Graphite Nanosheets as Multifunctional Nanoinclusions to Boost the Thermoelectric Performance of the Shear-Exfoliated Bi₂O₂Se

As an eco-friendly oxide-based thermoelectric material, Bi₂O₂Se exhibits considerable potential for practical device application, but its low electrical conductivity needs to be further improved to achieve higher thermoelectric performance. Here, a record-high figure of merit, ZT of >0.7 at 773 K in the shear-exfoliated nanostructured Bi₂O₂Se with graphite nanosheets as multifunctional secondary nanoinclusions, is achieved. The introduced graphite nanosheets regularize the arrangement of Bi₂O₂Se nanograins, strengthen the anisotropy, and act as the “expressway” to improve the electrical conductivity by simultaneously enhancing the electron carrier concentration and mobility of the hybrid materials, leading to a high power factor of ≈6.0 µW cm^–1 K^–2 at 773 K. Also, the liquid-phase shear exfoliation refines both graphite and Bi₂O₂Se into nanosheets. Moreover, the as-sintered hybrid bulk materials composed of these nanosheets possess dense grain and phase boundaries, as well as various lattice imperfections, such as lattice distortions and stacking faults formed by physical shearing, which can significantly scatter the phonons with different wavelengths and in turn contribute to a low thermal conductivity of only 0.63 W m^–1 K^–1 at 773 K, both contributing to a competitive ZT of ≈0.73 at this temperature, indicating the great potential for practical applications.