Oriented High Thermal Conductivity Solid-Solid Phase Change Materials for Mid-Temperature Solar-Thermal Energy Storage

As the global energy crisis intensifies, the developmentof solarenergy has become a vital area of focus for many nations. The utilizationof phase change materials (PCMs) for photothermal energy storage inthe medium temperature range holds great potential for various applications,but their conventional forms face several challenges. For instance,the longitudinal thermal conductivity of photothermal PCMs is inadequatefor effective heat storage on the photothermal conversion surface,and there is a risk of leakage due to repeated solid-liquidphase transitions. Here, we report a solid-solid phase changematerial, tris-(hydroxymethyl)-aminomethane (TRIS), which has a phasechange temperature of 132 degrees C in the medium temperature range,enabling high-grade and stable solar energy storage. To overcome thelow thermal conductivity problem, we propose a large-scale productionof oriented high thermal conductivity composites by compressing amixture of TRIS and expanded graphite (EG) using the pressure inductionmethod to create in-plane highly thermally conductive channels. Remarkably,the resulting phase change composites (PCCs) exhibit a directionalthermal conductivity of 21.3 W/(m center dot K). Furthermore, the high phasechange temperature (132 degrees C) and large phase change entropy (213.47J/g) enable a large-capacity high-grade thermal energy to be used.The developed PCCs, when combined with selected photo-absorbers, exhibitefficient integration of solar-thermal conversion and storage. Additionally,we also demonstrated a solar-thermoelectric generator device withan energy output of 93.1 W/m(2), which is close to the powerof photovoltaic systems. Overall, this work provides a technologicalroute to the large-scale fabrication of mid-temperature solar energystorage materials with high thermal conductivity, high phase changeenthalpy, and no risk of leakage, and also offers a potential alternativeto photovoltaic technology.