Boosting High Thermoelectric Performance of Ni-Doped CuS by Significantly Reducing Thermal Conductivity.

At present, copper sulfide materials have been predicted as promising thermoelectric materials due to their inexpensiveness and nontoxicity property. Most researches on copper sulfide are focused on CuS and CuS because they are more easily synthesized into a single phase; however, the improper electrical conductivity greatly hindered their thermoelectric properties. In this work, a series of high-performance CuNiS ( = 0, 0.01, 0.015, and 0.02) bulk samples were fabricated by accurately manipulating the ratio of Cu/S with appropriate Ni-doping. The thermoelectric properties of Ni-doped CuS were explored in detail for the first time. It can be found that carrier thermal conductivity and lattice thermal conductivity of CuNiS were effectively reduced via Ni-doping, simultaneously, without the great influence on the power factor. Here, the carrier thermal conductivity (κ) was reduced due to the extreme reduction of Hall carrier concentration. In addition, amounts of nanopores introduced by Ni-doping and complex crystal structure from the phase transition of the second phase strengthen the phonon scattering and reduce lattice thermal conductivity (κ) remarkably. As a consequence, the lowest carrier thermal conductivity and lattice thermal conductivity reach 0.006 and 1.08 W m K for CuNiS at 773 K, and the average ZT is about 0.39 from 323 to 773 K (the ZT is about 0.9 at 773 K). This work demonstrates that low-cost and easily fabricated Ni-doped CuS is a pleasurable candidate for thermoelectric application despite it usually being treated as an ion conductor.