Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea.
ACS Nano. 2013 Mar 26;7(3):2453-60. doi: 10.1021/nn305750s. Epub 2013 Feb 18.
Development of nanostructured materials with enhanced redox reaction capabilities is important for achieving high energy and power densities in energy storage systems. Here, we demonstrate that the nanohybridization of ionic liquids (ILs, 1-butyl-3-methylimidazolium tetrafluoroborate) and cobalt hydroxide (Co(OH)2) through ionothermal synthesis leads to a rapid and reversible redox reaction. The as-synthesized IL-Co(OH)2 has a favorable, tailored morphology with a large surface area of 400.4 m(2)/g and a mesopore size of 4.8 nm. In particular, the IL-Co(OH)2-based electrode exhibits improvement in electrochemical characteristics compared with bare Co(OH)2, showing a high specific capacitance of 859 F/g at 1 A/g, high-rate capability (∼95% retention at 30 A/g), and excellent cycling performance (∼96% retention over 1000 cycles). AC impedance analysis demonstrates that the introduction of ILs on Co(OH)2 facilitates ion transport and charge transfer: IL-Co(OH)2 shows a higher ion diffusion coefficient (1.06 × 10(-11) cm(2)/s) and lower charge transfer resistance (1.53 Ω) than those of bare Co(OH)2 (2.55 × 10(-12) cm(2)/s and 2.59 Ω). Our density functional theory (DFT) calculations reveal that the IL molecules, consisting of anion and cation groups, enable easier hydrogen desorption/adsorption process, that is, a more favorable redox reaction on the Co(OH)2 surface.
开发具有增强氧化还原反应能力的纳米结构材料对于在储能系统中实现高能量和功率密度非常重要。在这里，我们证明通过离子热合成将离子液体（IL，1-丁基-3-甲基咪唑四氟硼酸盐）和氢氧化钴（Co(OH)2）纳米杂交导致快速和可逆的氧化还原反应。所合成的 IL-Co(OH)2具有有利的、定制的形态，具有 400.4 m(2)/g 的大表面积和 4.8 nm 的中孔尺寸。特别是，与裸 Co(OH)2 相比，基于 IL-Co(OH)2 的电极表现出改善的电化学特性，在 1 A/g 时具有 859 F/g 的高比电容、高倍率性能（在 30 A/g 时保持约 95%）和出色的循环性能（在 1000 次循环中保持约 96%）。交流阻抗分析表明，ILs 的引入促进了 Co(OH)2 上的离子传输和电荷转移：IL-Co(OH)2 表现出比裸 Co(OH)2 更高的离子扩散系数（1.06 × 10(-11) cm(2)/s）和更低的电荷转移电阻（1.53 Ω）（2.55 × 10(-12) cm(2)/s 和 2.59 Ω）。我们的密度泛函理论（DFT）计算表明，由阴离子和阳离子基团组成的 IL 分子使氢的脱附和吸附过程更容易，即在 Co(OH)2 表面发生更有利的氧化还原反应。
