阳极氧化制备新颖的TiO_2多孔纳米结构膜及其形成机理与应用

The fabrication,formation mechanisms and applications of novel nanoporous TiO_2 membranes prepared by anodization

采用两步阳极氧化法在钛箔片上制备了TiO_2多孔薄膜,随着阳极氧化的进行,Ti片表面依次出现上下双层纳米多孔结构、内外双层(芯壳)纳米管阵列结构和单层纳米管阵列结构等典型形貌,结合不同时间段的阳极氧化膜的表面形貌、晶体结构、X射线光电子能谱、电流密度随时间变化曲线等,分析了随着氧化进行钛片表面多孔TiO_2纳米膜典型形貌可能的形成机理.上下双层结构纳米多孔膜可能是因为纳米孔孔径强烈依赖于电流密度,而起始阶段的电流密度大小指数下降导致出现上层大孔下层小孔的双层结构;内外双层结构纳米多孔膜的形态可能来自于氧化钛纳米多孔膜从内至外由成分和可溶性不同的氧化钛构成导致;随着氧化进行,内层可溶性大的氧化钛结构逐渐溶解,形成的常见的TiO_2纳米管阵列结构.将阳极氧化得到的稳定的TiO_2纳米管薄膜作为光阳极组装成染料敏化太阳能电池,研究了其光电性能.基于未经修饰处理的TiO_2纳米管阵列光阳极,其组装电池的能量转换效率(η)可达5.88%,将TiO_2纳米管阵列光阳极进一步采用常用的TiCl_4溶胶处理后,其效率提高到8.47%,在能源转化方面展现了较好的应用前景.

In this paper, the TiO_2 nanoporous membranes were prepared by a two-step anodization method on Ti foils. The novel overlapped porous nanostructure, core-shell nanotube arrays and normal nanotubes arrays were successively observed during the anodization process. The formation mechanisms of such novel porous nanostructures were proposed based on the results and analysis of the surface morphology, crystallographic structure, X-ray photoelectron spectroscopy analysis and time-dependent current density curves. The overlapped porous nanostructure may originate from the exponential decay of current density during the initial stage.The nanopore diameter significantly depends on the current density; the large current density causes large nanopores on the top layer and the successive deceased current density results in the small nanopores in the under layer. The core-shell nanotubes arrays structure was suggested to relate with the composition and solubility of the anodized nanotubes. From the inner to the outer, each tube consists of several kinds of titanium oxide layers with different composition and different solubility. With further anodization,the inner layer titanium oxide, with high solubility in the electrolyte, could be gradually dissolved by the solution, which results in the formation of the normal nanotubes arrays. The finally obtained stable TiO_2 nanotube arrays were used as anodes to assemble dye-sensitized solar cells（DSSCs）, and the photovoltaic performance of the cells were studied. The cell based on TiO_2 nanotube arrays without any surface modification gives a power conversion efficiency（η） up to 5.88%. After treating the TiO_2 nanotube arrays by TiCl_4 sol solution, the efficiency of the assembled cell increases to 8.47%, exhibiting a well prospect in energy conversion.