【作者】 刘东坡；

【导师】 冷文华；

【作者基本信息】 浙江大学 ， 化学， 2007， 硕士

【摘要】 近年来,除了在光电转换以及污染物降解处理等方面的应用外,半导体光催化剂的光电化学防腐蚀特性也逐渐引起研究者的兴趣。在半导体光催化剂对金属的光电化学防腐蚀保护过程中,需要的激发能量可取自于太阳能,且半导体光阳极本身并不牺牲,理论上具有很长的使用寿命和潜在的应用前景。目前金属的光电化学防腐蚀研究还处于探索阶段,阳极材料大多为宽禁带半导体如TiO₂,阴极材料主要局限于腐蚀电位比较正的不锈钢和铜等金属。主要研究半导体光催化剂对不锈钢和铜等金属的光致阴极保护的可行性,但对光致阴极保护的长效性尤其是光阳极的光电化学稳定性研究较少。论文首先应用电化学阻抗谱和稳态方法分别考察了不同方法制备的TiO₂光阳极反应动力学。结果表明锐钛矿和金红石混晶纳米多孔电极P25（德国,Degussa）和锐钛矿溶胶-凝胶纳米多孔电极SG的光电响应大于热氧化金红石块状电极TO和金红石纳米多孔电极RU。外加阳极偏压不仅降落在空间电荷层以抑制光生载流子复合,而且部分降落在Helmholtz层,即产生费米能级钉扎,并提高电荷转移速率常数,SG和P25电极费米能级钉扎程度比TO明显。其次研究了上述TiO₂光阳极的光电化学稳定性能、失活原因和再生途径。结果表明,SG、P25和TO三种电极在酸性和中性中比较稳定;在碱性中较差。电极光电化学稳定性顺序为:SG＜P25＜TO。SG电极光电化学不稳定性是可逆的,酸洗可以使其完全再生,为金属的长效光电化学防腐蚀提供了一条途径。最后考察了溶胶一凝胶TiO₂光阳极SG对碳钢、不锈钢等金属的光电化学防腐蚀效果。结果表明,阳极槽电解质溶液为含不同甲醇浓度的0.5 mol dm^-3Na₂SO₄+0.1 mol dm^-3NaOH,在5 mol dm^-3的NaCl中,500 W氙灯作为激发光源,SG光阳极可以实现对碳钢和不锈钢等金属的光致阴极保护作用,但防护效果随时间延长逐渐下降;在酸性、中性及纯水中都不同程度地加速了碳钢的腐蚀并对其原因进行了探讨。更多还原

【Abstract】 In recent decades, the photoelectochemical anticorrosion property of semiconductor has been drawn more attention besides its wide applications in light-electricity conversion and disposal of environmental pollutants. In the process of photoelectrochemical anticorrosion against metal, the excited energy can be derived from solar energy and photoanodes will not sacrifice, so that this method has long lifetime and potential application prospects. However, the recent researches are only on the threshold of this field. Most of the photoanode materials studied are the wide band gap semiconductors such as TiO₂ and the cathode materials are those metals with more positive corrosion potential such as stainless steel and copper. And the focus was concentrated on demonstrating the feasibility of photoelectrochemical anticorrosion against those metals. When it comes to the effect of TiO₂ photoelectrochemical stability, which plays a very important role in the protection process on the successive photocathode protection, we found there were few literatures studied about this.In the first part of this paper, we studied the kinetics of TiO₂ photoanodes attained by different methods using electrochemical impedance spectroscopy under different applied anodic potential and steady state measurements. The later experiments present the photoresponse of electrode P25 （Germany, Degussa） and nanoporous electrode SG derived by sol-gel, was more effective than that of rutile nanoporous electrode RU and electrode TO derived by thermal oxidation. And the EIS results show that all the TiO₂ photoanodes are not ideal semiconductor electrodes; some of the applied potential dropped over the Helmholtz layer, i.e.Fermi level pinning, changing the charge transfer constant, which would affect the photovoltage, instead of dropping over the space charge layer thoroughly to suppress the recombination of photogenerated carriers. The effect of such a pinning of the SG and P25 electrodes was more obvious than that of TO.In the second part, we studied the photoelectrochemical stability of TiO₂ photoanode. Three kinds of TiO₂ electrodes with different crystalline were prepared and the effects of different experimental conditions on the photoelectrochemical stability of TiO₂ such as pH value, concentration of hole scavenger etc were investigated. It turned out that all the photoanodes studied were photoelectrochemically stable in acid and neutral conditions but less stable in alkaline condition, especially for SG photoanodes. The photoelectrochemical stability followed the order: SG < P25 < TO. Such instability is, however, revisable and could be recovered by immersing in acid medium. According to the experimental results, we proposed the most probable mechanism that could explain our results very satisfactorily. This provides a method for photoelectrochemical anticorrosion against metal for long term.In the last part, the photoelectrochemical anticorrosion of SG photoanodes against carbon steel and stainless steel was studied. It was found that the SG photoanodes could protect carbon steel from corrosion under the conditions that corrosion electrolyte was 5 mol dm^-3 NaCl and the light source was 500 W Xe lamp, the electrolyte in anodic compartment was 0.5 mol dm^-3 Na₂SO₄ + 0.1 mol dm^-3 NaOH with or without methanol, but the protection effect was losing gradually. However, the corrosion rate was accelerated in acid, neutral conditions and in pure water of different extent. The possible reason was also discussed briefly in this part.更多还原