Theoretical Investigation of Thermoelectric Properties of Semiconducting Janus \(\hbox {M}_{2}\)COS (M = Zr, Hf) MXenes

A theoretical investigation is conducted on semiconducting MXenes \(\hbox {M}_{2}\)COS (M = Zr, Hf) using both density functional theory and the Boltzmann transport equation. The findings suggest that optimization of thermoelectric properties is more effective through n-type doping than p-type doping. At 300 K, n-type doping yields a power factor of 4.3\(\times \) 10\(^{3}\) \(\mu \)W/\(\hbox {mK}^{2}\) for Zr\({_2}\)COS and 4.5\(\times \) 10\(^{3}\) \(\mu \)W/\(\hbox {mK}^{2}\) for Hf\({_2}\)COS. Furthermore, lattice thermal conductivity (\(\kappa _{l}\)) values of 21.8 W/m K and 27 W/m K are obtained for Zr\({_2}\)COS and Hf\({_2}\)COS, respectively, at 300 K. These values are lower than the lattice thermal conductivity of oxygen-functionalized MXenes \(\hbox {Zr}_2\hbox {CO}_2\) (61.9 W/m K) and \(\hbox {Hf}_2\hbox {CO}_2\) (86.3 W/m K). The projected thermoelectric figure of merit value can potentially reach 0.27 and 0.23 at 700 K for n-type Zr\({_2}\)COS and Hf\({_2}\)COS, respectively. These findings reveal the promising application prospects for n-type Zr\({_2}\)COS and Hf\({_2}\)COS in the field of thermoelectric materials.