Cathodic Behaviors On The Electro-deposition Of PbTe In Pb（NO₃）₂-TeO₂-NaOH Solution

As a kind of function material, thermoelectric materials, which has wide application prospect in space, optoelectronics, and medical biology area for its safety, reliability, no pollution, and no noise in aspect of power generation and cooling, can alternate heat energy and electric energy each other. Lead telluride (PbTe) is a kind of thermoelectric materials, and is used in practice at high temperature of500-800K since it has high melting point, isotropic and symmetrical structure, and low thermal conductivity. By conducting a review on thermoelectric materials and the elemental doping of PbTe for property improvement, it is supposed that electro-deposition process can be used to produce PbTe based thin film materials with various doping elements. More important, the investigation of the cathodic behavior can help to prepare the good quality PbTe based materials.Cyclic voltammetry, linear sweep voltammetry, galvanostatic potentiometry (interval time<011.ls) and amperometry (interval time<0.1s) were performed respectively in the solution of Pb(NO3)2-NaOH, TeO2-NaOH and Pb(NO3)2-TeO2-NaOH. And copper, graphite and Hg/HgO were selected as working electrode, counter electrode and reference electrode. Some conclusions were summarized as follows:(1) In5mMPb(NO3)2-100mM NaOH system, the study of cyclic voltammogram shows that the cathode electrochemical reduction started at the potential of-0.45V (vs.Hg/HgO), and this behavior was a one-step reaction with2electrons transfer:Pb2++2e-=Pb. Cathode reduction process was quasi-reversible. The electro-deposition process is diffusion-control and instantaneous nucleation model. The E-pH diagram of Pb-Na-H2O system drawn through thermodynamic analysis and calculation shows that the potential of deposition of Pb ranges from-0.3V to-2.7V(vs.Hg/HgO). Homogeneous Pb coating could be obtained at potential of-0.7V by galvanostatic potentiometry.(2) In the solution of10mMTeO2-100mMNaOH, four reduction peaks appear in cyclic voltammogram curves, and their starting potential are-0.46V,-0.82V,-1.3V and-1.5V, and their reduction peaks are-0.63V,-0.98V,-1.47V and-1.8V, respectively. And these potentials corresponded to the reactions as Te4++2e-=Te2+, Te2++2e-=Te, Te+2e-=Te2-, and2H2O+4e-=H2+2OH-. Electrode-deposition reaction of Te2++2e=Te is diffusion-control process, and the electrochemical reduction of Te2++2e-=Te on copper electrode is progressive nucleation model. Homogeneous Te coating could be seen at potential of-0.9V by galvanostatic potentiometry.(3)Five reduction peaks, which are assigned as Te4+â†'Te2+, Pb2+â†'Pb, Te2+â†'Te, Teâ†'Te2-,and H+â†'H2respectively, were found on the CV curve of10mM TeO2-5mM Pb(NO3)2-200mM NaOH. PbTe can be deposited electrochemically in the solution, and the electro-deposition process of PbTe is diffusion-control. The electrochemical reduction mechanism of PbTe was complicated for the effect of nucleation mechanism of Pb deposition and Te deposition. Using several analysis, such as electrolyzing at different potentials, calculation of electrode potential of electrochemical reaction and the E-pH diagram of Pb-Te-Na-H2O, we come to a conclusion that the reaction of Pb+TeO32-+3H2O+4-4e-=PbTe+6OH-is the formation mechanism of PbTe. In addition, a pure PbTe coating was obtained by electro-deposition at-1.1V for2000seconds, and atomic ratio of Pb to Te in the coating deposited electrochemically at-1.0V was close to1:1.