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

2018-11-21 09:05:21

电极 potential TiO2 电位 electrodes



本文采用化学热分解法制备了纳米TiO2薄膜电极,并利用电化学方法对电极在3.5%NaCl溶液中的电极反应的类型、电极反应动力学以及能带结构进行研究。
通过称重试验验证了电极在溶液中不发生腐蚀、脱落的情况。采用TEM电镜发现电极材料的晶粒尺寸基本在20nm左右。
利用紫外-可见吸收光谱分析纳米TiO2薄膜电极在光谱范围内的吸收情况,发现纳米TiO2薄膜电极材料在紫外光区范围内有很强的吸收另外在可见和红外光区也有明显的吸收。
建立电化学势窗,采用循环伏安法得到在-1.8V~ -0.9697V电位范围的出现三价钛化合物转化成四价钛氧化物的氧化反应;第二个氧化峰是羟基自由基产生的信号,它的产生是由于电位的极化,其最小激发电位满足ΔEOH-/•OH>+1.453V。另外通过•OH的ESR测试验证了羟基自由基的产生。循环伏安曲线上还有超氧阴离子自由基产生的信号。另外通过不同电位扫描速度下的循环伏安曲线峰值电流比较,断定三价钛化合物转化成四价钛氧化物的氧化反应和羟基自由基产生的电极反应都是由扩散步骤控制的。
分析Mott-Schottky曲线得到纳米TiO2薄膜电极的平带电位为-0.67V,掺杂浓度ND为2.870×1017个/cm3。
根据交流阻抗Nyquist图可知,在电极电位为-1.2V、-0.9V和-0.6V范围内的控制步骤为带电离子的扩散控制;根据电极电位为0.0V左右时Nyquist图的圆弧半径判断,0.0V下的带电离子的迁移速率最小;由第二个氧化峰的Nyquist图可知随着电极电位的增加,羟基自由基产生的活性也增加,这点与循环伏安法分析结果一致。另外,通过交流阻抗谱图的拟合得到电极电位为-1.2V、-0.9V和-0.6V范围内的等效电路为:RS(Q1R1(Q2R2));0.0V电极电位左右对应的等效电路为:RS(QR1);第二个氧化反应电极范围内对应的等效电路为:RS(Q1R1)(Q2R2)。



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).