Local atomic structure and conduction mechanism of nanocrystalline hydrous RuO2 from X-ray scattering
Local atomic structure and conduction mechanism of nanocrystalline hydrous RuO2 from X-ray scattering
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DOI：
10.1021/jp026228l
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发表时间：
2002-12-12
影响因子：
3.3
通讯作者：
Rolison, DR
中科院分区：
文献类型：
--
作者：
Dmowski, W;Egami, T;Rolison, DR
水合氧化钌（RuO2）xH(2)O或RuOxHy)是一种质子-电子混合导体，可用于燃料电池和超级电容器。其电荷存储（赝电容）和电催化性能随含水量的变化而变化，在RuO2.0.5 mol % H2O附近达到最大。我们研究了RuO2的原子结构。利用x射线衍射和原子对密度函数（PDF）计算出xH(2)O在x = 0.84至0.02范围内与含水量的函数关系。尽管含有0.84 ~ 0.35摩尔水的样品的衍射图显示出“非晶”结构，但PDF分析清楚地表明，在0.7 nm以内，所有这些RuO2的短程原子结构都是稳定的。xH(2)O样品类似于无水金红石RuO2结构。我们得出RuO2。xH(2)O是一种由无水金红石状RuO2纳米晶体组成的复合材料，这些晶体分散在与Ru-O相关的结构水的边界上。金红石状纳米晶体支持金属传导，晶界结构水促进质子传导。这张结构图解释了RuO2的电荷存储和电催化性能。xH(2)O在金属和质子传导途径的竞争渗透网络方面，其体积变化作为ruo2的含水量的函数。控制和优化电子和质子的传导体积和途径将导致性能的提高，并指导新材料的设计。
Hydrous ruthenium oxide (RuO2.xH(2)O or RuOxHy) is a mixed proton-electron conductor which could be used in fuel cells and ultracapacitors. Its charge-storage (pseudocapacitance) and electrocatalytic properties vary with water content and are maximized near, the composition RuO2.0.5 mol % H2O. We studied the atomic structure of RuO2.xH(2)O as a function of water content from x = 0.84 to 0.02 using X-ray diffraction and atomic pair density function (PDF). Even though the diffraction patterns of samples containing 0.84 to 0.35 mole of water are suggestive of "amorphous" structures, the PDF analysis clearly shows that up to 0.7 nm, the short-range atomic structure of all of these RuO2.xH(2)O samples resembles that of the anhydrous rutile RuO2 structure. We conclude that RuO2.xH(2)O is a composite of anhydrous rutile-like RuO2 nanocrystals dispersed by boundaries of structural water associated with Ru-O. Metallic conduction is supported by the rutile-like nanocrystals, while proton conduction is facilitated by the structural water along the grain boundaries. This structural picture explains the charge-storage and electrocatalytic properties of RuO2.xH(2)O in terms of competing percolation networks of metallic and protonic conduction pathways, that vary in volume as a function of the water content of the RuO2.xH(2)O. The control and optimization of electron and proton conducting volumes and pathways will lead to improved performance and guide the design of new materials.