention for medium-temperature phase change solar-thermal energy storage. However, ET suffers from serious supercooling, low thermal conductivity, poor solar absorption and leakage after melting, which lead to low solar-thermal energy harvesting and releasing efficiency. Herein, we simultaneously overcome these inherent shortcomings by impregnating ET within surface-roughened hydrophilic copper foam, which is prepared by subsequent oxidization of commercial copper foam and thermal reduction under hydrogen, and using stably dispersed crumpled graphene particles as the solar-thermal converter. Such oxidization-reduction-treated copper foam not only provides numerous heterogeneous nucleation sites and lowers the nucleation energy barrier for forming ET crystals during the solidification process, but also facilitates rapid charging and discharging along three-dimensional heat conductive networks, and confines the melted ET. Compared with neat ET, the copper foam-templated composites have reduced the supercooling degree by ~60 °C and improved thermal conductivity by more than 5 times, which in turn lead to a large latent-heat releasing percentage of 85.8% and a high heat-extraction efficiency of 94.2%. We demonstrate that such composites can be used for high-efficiency, medium-temperature, form-stable, direct solar-thermal energy harvesting, and the harvested heat can be readily converted into electricity to power small devices.