Printing Composites with Salt Hydrate Phase Change Materials for Thermal Energy Storage

Salt hydrate phase change materials are important in advancing thermal energy storage technologies for the development of renewable energies. At present, their widespread use is limited by undesired undercooling and phase separation, as well as their tendency to corrode container materials. Herein, we report a direct ink writing (DIW) additive manufacturing technique to print noncorrosive salt hydrate composites with thoroughly integrated nucleating agents and thermally conductive additives. First, salt hydrate particles are prepared from nonaqueous Pickering emulsions and then employed as rheological modifiers to formulate thixotropic inks with polymer dispersions in toluene serving as the matrix. These inks are successfully printed at room temperature and cured by solvent evaporation under ambient conditions. The resulting printed and cured composites, containing up to 70 wt % of the salt hydrate, exhibit reliable thermal cyclability for 10 cycles and suppressed undercooling compared to the bulk salt hydrate. Remarkably, the composites consistently maintain their structural integrity and thermal performance throughout the entirety of both the melting and solidification processes. We demonstrate the versatility of this approach by utilizing two salt hydrates, magnesium nitrate hexahydrate (MNH, T_m = 89 °C) and zinc nitrate hexahydrate (ZNH, T_m = 36 °C), to achieve desired thermal characteristics across a wide range of temperatures. Further, we establish that the incorporation of carbon black in these inks enhances the thermal conductivity by at least 33%. This approach consolidates the strengths of additive manufacturing and salt hydrate phase change materials to harness customizable thermal properties, well suited for targeted thermal energy management applications.