Enhancement of thermoelectric performance of NaxCo2O4 with Ag dispersion by precipitation from Ag+ aqueous solution

Abstract

Thermoelectric NaxCo2O4/Ag composites were synthesized by citric acid complex (CAC) method and Ag precipitation from CH3COOAg aqueous solution on the NaxCo2O4 powders. Effects of the synthesis process on microstructure and thermoelectric performance of NaxCo2O4/Ag composites were investigated. When the NaxCo2O4 CAC powders were dipped in CH3COOAg aqueous solution and dried, fine Ag particles less than around 300 nm in size were precipitated on the surface of NaxCo2O4 powders. After the subsequent sintering process, the flaky Ag phase, the length and thickness of which were up to 5 and 1 μm, respectively, existed along interfaces between NaxCo2O4 grains. The sizes of Ag particles obtained in this study were found to be smaller than those of the conventionally prepared NaxCo2O4/Ag composites. The fine dispersion of Ag grains was effective for suppressing the increase in thermal conductivity due to the addition of metallic phase, Ag, and for improving the thermoelectric performance of NaxCo2O4/Ag composites, suggesting that the synthesis technique composed of the CAC method and Ag precipitation from CH3COOAg aqueous solution is significantly important process for thermoelectric NaxCo2O4/Ag composites.