Size-Scaling of Proton Conductivity in Amorphous Aluminosilicate Acid Thin Films
Size-Scaling of Proton Conductivity in Amorphous Aluminosilicate Acid Thin Films
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DOI：
10.1021/ja904627h
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发表时间：
2009-10-14
影响因子：
15
通讯作者：
Kunitake, Toyoki
中科院分区：
文献类型：
--
作者：
Aoki, Yoshitaka;Habazaki, Hiroki;Kunitake, Toyoki
无定形铝硅酸盐纳米膜a-Al0.1Si0.9Ox，由于在玻璃基体内部存在类似沸石的、具有介观尺寸的酸位网络，在厚度方向上表现出独特的质子电导率的尺寸增强。采用混合前驱体溶胶进行多次旋涂，在电极衬底上均匀地形成了厚度为22 ~ 1400 nm的纳米级致密薄膜。XANES测试表明，a- al0.1 si0.9 ox薄膜的基本骨架类似于沸石结构，由SiO4和AlO4四面体单元的角连接组成。通过两种质子载体的存在：Bronsted酸性质子和Lewis酸性质子，揭示了质子电导率的复杂温度和湿度依赖性。通过热解吸光谱检测，在500℃左右的温度下，Bronsted酸性质子可以在非晶态薄膜中持续存在，因此在300℃以上的温度下，薄膜表现出与湿度无关的质子电导率。此外，通过将薄膜厚度减小到小于120 nm （sigma与d-(tau)成正比），薄膜的电导率呈低功率增加，当厚度小于40 nm时，薄膜达到饱和。观察到的结垢指数tau为2.2，与三维渗流系统中聚类大小结垢的理论指数（2.3）值一致。这种传导行为可以用基于互连的Bronsted酸中心在几十到几百纳米范围内的高导电途径的有限尺寸缩放来解释。
Amorphous aluminosilicate nanofilms, a-Al0.1Si0.9Ox, exhibit unique size-enhancement of the proton conductivity along the thickness direction because of the presence of the zeolite-like, acid site network with the mesoscopically sized dimension inside glass matrix. The dense films with the thickness of 22-1400 nm were uniformly formed over the electrode substrate in nanometer thickness precision by multiple spin-coating with a mixed precursor Sol. XANES measurements indicated that the basic framework of a-Al0.1Si0.9Ox films was similar to the zeolitic one, consisting of the corner-linkage Of SiO4 and AlO4 tetrahedral units. These films revealed the complex temperature- and humidity-dependency of proton conductivity by the existence of two kinds of protonic carriers: Bronsted acidic protons and Lewis acidic protons. The Bronsted acidic protons could be persistent in amorphous films at around 500 degrees C, as checked by thermal desorption spectroscopy, so that the film exhibited the humidity-independent proton conductivity at temperatures above 300 degrees C. Furthermore, the conductivity across the film a increased in a power low by reduction of the film thickness of to less than 120 nm as sigma proportional to d-(tau), and it was saturated when the thickness become less than 40 nm. The observed scaling index tau was 2.2 in agreement with the value of the theoretical index (2.3) of cluster size scaling in a three-dimensional percolation system. This conduction behavior is explicable by finite size-scaling of the highly conductive pathway based on the interconnected Bronsted acid centers in the range of a few tens to hundreds of nanometers.