Incorporation of MXene into BiS 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 BiS 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 BiS has been adopted to tailor the transport properties in order to obtain enhanced thermoelectric figure of merit (). Highly conductive stacked sheets of TiCT MXene, incorporated into the matrix of BiS, facilitate smoother electron transport, resulting in significantly enhanced electrical conductivity. A remarkable 745% upsurge in electrical conductivity is found in a BiS + 1 wt % TiCT MXene composite compared to pristine BiS. 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 BiS composite. Further, the Debye-Callaway model fitting suggests an order of magnitude increase in phonon-phonon Umklapp scattering induced in MXene-incorporated BiS composites. Synergistic improvement of electron transport along with enhanced phonon scattering, especially at high temperatures, results in 2.69 times improved at 710 K. Further, MXene addition causes much improved mechanical strength in otherwise brittle BiS. 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.