Aqueous electrodeposition of cobalt-antimony films and nanowires for thermoelectric applications

Solid-state thermoelectric devices may be used for refrigeration or to convert waste heat into electricity, but they are limited by their high cost and relatively low efficiency as compared to conventional systems. Their efficiency has recently been improved through advances in the materials science and chemistry of thermoelectric materials, including nanostructuring. The work reported herein was focused on developing an aqueous electrochemical fabrication route to the formation nanowire of one thermoelectric material, cobalt triantimonide (CoSb3).;Potential-pH (E-pH or Pourbaix) and speciation diagrams are constructed for the cobalt-water, antimony-water, and cobalt-antimony-water systems with and without the additional complexing ligands acetate, fluoride, and tartrate using thermodynamic values derived from recent literature. The results of these calculations are evaluated against the observed UV-vis absorption behavior to highlight gaps in the collective knowledge of these systems. The calculations predict that the direct electrodeposition of cobalt triantimonide is possible from aqueous solutions containing fluoride or tartrate, but that the deposition may compete with that of antimony, cobalt diantimonide, and cobalt antimonide, with the most energetically favorable reduction product dependent upon solution acidity and the relative activities of the precursor ions.;Three electrolytes containing cobalt(II), antimony(III), tartrate, and chloride and/or acetate were developed. Potentiostatic depositions of both films and nanowires (the latter included the use of porous anodic alumina templates) were made from these electrolytes as well as a fourth electrolyte reported in the literature. The deposits were inspected by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometry (EDS). Based on the chemical composition of the deposits, the most successful electrolytes contained a 10:1 atomic ratio of cobalt(II) to antimony(III). However, the inter- and intrasample variability of the chemical composition of the deposits was found to be too great for practical applications.