Encapsulation and 3D Printing of Salt Hydrates for Thermal Energy Storage

Thermal energy storage technologies are crucial for the growth of sustainable energies due to the intermittent nature of many renewable energy resources. Salt hydrates, a class of phase change materials (PCMs), are promising as low-cost, high volumetric energy density media for latent heat storage. However, their inherent limitations such as undercooling and incongruent melting render them unstable for extended thermal cyclability. Microencapsulation can mitigate some of these challenges, enhance heat transfer efficiency, and minimize moisture loss/gain from the external environment to improve PCM performance. We demonstrate the use of non-aqueous Pickering-type emulsions, stabilized by alkylated graphene oxide (GO) nanosheets, as templates for subsequent precipitation of commodity polymers to access core-shell microcapsules loaded with salt hydrates. These microcapsules are robust to thermal cycling, exhibit minimal undercooling in comparison with the bulk salt hydrate, and have a high loading (~90 wt%) of pristine core material. Further, this single-step, highly tunable approach is amenable to different salt hydrates as cores and different polymers as shell materials, making it suitable for tailoring capsule properties. Alternatively, we have formulated functional inks containing salt hydrate PCM particles as rheological modifiers in polymer solutions; eliminating the need for prior microencapsulation of the PCM. These inks are then 3D printed into complex hierarchical structures using a direct ink writing technique. This approach affords excellent passive thermoregulation properties to the fabricated composites, representing a significant advancement in developing materials aimed towards energy management and sustainability.