Synergistic enhancement of power factor and figure-of-merit in tin sulfide-expanded graphite cementitious composites by silica fume and fly ash

Thermoelectric materials, which enable the direct conversion of heat energy into electricity, have broad applications in waste heat recovery, low-energy snow and ice melting, urban heat island mitigation, and renewable energy systems. However, conventional thermoelectric materials, such as PbTe and Bi₂Te₃, fly ashce limitations due to their high cost, scarcity, and potential toxicity. Utilizing solid waste materials to enhance the performance of thermoelectric materials offers a dual benefit: reducing production costs and promoting the resourceful utilization of waste. Currently, the thermoelectric properties of cementitious composites are primarily constrained by their high carbon content, low Seebeck coefficients, and poor electrical conductivity.

In this study, for the first time, two solid waste materials-silica fume (SF) and fly ash (FA) were incorporated into tin sulfide (SnS) carbon fiber (CF) expanded graphite (EG) cementitious composites to improve their thermoelectric performance. This was achieved by modifying the interface defects and matrix porosity, thereby enhancing both the thermoelectric and mechanical properties of the composites. For instance, the addition.

of 2.0 wt% fly ash resulted in a conductivity of 2.17 S/cm, a Seebeck coefficient of 33.75 μV/°C, and a power factor (PF) of 0.2 μW·m⁻¹·K⁻², representing a 2.8-fold increase in the power factor. Similarly, the incorporation of 4.0 wt% silica fume yielded a conductivity of 4.68 S/cm, a Seebeck coefficient of 30.71 μV/°C, a power factor of 0.42 μW·m⁻¹·K⁻², and a ZT value of 2.4 × 10^-5, corresponding to a 6-fold increase in the power factor and a 4.8 fold increase in the ZT value. This research demonstrates a novel approach to leveraging solid waste materials for enhancing the thermoelectric properties of cementitious composites. It not only advances the development of green material technologies but also provides innovative solutions for addressing urban energy and environmental challenges.