Incorporation of MXene into Bi₂S₃ Matrix Promotes Better Electron Transport and Enhanced Thermoelectric Figure of Merit

Contrary to the state-of-the-art thermoelectrics, such as tellurides and selenides, the thermoelectric performance of earth-abundant and less toxic Bi2S3 has been found to be inferior primarily because of poor electron transport. Herein, a less explored approach of composite formation using nanoinclusions of two-dimensional (2D) MXene, a graphene-analogous material, in Bi2S3 has been adopted to tailor the transport properties in order to obtain enhanced thermoelectric figure of merit (ZT). Highly conductive stacked sheets of Ti3C2TX MXene, incorporated into the matrix of Bi2S3, facilitate smoother electron transport, resulting in significantly enhanced electrical conductivity. A remarkable 745% upsurge in electrical conductivity is found in a Bi2S3 + 1 wt % Ti3C2TX MXene composite compared to pristine Bi2S3. Interestingly, temperature-dependent thermal conductivity shows a steep decline trend in these composites. More than 50% falloff in lattice thermal conductivity at 710 K from 375 K is observed for the 1 wt % MXene-added Bi2S3 composite. Further, the Debye-Callaway model fitting suggests an order of magnitude increase in phonon-phonon Umklapp scattering induced in MXene-incorporated Bi2S3 composites. Synergistic improvement of electron transport along with enhanced phonon scattering, especially at high temperatures, results in 2.69 times improved ZT at 710 K. Further, MXene addition causes much improved mechanical strength in otherwise brittle Bi2S3. Our results suggest that a composite route using MXene can be an effective strategy for developing a low-cost, earth-abundant, sulfide-based thermoelectric power generator.