Study On Formation And Effects Mechanism Of Solid Solution In Ti/SnO₂-SbO_x Electrode

Titanium anodes application in electrochemical industry, such as electrochemical synthesis and the degradation of pollutant is very promising. However, the disadvantage is that the evolving oxygen diffusing into the substrate to form titanium dioxide-an insulator-can cause a reduction of conductivity and weakening the binding of activated layer to the substrate, the former will detach from the titanium support, especially in a strong acid electrolyte. Addition of oxides as an intermediate layer interposed between substrate and activated layer, all form of a solid solution, provides a way to improve corrosion resistance, binding force and conductivity. Among the intermediate layers, Sb doped SnO₂ solid solution is an effective component which can enhance the stability and conductivity of electrodes. However, the formation and effects mechanism of solid solution on the performance of electrode has been rarely studied, so the theory has lagged behind and hindered titanium anodes further development.This paper presents an investigation on formation and effects mechanism of solid solution in electrode, the SnO₂-SbO_x was chose as the representative solid solution materials. Firstly, the prepared electrodes were characterized, solid solution formation mechanism was discussed, the crystal structure, surface morphology, voltammetric charge was researched using TG/DTA,XRD,XPS,SEM,CV methods. Secondly, the fractal geometry theory was introduced into the area of titanium electrodes, electrodes fractal dimensions were calculated by mass-radius, box counting, and cyclic voltammetry methods. The correlation between surface fractal dimension and the electrode electro-performance was proposed. Thirdly, the stability of solid solution was studied based on the theory of doping and defects in semiconductor and crystal theory combined with experimental data. Fourthly, anodes deactivation mechanism was discussed by CV and EIS methods. Finally, the crystal lattice parameters, energy band structure, density of state of SnO₂-SbO_x solid solution were calculated by First-principles method. The conclusions are as follows:1. Solid solution can form at 440℃, the formation mechanism is Thesurface of solid solution electrode is rough and porous, the inner surface area possesses about 80 to 95 percent of the total. The growth activation energy of solid solution is low (12.63 kJ/mol) due to the effect of oxygen vacancies. The lowest fractal dimensions of the most stable electrode sintered at 450℃with 4 at% Sb doping is 1.42 and 1.57 for mass -radius and box-counting methods respectively. The electrode fractal dimensions calculated from cyclic voltammetry under different sintering temperatures agree well with the results of voltammetric charges. The fractal dimension of electrodes with different Sb doping ratios is coinciding with the results of surface morphology.2. The theoretical stable Sb doping ratios for sintered SnO₂-SbO_x solid solution electrodes is 4-7 at%, the experimental results is 3.2-5.8 at%. The longest service life of electrode can reach 30 h under accelerated life test.3. The deactivation mechanism for solid solution electrodes is due to the combination of TiO₂ inner layer deactivation and SnO₂ outer layer deactivation. Outer layer deactivation occurs earlier than inner layer deactivation.4. Two stability mechanism of TiO₂-SnO2 were proposed, one may due to the increase of E_g leading to low combination rate of electrons and vacancies for Ti_1-xSn_xO₂ and the decrease of E_g leading to an easier electron transition for Sn_1-xTi_xO₂.The other is the electrons in conduction band moving to higher energy leading to a more powerful O₂ reduction ability. The crystal lattice parameters of solid solution firstly increase then decrease with the increase of Sb doping amounts. It is proved that there is equilibrium between Sb³⁺ and Sb⁵⁺. The Fermi level can move into the conduction band, which will leads to a higher conductivity, however, the heavy doping will lead to the conductivity deterioration due to the divergence of donor level E_d from conduction band.