Ultra Low-Cost Phase Change Hydrogel for Building Thermal Regulation

Energy-efficient thermal management for buildings is one of the keys to our sustainable future, as the demand for thermal comfort has increased swiftly under the impact of extreme weather. Tremendous research endeavors have been reported in recent decades, striving to tackle thermal management tasks using sustainable methods such as radiative cooling, evaporative cooling, and smart window. Thermal energy storage (TES), which utilizes latent heat of phase change materials (PCMs), also received emerged interest for its ability in mitigating temperature fluctuations and sustaining thermal comfort without extra energy input. However, practical implementation of PCMs is constrained by cost, shape stability, and energy density. Here we report an inorganic PCM composite based on sodium sulfate decahydrate (SSD). In contrast to most organic PCM, SSD has an ultralow cost (1.60 $/kWh) and high energy density (254 J/g), making it a promising PCM for building thermal management. To address the intrinsic limitations of SSD in shape stability and phase separation, we introduced another low-cost hydrogel, i.e., poly (acrylamide-co-acrylic acid), to encapsulate SSD through swelling. In particular, we optimized hydrogel composition by exploring the hydrolysis effect, and achieved a swelling ratio of 29.96 g/g in 70 wt% SSD solution. The obtained phase change hydrogel exhibited a melting latent heat of 133.32 J/g with melting temperature of 32.84 °C, while withholding excellent shape stability after 500 hundreds thermal cycles. This demonstrated thermal properties promise a cost-effective PCM for building thermal regulations.