Expanded Graphite/Cement Composites for Large-Scale Energy Harvesting: Structural Control and Thermoelectric Properties

Building structures exposed to direct sunlight for long periods of time accumulate large amounts of low-grade thermal energy. Cement-based composites with expanded graphite (EG) have excellent thermoelectric properties and can utilize the thermoelectric effect to convert heat accumulated in the building structure into electrical energy, showing great potential advantages for large-scale heat harvesting and energy supply, but the contribution of the particle size of EG and the composition of cement clinker minerals to the thermoelectric properties of EG/cement-based composites is unknown. In this article, EG/cement-based composites were prepared by etching EG of different particle sizes as the conductive phase with acid solution, and the thermoelectric properties of the EG/cement-based composites were enhanced by the synergistic effect of multiparticle size EG, which significantly improved the connectivity of the EG conductive network. The high-purity cement clinker monominerals C₂S and C₄A₃S̅ were further prepared, and the results showed that the synergistic effect of C₂S and C₄A₃S̅ improved the carrier mobility in the EG/cement-based composites, with electrical conductivities, Seebeck coefficients, and power factors reaching 7.43 S/cm, -65.69 μV/K, and 3.23 μW m^-1 K^-2, and the power factors of EG/C₂S-C₄A₃S̅ are improved by 1.21 and 2.16 times, respectively, compared to those of EG/C₂S and EG/C₄A₃S̅.