Tailoring the Thermoelectric Properties of 3D-Printed n-Type Bi_1.7Sb_0.3Te₃ with Incorporated Edge-Oxidized Graphene

Using three-dimensional (3D) printing technology to fabricate Bi₂Te₃-based thermoelectric (TE) generators opens a potential way to create shape-conformable devices capable of recovering waste heat from thermal energy sources with diverse surface morphologies. However, pores formed in 3D-printed Bi₂Te₃-based materials by the removal of the organic ink binder result in unsatisfactory performance compared to the bulk materials, which has limited the widespread application of the ink-based 3D printing process. Furthermore, managing the volatile Se element in the n-type materials poses significant technological challenges compared to the p-type counterparts, resulting in a scarcity of research on 3D printing of n-type Bi₂Te₃. Here, we synthesized edge-oxidized graphene (EOG)-incorporated Se-free n-type Bi_1.7Sb_0.3Te₃ (BST) using a direct ink writing (DIW) process with a binder-free novel ink. The incorporated EOG provides connectivity between small BST grains separated by pores and induces a bimodal-like grain structure during the DIW and sintering process. The optimal EOG content of 0.1 wt % in 3D-printed n-type BST simultaneously achieved both carrier transport control and active phonon scattering, due to its unique microstructure. A maximum ZT of 0.71 was obtained in the 0.1 wt % EOG/BST materials at 448 K, comparable to commercial bulk n-type Bi₂Te₃-based materials. Further, a single-element device composed of the EOG-BST material exhibited a 2-fold improvement in performance compared to pure-BST. These results open a technological route for the application of 3D printing technology for ink-based TE materials.