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Thermoelectric materials can be used to convert waste heat into electrical energy, which is considered to be a cleaner form of energy that reduces carbon dioxide and greenhouse gas emissions. In this work, we study the thermoelectric properties of penta-PdX2 (X = S, Se, Te) using first-principles calculations together with Boltzmann transport theory. The dynamic and thermal stability of penta-PdX2 is confirmed based on phonon dispersion and ab initio molecular dynamics (AIMD) simulations. The transport coefficients, such as thermal conductivity (kl), power factor (PF) and thermoelectric figure of merit (ZT), exhibit strong anisotropy in both x and y directions. The lower thermal conductivity of penta-PdX2 can be attributed to the lower group velocity and larger phase space. The thermal conductivity of penta-PdX2 along the same direction (x or y direction) adheres to the trend of PdS2 ＞ PdSe2 ＞ PdTe2. The anisotropy of PF and kl of penta-PdX2 monolayers inevitably leads to anisotropy of ZT. The largest ZT values of penta-PdX2 (X = S, Se) for p-type are 0.85 and 1.18, respectively, while the maximum ZT value of penta-PdTe2 reaches 2.42. The predicted ZT values of penta-PdX2 are larger than those of the commercial TE material Bi2Te3 (about 0.8) and some other transition metal di-chalcogenides, indicating that penta-PdX2 (X = S, Se, Te) monolayers are potential anisotropic thermoelectric materials. [ABSTRACT FROM AUTHOR]

In the original publication of this article, acknowledgement disclaimer was not published completely. [ABSTRACT FROM AUTHOR]

Strain engineering can effectively improve the energy band degeneracy of two-dimensional transition metal dichalcogenides so that they exhibit good thermoelectric properties under strain. In this work, we have studied the phonon, electronic, thermal, and thermoelectric properties of 1T-phase monolayer HfS 2 with biaxial strain based on first-principles calculations combined with Boltzmann equations. At 0% strain, the results show that the lattice thermal conductivity of monolayer HfS 2 is 5.01 W m -1 K -1 and the electronic thermal conductivities of n-type and p-type doped monolayer HfS 2 are 2.94 and 0.39 W m -1 K -1 , respectively, when the doping concentration is around 5 × 10 12 cm -2 . The power factors of the n-type and p-type doped monolayer HfS 2 are different, 29.4 and 1.6 mW mK -2 , respectively. Finally, the maximum ZT value of the n-type monolayer HfS 2 is 1.09, which is higher than 0.09 of the p-type monolayer HfS 2 . Under biaxial strain, for n-type HfS 2 , the lattice thermal conductivity, the electronic thermal conductivity, and the power factor are 1.55 W m -1 K -1 , 1.44 W m -1 K -1 , and 22.9 mW mK -2 at 6% strain, respectively. Based on the above factor, the ZT value reaches its maximum of 2.29 at 6% strain. For p-type HfS 2 , the lattice thermal conductivity and the electronic thermal conductivity are 1.12 and 1.53 W m -1 K -1 at 7% strain, respectively. Moreover, the power factor is greatly improved to 29.5 mW mK -2 . Finally, the maximum ZT value of the p-type monolayer HfS 2 is 3.35 at 7% strain. It is obvious that strain can greatly improve the thermoelectric performance of monolayer HfS 2 , especially for p-type HfS 2 . We hope that the research results can provide data references for future experimental exploration., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)