Surface characterization of BiSbTe thermoelectric films electrodeposited from chlorides aqueous solutions and choline chloride based ionic liquids

Investigations of obtaining BiSb, BiTe, SbTe and BiSbTe films in concentrated chloride aqueous solution (5 M NaCl + 1 M HCl) or in ionic liquid based on choline chloride + malonic acid mixture were reported. The concentrations of Bi, Sb, Te, existing as complex anions due to high Cl− concentration, were within 10–90 mM. The measurements were carried out at room temperature for aqueous medium and 85 °C for ionic liquid. Cyclic voltammetry and electrochemical impedance spectroscopy using Pt electrode were used for investigating the interface process in both electrolytes. The morphology and chemical composition of films deposited on Cu in chloride aqueous solution using current pulses or potential pulses were determined by AFM and SEM microscopy. For BiSb, the effects of change from unipolar to reverse pulses and increase in cathodic current were shown as favorable. SEM images for BiSbTe confirmed the morphology modification by increasing the current pulses, while energy dispersive spectroscopy analyses indicate a dramatic change of composition.

Research highlights▶ Electrodeposition of BiSbTe compound using a moderately acid aqueous electrolyte. ▶ The ionic liquid based on choline chloride was useful as electrolysis medium.▶ From CV and EIS it was possible to predict the potential range for deposition.▶ The deposition of BiSbTe from both electrolytes occurs on a Te-covered Pt substrate. ▶ Current and potential pulse plating procedures are effective for obtaining BiSbTe.