Wang Zixing, Xu Zhong, Huang Haichao, Chu Xiang, Xie Yanting, Xiong Da, Yan Cheng, Zhao Haibo, Zhang Haitao, Yang Weiqing
Key Laboratory of Advanced Technologies of Materials (Ministry of Education), School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, P.R. China.
State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P.R. China.
ACS Nano. 2020 Apr 28;14(4):4916-4924. doi: 10.1021/acsnano.0c01056. Epub 2020 Mar 23.
Rich chemistry and surface functionalization provide MXenes enhanced electrochemical activity yet severely exacerbate their self-discharge behavior in supercapacitors. However, this self-discharge behavior and its related mechanism are still remaining issues. Herein, we propose a chemically interface-tailored regulation strategy to successfully unravel and efficiently alleviate the self-discharge behavior of TiCT MXene-based supercapacitors. As a result, TiCT MXenes with fewer F elements (∼0.65 atom %) show a positive self-discharge rate decline of ∼20% in comparison with MXenes with higher F elements (∼8.09 atom %). Such decline of the F elements can highly increase tight-bonding ions corresponding to an individual self-discharge process, naturally resulting in a dramatic 50% increase of the transition potential (). Therefore, the mixed self-discharge rate from both tight-bonding (contain fewer F elements) and loose-bonding ions (contain more F elements) is accordingly lowered. Through chemically interface-tailored engineering, the significantly changed average oxidation state and local coordination information on MXene affected the interaction of ion counterparts, which was evidently revealed by X-ray absorption fine structures. Theoretically, this greatly improved self-discharge performance was proven to be from higher adsorption energy between the interface of the electrode and the electrolyte by density functional theory. Therefore, this chemically interface-tailored regulation strategy can guide the design of high-performance MXene-based supercapacitors with low self-discharge behavior and will promote its wider commercial applications.
丰富的化学性质和表面功能化赋予MXenes增强的电化学活性，但在超级电容器中却严重加剧了它们的自放电行为。然而，这种自放电行为及其相关机制仍是有待解决的问题。在此，我们提出一种化学界面定制调控策略，成功揭示并有效缓解了基于TiCT MXene的超级电容器的自放电行为。结果，与具有较高F元素含量（约8.09原子%）的MXenes相比，F元素含量较少（约0.65原子%）的TiCT MXenes的自放电速率正向下降约20%。F元素含量的这种下降可大幅增加对应单个自放电过程的紧密结合离子，自然导致过渡电位大幅增加50%。因此，紧密结合（含较少F元素）和松散结合离子（含较多F元素）的混合自放电速率相应降低。通过化学界面定制工程，MXene上显著变化的平均氧化态和局部配位信息影响了离子对的相互作用，这在X射线吸收精细结构中得到明显揭示。从理论上讲，这种大幅改善的自放电性能经密度泛函理论证明源于电极与电解质界面之间更高的吸附能。因此，这种化学界面定制调控策略可指导设计具有低自放电行为的高性能基于MXene的超级电容器，并将推动其更广泛的商业应用。
