Use of a Soluble Anode in Electrodeposition of Thick Bismuth Telluride Layers

Abstract

International audienceIntegration of thermoelectric devices within an automotive heat exchanger could enable conversion of lost heat into electrical energy, contributing to improved total output from the engine. For this purpose, synthesis of thick bismuth telluride (Bi2Te3) films is required. Bismuth telluride has been produced by an electrochemical method in nitric acid with a sacrificial bismuth telluride anode as the source of cations. The binary layer grows on the working electrode while the counter-electrode, a Bi2Te3 disk obtained by high frequency melting, is oxidized to Bi-III and Te-IV. This process leads to auto-regeneration of the solution without modification of its composition. The thickness of films deposited by use of the Bi2Te3 anode was approximately 10 times that without. To demonstrate the utility of a soluble anode in electrochemical deposition, we report characterization of the composition and morphology of the films obtained under different experimental conditions. Perfectly dense and regular Bi2Te3 films (similar to 400 mu m) with low internal stress and uniform composition across the cross-section were prepared. Their thermoelectric properties were assessed

Electrochemical deposition of bismuth telluride thick layers onto nickel

“…Backscattering SEM images as shown in Figure 3 corresponding to basal planes perpendicular to the substrate [8,9] which coincides with the preferential orientation of films exhibiting the best thermoelectric performance. …”

“…To achieve the growth of Bi 2 Te 3 thick films a number of strategies have been employed which include the use of pulsed electrodeposition [8] and the use of a soluble Bi 2 Te 3 anode [9].…”

Synthesis and Evaluation of Thick Films of Electrochemically Deposited Bi2Te3 and Sb2Te3 Thermoelectric Materials

“…These layers become unstable as the layer thickness increases. For this reason, only a small number of studies have been successful in synthesizing thick films of BiTe and SbTe [3,14,15,16,21]. As shown in Figure 8a, although a 200-µm-thick film can be grown using the constant method at a high deposition rate of approximately 30 µm/h, only 20 µm of the thickness is actually of good quality (Figure 8b).…”

“…Many non-aqueous additives have been researched for Bi 2 Te 3 : ethylene glycol [ 6 , 7 ] dimethyl sulfoxide [ 8 , 9 ], ethanol [ 10 ], ionic liquids (choline chloride) [ 11 , 12 ], molten salt (AlCl 3 –NaCl–KCl) [ 13 ], and polyvinyl alcohol [ 14 ]. Additionally, the appearance of the Bi 2 Te 3 soluble anode is proven to enhance a homogeneous composition of deposited films in References [ 14 , 15 , 16 ]. In this work, another possibility of a deposition of thick and stable thermoelectric films has been demonstrated.…”

“…Therefore, the amorphous material is easily crystallized during the pulsed deposition. By this method, without the necessity of using non-aqueous additives and a soluble anode, the Seebeck coefficients of synthesized Bi 2 Te 3 thick films are more improved than that of using high concentration electrolytes [ 5 ], and the same as using a soluble anode (~−80 µV/K) [ 15 , 16 ]. Additionally, this mechanism is successfully applied for not only N-type Bi 2 Te 3 but also P-type Sb 2 Te 3 thick films.…”