Porous Bi ₂ S ₃ Bulk With Excellent Thermoelectric Performance by Solid States Replacement and Low Melting‐Point Metal Volatilization

Bismuth sulfide (Bi₂S₃) exhibits potentials in thermoelectric field, due to their environmental friendliness, high Seebeck coefficients, and low thermal conductivity. However, the peak ZT for binary Bi₂S₃ does not exceed 1.0, inhibiting its practical applications. Starting from the precipitation smelting of bismuth concentrate process, this study constructs multi-type, multi-scale in-situ secondary phases and porous structures through FeCoNi (FCN) medium-entropy alloy addition, significantly enhancing the ZT value of Bi₂S₃-based thermoelectric materials. The introduced FCN reacts with pre-synthesized Bi₂S₃ nanorod matrix during spark plasma sintering and forms precipitate complex with FCN-S core and Bi shell microstructures. FCN doping improves the carrier concentration of Bi₂S₃ and the reduced Bi from Bi₂S₃ acts as carrier transport channels for mobility optimization. Due to the stacking effect of Bi₂S₃ nanorods and the volatile nature of metallic Bi, porous Bi₂S₃ structure is formed, characterized by randomly-distributed and micro-to-nanoscale pores. The coexistence of various lattice defects effectively scatter phonons and suppress the lattice thermal conductivity, thus an excellent peak ZT of 1.1 is achieved at 773 K in a 0.25 wt.% FCN-doped Bi₂S₃ sample. This study, drawing on the process of ore smelting, proposes a convenient method for preparing high-performance chalcogenide thermoelectric materials with porous structures.