Tailoring the Thermoelectric\nProperties of 3D-Printed\nn‑Type Bi<sub>1.7</sub>Sb<sub>0.3</sub>Te<sub>3</sub> with\nIncorporated Edge-Oxidized Graphene

Using three-dimensional (3D) printing technology to fabricate\nBi<sub>2</sub>Te<sub>3</sub>-based thermoelectric (TE) generators\nopens\na potential way to create shape-conformable devices capable of recovering\nwaste heat from thermal energy sources with diverse surface morphologies.\nHowever, pores formed in 3D-printed Bi<sub>2</sub>Te<sub>3</sub>-based\nmaterials by the removal of the organic ink binder result in unsatisfactory\nperformance compared to the bulk materials, which has limited the\nwidespread application of the ink-based 3D printing process. Furthermore,\nmanaging the volatile Se element in the n-type materials poses significant\ntechnological challenges compared to the p-type counterparts, resulting\nin a scarcity of research on 3D printing of n-type Bi<sub>2</sub>Te<sub>3</sub>. Here, we synthesized edge-oxidized graphene (EOG)-incorporated\nSe-free n-type Bi<sub>1.7</sub>Sb<sub>0.3</sub>Te<sub>3</sub> (BST)\nusing a direct ink writing (DIW) process with a binder-free novel\nink. The incorporated EOG provides connectivity between small BST\ngrains separated by pores and induces a bimodal-like grain structure\nduring the DIW and sintering process. The optimal EOG content of 0.1\nwt % in 3D-printed n-type BST simultaneously achieved both carrier\ntransport control and active phonon scattering, due to its unique\nmicrostructure. A maximum <i>ZT</i> of 0.71 was obtained\nin the 0.1 wt % EOG/BST materials at 448 K, comparable to commercial\nbulk n-type Bi<sub>2</sub>Te<sub>3</sub>-based materials. Further,\na single-element device composed of the EOG-BST material exhibited\na 2-fold improvement in performance compared to pure-BST. These results\nopen a technological route for the application of 3D printing technology\nfor ink-based TE materials.