GGBF slag-based geopolymer for ionic thermoelectric energy harvesting

Geopolymers have emerged as promising materials for various applications, including thermoelectric power generation. In this study, GGBF slag-based geopolymer samples were prepared with varying ratios of alkaline solution (AS) to aluminosilicate source: GGBF slag (S), with AS/S ratios of 0.3, 0.4, and 0.45. The aim was to explore the relationship between thermoelectric properties and the amount of alkaline solution used. Comprehensive measurements of electrical conductivity and the Seebeck coefficient were performed on samples with different AS/S ratios. The reactivity of the samples was monitored using isothermal conduction calorimetry and ultrasonic pulse velocity (UPV) to track the velocity changes in the geopolymer matrix. Furthermore, mechanical properties were assessed through elastic modulus measurements, and microstructural characterization was performed using X-ray diffraction (XRD). The results underscore the influence of the alkaline solution quantity, temperature, and ionic movement on the thermoelectric performance of these materials. Electrical conductivity analysis revealed that ions within the geopolymer matrix play a key role in enhancing charge transport. These findings deepen our understanding of how the alkaline solution affects thermoelectric mechanisms in geopolymers and pave the way for the development of innovative building materials with energy conversion capabilities, offering sustainable solutions for future technologies. • Ground granulated blast furnace (GGBF) slag–based geopolymers were synthesized with varying AS/S ratios (0.30, 0.40, 0.45). • Thermoelectric behavior was evaluated through combined electrical conductivity and Seebeck coefficient measurements. • Reactivity and matrix evolution were monitored using isothermal calorimetry and ultrasonic pulse velocity. • The alkaline solution content strongly influences ionic mobility, matrix formation, and overall thermoelectric performance. • The intrinsic voltage plays a decisive role in governing the apparent thermoelectric efficiency of alkali-activated geopolymers