Ningbo Institute of Materials Technology and Engineering , Chinese Academy of Sciences , Ningbo , Zhejiang 315201 , China.
Department of Chemistry , University of Nebraska-Lincoln , Lincoln , Nebraska 68588 , United States.
ACS Appl Mater Interfaces. 2018 Dec 19;10(50):43595-43602. doi: 10.1021/acsami.8b14446. Epub 2018 Dec 5.
A recent experiment [ Jin , E. ; Science 2017 , 357 , 673 - 676 ] shows that the conductivity of a two-dimensional (2D) sp-carbon-hybridized π-conjugated covalent organic framework (sp-c-COF) can be enhanced by as much as 12 orders of magnitude after iodine oxidation processing. To understand the physical mechanism underlying such a huge increase in the conductivity, we perform multiscale computations and find that the high conductivity of the iodine-oxidized 2D COF can be attributed to both hole transfer and ion transfer within the 2D COF. The computed dominant charge distribution corresponding to the valence band maximum (VBM) suggests that the delocalized π electrons occur mostly at the active reaction sites. The computed low ionization energy at the active reaction sites further supports that the 2D COF tends to lose electrons during iodine oxidation and to yield cationic COF and anionic triiodide I. Complementary classical molecular dynamics simulation shows a relatively high anion conductivity of 13.63 × 10 S m, consistent with the high conductivity measured from the experiment (7.1 × 10 S m). Meanwhile, we find that the cations in 2D COF can also induce a shift of the Fermi level to cross the valence band, thereby enhancing the hole mobility to 86.75 cm V s. For proposing a potential application of the highly conductive iodine-oxidized 2D sp-c-COF, we design a prototypical model of the 2D spirally wound lithium-ion battery and find that it exhibits enhanced stability than a typical electrolyte material.
最近的一项实验[Jin, E.; Science 2017, 357, 673-676]表明，经过碘氧化处理后，二维（2D）sp 杂化π共轭共价有机骨架（sp-c-COF）的电导率可增强多达 12 个数量级。为了理解这种电导率大幅提高的物理机制，我们进行了多尺度计算，发现碘氧化二维 COF 的高电导率可归因于二维 COF 内的空穴转移和离子转移。计算得出的对应价带最大值（VBM）的主导电荷分布表明，离域π电子主要出现在活性反应部位。活性反应部位的低电离能进一步表明，在碘氧化过程中，二维 COF 倾向于失去电子，并产生阳离子 COF 和阴离子三碘化物 I。补充的经典分子动力学模拟显示，阴离子电导率相对较高，为 13.63×10 S m，与实验测量的高电导率（7.1×10 S m）一致。同时，我们发现二维 COF 中的阳离子也可以引起费米能级向价带移动，从而将空穴迁移率提高到 86.75 cm V s。为了提出高导电性碘氧化二维 sp-c-COF 的潜在应用，我们设计了二维螺旋缠绕锂离子电池的原型模型，并发现其稳定性优于典型的电解质材料。
