Enabling the anodic growth of highly ordered V2O5 nanoporous/nanotubular structures.
Enabling the anodic growth of highly ordered V2O5 nanoporous/nanotubular structures.
复制标题
DOI：
10.1002/anie.201104029
复制
发表时间：
2011-09
影响因子：
--
通讯作者：
Yang Yang-Yang;S. Albu;Doohun Kim;P. Schmuki
中科院分区：
文献类型：
--
作者：
Yang Yang-Yang;S. Albu;Doohun Kim;P. Schmuki
1995年，Masuda和Fukuda证明，在一组优化的电化学条件下，通过在草酸电解质中阳极氧化铝，可以在电化学上生长出高度有序、自组织的多孔氧化铝结构这引发了大量后续工作，这些工作直接使用这些结构（例如作为滤光片或光子材料）或间接作为模板，用于沉积各种材料，如纳米线、纳米棒或纳米管自组织多孔氧化物的生长被认为局限于氧化铝，直到1999年Zwilling等人引入了在含氟电解质中阳极氧化的钛电极上生长自组织TiO2纳米管在接下来的几年里，“稀”氟基电解质得到了改进，不仅允许不断增加对TiO2纳米管几何形状的控制，而且稀氟溶液也被发现非常通用，可以在其他金属（如Zr， Hf, Nb, Ta）和各种合金上生长高度有序的阳极纳米管或纳米孔层所有这些阳极氧化物生长过程的共同点是，水被用作氧化物形成的来源，氟化物被用来溶解多余的阳离子——这建立了一个形成-溶解的稳定状态。为了实现自组织氧化管或孔生长条件，需要优化电解质中H2O和FÀ的含量。一个困难是，稀氟溶液也会导致生成的氧化物结构的化学腐蚀，也就是说，在优化条件下，形成的氧化物对氟化物和H2O腐蚀的耐化学性可能变得至关重要。这对于Ta2O5或Nb2O5等氧化物来说没有问题（对于TiO2来说只是轻微的问题），但是极高的蚀刻敏感性阻碍了（尽管有许多尝试）从最重要的过渡金属氧化物之一V2O5中生长出确定有序的阳极层。在这里，我们展示了如何通过使用复杂的氟电解质（如[BF4] À或[TiF6] 2À）来克服这一问题，这首次允许成功地生长自组织的纳米孔和纳米管V2O5结构。由于V2O5在催化、锂电池、电致变色剂和传感器等方面的应用，它是研究最多的过渡金属氧化物之一，这一点具有特殊的意义在这些应用中，纳米几何结构在电子、磁性、催化和离子嵌入性能方面具有显著的优势迄今为止，V2O5纳米管的合成主要是通过水热处理来实现的，得到的是随机取向的组装体（纳米管粉末）利用电化学技术制备自组织V2O5纳米管或任何氧化钒的关键挑战是氧化钒在任何含水电解质中的不稳定性以及易于与各种阴离子形成高可溶性配合物。一些研究表明，在特定的非水电解质中生长致密的阳极氧化钒层或膜是可行的但在过去的几年里，许多尝试都以阳极生长V2O5纳米管或有序多孔层的失败告终几乎所有用于制造其他过渡金属氧化物纳米管或有序孔阵列的典型电解质都被探索过，但都失败了（此类尝试的概述汇编在支持信息表S1中）。在这里，我们证明了使用复杂的氟盐电解质，如[TiF6] 2À和[BF4] À，可以实现自组织阳极氧化。在第一种方法中，我们将纯钛溶解在HF中，然后将该溶液溶解在乙二醇中，形成[TiF6] 2À物质。
In 1995 Masuda and Fukuda demonstrated that highly ordered, self-organized porous alumina structures can electrochemically be grown by anodizing aluminium in an oxalic acid electrolyte under a set of optimized electrochemical conditions.[1] This initiated a large amount of follow-up work that used these structures either directly (eg as filters or photonic materials) or indirectly as a template for the deposition of a wide range of materials as nanowires, nanorods, or nanotubes.[2] Self-organized porous oxide growth was believed to be constrained to alumina, until in 1999 Zwilling et al. introduced the growth of self-organized TiO2 nanotubes from Ti electrodes when anodized in a fluoride-containing electrolyte.[3] In the following years, the “dilute” fluoridebased electrolytes were refined, not only to allow for an ever increasing control of the TiO2 nanotube geometry,[4] but dilute fluoride solutions were also found to be extremely versatile to grow highly ordered anodic nanotubes or nanoporous layers on other metals such as Zr, Hf, Nb, Ta, and a wide range of alloys.[5] Common to all these anodic oxide growth procedures is that water is used as a source for oxide formation and fluorides are used to solubilized excess cations—this establishes a formation–dissolution steady-state situation. To achieve self-organizing oxide tubes or pore-growth conditions, the H2O and FÀ contents in the electrolyte need to be optimized. A difficulty is that the dilute fluoride solutions also lead to chemical etching of the generated oxide structure, that is, for optimized conditions the chemical resistance of the formed oxide against fluoride and H2O etching may become crucial. This is no problem for oxides such as Ta2O5 or Nb2O5 (and only mildly for TiO2), but an extremely high etching susceptibility prevented (in spite of many attempts) the growth of defined ordered anodic layers from one of the most important transition-metal oxides, V2O5. Here, we show how to overcome this problem by using complex fluoride electrolytes such as [BF4] À or [TiF6] 2À, which allow for the first time, to successfully grow self-organized nanoporous and nanotubular V2O5 structures.This is of special significance as V2O5 is one of the most investigated transition-metal oxides because of its application in catalysis, lithium batteries, electrochromics, and sensors.[6] For many of these applications nanoscale geometries bear significant advantages in view of electronic, magnetic, catalytic, and ion intercalation properties.[7] Up to now the synthesis of V2O5 nanotubes was mainly achieved by hydrothermal treatments, which yield randomly oriented assemblies (a nanotube powder).[8] The key challenge for the preparation of self-organized V2O5 nanotubes or any vanadium oxide by electrochemical techniques is the instability of vanadium oxide in any watercontaining electrolyte and the ease of formation of highly soluble complexes with a wide range of anions. Some work has shown the feasibility to grow compact layers or films of anodic vanadium oxide in specific nonaqueous electrolytes.[9] But over the past few years numerous attempts failed to anodically grow V2O5 nanotubes or ordered porous layers.[10] Virtually any electrolyte that is typically used for fabricating other transition-metal oxide nanotubes or ordered pore arrays was explored but failed (an overview of such attempts is compiled in the Supporting Information, Table S1). Here, we demonstrate that using complex fluoride salt electrolytes such as [TiF6] 2À and [BF4] À enable self-organized anodization. In a first approach, we formed [TiF6] 2À species by dissolving pure titanium in HF and then dissolving this solution in ethylene glycol which was …