Enhanced lightweight, moisture-resistant, and thermoelectric cement composites using carbon nanotube and Hollow glass microsphere-based hybrid clusters

This study presents a novel strategy to enhance the thermoelectric performance of cement-based composites by incorporating hybrid clusters composed of carbon nanotube (CNT) and hollow glass microsphere (HGM), denoted as CNT@HGM. First, the formation and interfacial characteristics of CNT@HGM hybrid clusters were analyzed using SEM, FT-IR, Raman spectroscopy, and zeta potential measurements. Second, a range of CNT and HGM combinations were evaluated to identify the optimal composition for thermoelectric energy harvesting. Third, the influence of moisture ingress and cyclic moisture exposure on thermoelectric performance was assessed, leveraging the superhydrophobic properties of HGM to enhance durability. Finally, composites with optimized CNT and HGM contents were connected in series to construct modular systems, and their electrical behavior was further analyzed using lumped equivalent circuit modeling. The experimental results demonstrated that the incorporation of CNT@HGM significantly improved thermoelectric performance. The composite containing 0.1 wt% CNT and 20 wt% HGM achieved a Seebeck coefficient of 594.2 µV/K, a power factor of 9.85 × 10⁻¹¹ W/mK², and a dimensionless figure of merit (ZT) of 5.02 × 10⁻⁸. When integrated into a series-connected modular system, the Seebeck coefficient, power factor, and ZT increased to 7009.6 µV/K, 1.73 × 10⁻⁹ W/mK², and 8.80 × 10⁻⁷, respectively. These findings highlight the potential of CNT@HGM hybrid clusters for developing high-performance, moisture-resistant thermoelectric cement composites, offering scalable and sustainable solutions for low-grade thermal energy harvesting in civil infrastructure.