Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
ACS Nano. 2010 Feb 23;4(2):967-77. doi: 10.1021/nn9007324.
In this work, we report the synthesis and characterization of highly ordered mesoporous CeO(2) thin films with crystalline walls. While this article focuses on electrochemical studies of CeO(2) with periodic nanoscale porosity, we also examine the mechanical properties of these films and show how pore flexing can be used to facilitate intercalation of lithium ions. Mesoporous samples were prepared by dip-coating using the large diblock copolymer KLE as the organic template. We establish that the films have a mesoporous network with a biaxially distorted cubic pore structure and are highly crystalline at the atomic scale when heated to temperatures above 500 degrees C. Following a previously reported approach, we were able to use the voltammetric sweep rate dependence to determine quantitatively the capacitive contribution to electrochemical charge storage. The net result is that mesoporous CeO(2) films exhibit reasonable levels of pseudocapacitive charge storage and much higher capacities than samples prepared without any polymer template. Part of this increased capacity stems from the fact that these films are able to expand normal to the substrate upon intercalation of lithium ions by flexing of the nanoscale pores. This flexing relieves stress from volume expansion that normally inhibits charge storage. Overall, the results described in this work provide fundamental insight into how nanoscale structure and mechanical flexibility can be used to increase charge storage capacity in metal oxides.
在这项工作中，我们报告了具有结晶壁的高度有序介孔 CeO(2) 薄膜的合成和表征。虽然本文侧重于具有周期性纳米级孔隙率的 CeO(2) 的电化学研究，但我们还研究了这些薄膜的机械性能，并展示了如何通过孔弯曲来促进锂离子的嵌入。介孔样品是通过使用大的两亲嵌段共聚物 KLE 作为有机模板的浸涂制备的。我们确定这些薄膜具有具有双轴扭曲立方孔结构的介孔网络，并且当加热到 500 度以上的温度时，在原子尺度上高度结晶。根据先前报道的方法，我们能够使用伏安扫描速率依赖性来定量确定电化学电荷存储的电容贡献。最终结果是，介孔 CeO(2) 薄膜表现出合理的赝电容电荷存储水平，并且比没有任何聚合物模板制备的样品的容量高得多。这种增加的部分容量源于这样一个事实，即这些薄膜能够在锂离子嵌入时通过纳米级孔的弯曲而垂直于衬底扩展。这种弯曲缓解了通常抑制电荷存储的体积膨胀引起的应力。总体而言，这项工作中描述的结果提供了基本的见解，说明如何利用纳米级结构和机械灵活性来提高金属氧化物的电荷存储容量。
