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

A theoretical investigation is conducted on semiconducting MXenes \(\hbox {M}_{2}\) ${\text{M}}_2$ 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 \(\times \) $\times$ 10 \(^{3}\) $_{}^3$ \(\mu \) $\mu$ W/ \(\hbox {mK}^{2}\) ${\text{mK}}^2$ for Zr \({_2}\) $_2^{}$ COS and 4.5 \(\times \) $\times$ 10 \(^{3}\) $_{}^3$ \(\mu \) $\mu$ W/ \(\hbox {mK}^{2}\) ${\text{mK}}^2$ for Hf \({_2}\) $_2^{}$ COS. Furthermore, lattice thermal conductivity ( \(\kappa _{l}\) ${\kappa }_l$ ) values of 21.8 W/m K and 27 W/m K are obtained for Zr \({_2}\) $_2^{}$ COS and Hf \({_2}\) $_2^{}$ COS, respectively, at 300 K. These values are lower than the lattice thermal conductivity of oxygen-functionalized MXenes \(\hbox {Zr}_2\hbox {CO}_2\) ${\text{Zr}}_2{\text{CO}}_2$ (61.9 W/m K) and \(\hbox {Hf}_2\hbox {CO}_2\) ${\text{Hf}}_2{\text{CO}}_2$ (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 \({_2}\) $_2^{}$ COS and Hf \({_2}\) $_2^{}$ COS, respectively. These findings reveal the promising application prospects for n-type Zr \({_2}\) $_2^{}$ COS and Hf \({_2}\) $_2^{}$ COS in the field of thermoelectric materials.