High-ion-conductive zeolite X with built-in < 1 nm 3D pores achieving superior thermoelectric performance

The complex coupling between thermoelectric parameters makes it extremely challenging to improve the performance of materials. Typically, the reduction of thermal conductivity by incorporating porous structures often leads to a compromise in electrical conductivity. Herein, we present high-ion-conductive zeolite X (including Na-, Ca-, and Li-low silica type-X (LSX)) as the subnanoporous additive in the Bi_0.4Sb_1.6Te₃ (BST) matrix. Owing to the high pore charge density of zeolite X, the decrease in conductivity is effectively suppressed while maintaining a low thermal conductivity. Positively charged metal cation (M⁺) and valence electron of oxygen atom in aluminum-oxide tetrahedron of zeolite X achieve charge balance. Cationic with different electronegativity regulated electrons of oxygen atom transferred from the oxygen atoms to the BST matrix. The lower electronegativity of Na⁺ leads to a higher electron density surrounding oxygen atoms in Na-LSX. Thus, more electrons are transferred to the BST matrix from the oxygen atoms in Na-LSX and form Te–O bonds. Ultimately, the figure-of-merit (ZT) peak of BST/0.8 wt.% Na-LSX nanocomposites reached 1.47 at 373 K, with a huge cooling temperature difference of 69.4 K and an excellent thermoelectric conversion efficiency of 6.95%. This work exploits the stable and unique three-dimensional pore structure of X-type molecular sieves, broadening their potential application in the thermoelectric medium temperature range.