Thermoelectric properties of cement composite analogues from first principles calculations

Buildings are responsible for a considerable fraction of the energy wasted globally every year, and as a result, excess carbon emissions. While heat is lost directly in colder months and climates, resulting in increased heating loads, in hot climates cooling and ventilation is required. One avenue towards improving the energy efficiency of buildings is to integrate thermoelectric devices and materials within the fabric of the building to exploit the temperature gradient between the inside and outside to do useful work. Cement-based materials are ubiquitous in modern buildings and present an interesting opportunity to be functionalised. We present a systematic investigation of the electronic transport coefficients relevant to the thermoelectric materials of the calcium silicate hydrate (C-S-H) gel analogue, tobermorite, using Density Functional Theory calculations with the Boltzmann transport method. The calculated values of the Seebeck coefficient are within the typical magnitude (200 - 600 $\mu V/K$) indicative of a good thermoelectric material. The tobermorite models are predicted to be intrinsically $p$-type thermoelectric material because of the presence of large concentration of the Si-O tetrahedra sites. The calculated electronic $ZT$ for the tobermorite models have their optimal values of 0.983 at (400 $\mathrm{K}$ and $10^{17}$ $\mathrm{cm^{-3}}$) for tobermorite 9 \r{A}, 0.985 at (400 $\mathrm{K}$ and $10^{17}$ $\mathrm{cm^{-3}}$) for tobermorite 11 \r{A} and 1.20 at (225 $\mathrm{K}$ and $10^{19}$ $\mathrm{cm^{-3}}$) for tobermorite 14 \r{A}, respectively.