纳米TiO2薄膜电极的电化学方面的初步研究/THE STUDY OF ELECTROCHEMICAL TEST ON NANO-TIO2 FILM ELECTR
TiO2 nano-semiconductor film electrodes were prepared by chemical thermal decomposition method, and electrochemical technique was adopted to study the electrodes. The attribution of electrode reactions in 3.5%NaCl aqueous solution, the electrode reaction kinetics, and the band structure of the nano-TiO2 were explored.
Weighing test verifies that the films on the electrodes do not erode or exfoliate in the electrochemical test system. TEM micrograph indicates that the grain size of TiO2 on the electrodes is controlled at about 20nm.
UV-vis spectroscopy was employed to learn the spectral absorption properties of the TiO2 on the electrodes; it was found that the material has strong absorption in UV region, and still has obvious absorption in visible and near-infrared region.
A reference for cyclic voltammetry (CV) was established. In the potential range of -1.8V~-0.9697V, there is an oxidation reaction on CV curve which corresponds to the oxidation of trivalent titanium compound to tetravalent titanium oxide. The second oxidation peak on CV curve indicates the generation of hydroxyl radicals (•OH), which were excited by polarization potential, and the minimum polarization potential should meet ΔEOH-/•OH>+1.453V. CV curve also indicates the generation of superoxide anion radicals. Both the occurrences of hydroxyl radicals and superoxide radicals were verified by electron spin resonance (ESR) test. Looking into the relationship between peak current and the square root of scan speed, it was found that the reaction of trivalent titanium compound to tetravalent titanium oxide and the reaction of •OH generation are both controlled by diffusion step.
By analyzing Mott-Schottky curve, we learned that the flat band potential of the film electrode is -0.67V and the doping concentration is 2.870×1017 cm3.
Extensive researches with respect to the film electrodes were done further by electrochemical impedance spectroscopy (EIS). The Nyquist graphs show that the electrode reaction is controlled by the diffusion of charged ions at the potential range of -1.2V, -0.9V and -0.6V, and the migration rate of charged ions is minimum at the potential range of -0.3V, 0.0V and +0.3V. The results also indicate that the activity of •OH generation rises as the electrode potential increases, agreeing well with the results of cyclic voltammetry. Fitting the EIS graphs, we know the equivalent circuit of the electrodes at about -0.9V is RS(Q1R1(Q2R2)), the equivalent circuit at about 0.0V is RS(QR1), and the equivalent circuit at the potentials corresponding to the generation of •OH is RS(Q1R1)(Q2R2).