Record high thermoelectric performance of expanded graphite/carbon fiber cement composites enhanced by ionic liquid 1-butyl-3-methylimidazolium bromide for building energy harvesting

Abstract

The expanded graphite/carbon fiber-reinforced cement composite (EGCFRC) is a new type of intelligent structural material that can directly transform thermal energy into electric energy for large-scale energy harvesting in urban areas and roads. Although using cement composites can harvest energy widely, there is also the big challenge of increasing thermoelectric properties. In this work, the thermoelectric properties of cement composites significantly increased by introducing the ionic liquid 1-butyl-3-methylimidazolium bromide (IL [Bmim]Br) into composite interfaces. The absolute value of the EGCFRC-Seebeck coefficient increased greatly with increasing [Bmim]Br content while keeping a relatively higher electrical conductivity. The modified EGCFRC demonstrated the highest power factor value (94.3 μW m⁻¹ K⁻²) and dimensionless figure of merit (ZT) value (2.208 × 10⁻³) when filled with 3 wt% IL [Bmim]Br. The durability of EGCFRC was also evaluated and the maximum absolute Seebeck coefficient value (746 μV K⁻¹) was obtained after 10 freezing–thawing cycles at 80 °C. The enhanced mechanism of [Bmim]Br on thermoelectric properties was carefully investigated and attributed mainly to the migration and rearrangement of the anions and cations of [Bmim]Br in composite interfaces.