For the first time, the thermoelectric properties of cement/single-walled carbon nanotube (SWCNT) nanocomposites with over 3, 7, 14 and 28 days of hydration are reported, while a thermoelectric generator device (TEG) is fabricated utilising the material with the highest achieved power factor (PF). SWCNTs with inherent p-type semiconductor characteristics were introduced into the cementitious matrix at a water to cement (w/c) ratio of 0.5, while the Seebeck coefficient (S), electrical conductivity (σ) and PF for different SWCNT loadings were determined at different ages. The 28 day cement/SWCNT sample with 0.5 wt% loading exhibited the highest performance in terms of σ (1.59 × 10³ S m⁻¹), S (+ 1348.8 μV K⁻¹) and PF (2.89 × 10³ μW m⁻¹ K⁻²), with the PF being the highest among other carbon nanoadditive-based cement thermoelectric nanocomposites to date. The cement/SWCNT(0.5) was used for the fabrication of a thermoelectric generator (TEG) device exhibiting a maximum power output (P_max) of 5.02 μW and a power density of 5.02 mW m⁻², upon being exposed to a temperature difference (ΔT) of 50 K. Finite element (FE) simulations validated the TEG thermoelectric performance corroborating the experimental findings. The highly efficient cement/SWCNT thermoelectric nanocomposites, as well as the cement-based structural TEG device, demonstrated herein could open new avenues towards future energy efficient buildings and green construction.

A waste-originated one-part alkali-activated nanocomposite is introduced herein as a novel thermoelectric material. For this purpose, single-walled carbon nanotubes (SWCNTs) were utilized as nanoinclusions to create an electrically conductive network within the investigated alkali-activated construction material. Thermoelectric and microstructure characteristics of SWCNT-alkali-activated nanocomposites were assessed after 28 days. Nanocomposites with 1.0 wt.% SWCNTs exhibited a multifunctional behavior, a combination of structural load-bearing, electrical conductivity, and thermoelectric response. These nanocomposites (1.0 wt.%) achieved the highest thermoelectric performance in terms of power factor (PF), compared to the lower SWCNTs’ incorporations, namely 0.1 and 0.5 wt.%. The measured electrical conductivity (σ) and Seebeck coefficient (S) were 1660 S·m⁻¹ and 15.8 µV·K⁻¹, respectively, which led to a power factor of 0.414 μW·m⁻¹·K⁻². Consequently, they have been utilized as the building block of a thermoelectric generator (TEG) device, which demonstrated a maximum power output (P_out) of 0.695 µW, with a power density (PD) of 372 nW·m⁻², upon exposure to a temperature gradient of 60 K. The presented SWCNT-alkali-activated nanocomposites could establish the pathway towards waste thermal energy harvesting and future sustainable civil engineering structures.

So far, there is no validated technology for characterizing the dispersion and morphology state of carbon nanotubes (CNTs) aqueous dispersions during sonication. Taking advantage of the conductive nature of CNTs, the main hypothesis of the current study is that Electrochemical Impedance Spectroscopy (EIS) is an appropriate technique for the in-situ monitoring and qualification of the dispersion state of CNTs in aqueous media. To confirm our hypothesis, we monitored the Impedance |Z| during the sonication process as a function of type CNTs/admixtures used for the preparation of the aqueous solutions and of crucial process parameters, such as the applied sonication power and duration (i.e., sonication energy). For dispersions above the percolation threshold, a drop of |Z| by approximately seven orders of magnitude was observed, followed by a linear reduction. The dramatic change in |Z| is regarded as an indication of the formation of a conductive path or destruction of an existing one during sonication and can be used to characterize the dispersion and morphology state of CNTs. The results of the EIS provide, straightforwardly and reliably, the required information to create an optimum dispersion protocol for conductive CNT suspensions. The produced dispersions are part of research focusing on the manufacturing of cement-based composite materials with advanced thermoelectric functionalities for energy harvesting. Such dispersions are not only limited to energy harvesting applications but also to applications where functionalities are introduced through the use of conductive-based suspensions.