Hydrated salt composites with binary carbon networks and laser-treated hydrophobic surfaces for multifunctional outdoor building thermal management

Integrating low-cost hydrated salt phase change materials (PCMs) into buildings such as sunrooms represents an attractive strategy to mitigate temperature fluctuation caused by weather change and enhance thermal comfort without consuming extra energy. However, hydrated salts usually suffer from strong supercooling, low thermal conductivity, poor solar absorptance and leakage after melting, and conventional composite design cannot simultaneously overcome these shortcomings. In this work, we report the design and fabrication of multifunctional hydrated salt PCM composites through compression molding of sodium acetate trihydrate (SAT), disodium hydrogen phosphate dodecahydrate (DHPD), hydrophilic carbon nanotubes (CNTs) and expanded graphite (EG) into monolithic blocks and subsequent surface cross-hatch laser scanning and wax deposition. The optimal SAT composites loaded with 3 wt% DHPD, 2 wt% CNTs, and 16 wt% EG demonstrate a thermal conductivity of 7.49 W/m·K, a latent heat of 175.5 J/g, and a supercooling degree of 0.72 °C. Laser treatment amplifies surface roughness of the composites, which achieves a high solar absorptance of 97% and creates hydrophobic self-cleaning surfaces for automatic removal of dusts and solar-accelerated deicing. In sunroom thermal management tests, it reduces peak indoor temperatures by 15.3 °C and extends indoor comfortable durations through absorbing excessive solar heating at daytime and releasing stored latent heat after sunset. Such multifunctional hydrated salt PCM composites not only intelligently regulate the indoor temperature of sunrooms but also effectively prevent dust accumulation and ice formation on building surfaces, demonstrating broad applicability for passive thermal management under diverse weather conditions.