Mesoporous Ag2Se as a model n-type thermoelectric: soft-templated synthesis and thermal transport engineering.

Mesoporous structuring is a promising route to suppress thermal conductivity in thermoelectrics by enhancing phonon scattering, yet mesoporous thermoelectric materials remain scarcely explored. Here, we report the synthesis and thermoelectric evaluation of mesoporous Ag2Se as a model n-type system. Mesoporous Ag2Se thin films are obtained by block-copolymer-directed soft-templated electrodeposition using PS-b-PEO micelles, which interact with Ag+ and Se(iv) species and direct the formation of orthorhombic β-Ag2Se frameworks with a high density of mesopores. By tuning the molecular weight of copolymers and applying an optimized deposition potential of -0.48 V vs. Hg/Hg2SO4 (saturated K2SO4), we realize narrowly distributed pore diameters of 8, 12, and 16 nm and a concomitant deposition in crystallite size. The films are delaminated from ITO substrates and pressed into pellets while preserving both the mesoporous architecture and the β-Ag2Se lattice. For the Ag2Se-12 nm sample, the thermal conductivity at room temperature is reduced from 0.93 W m-1 K-1 for nonporous Ag2Se to 0.40 W m-1 K-1, with moderate degradation of the power factor, resulting in a room-temperature zT of 0.98 (56% enhancement). These results establish mesostructural engineering in Ag2Se as an effective strategy to reduce the thermal conductivity, providing a design principle for next-generation thermoelectrics.