高电容性能MXene电极对插层修饰离子的选择性

Selectivity for intercalated ions in MXene toward a high-performance capacitive electrode

离子插层是提高Ti_(3)C_(2)TxMXene电化学性能的有效方法之一.然而,不同的插层离子对MXene的结构和电化学性能的影响是否相同这一问题尚不清楚.本文系统研究了Li+、Na+、K+、Cs+、Zn2+、Mg2+、SO_(4)2-和OH-等一系列离子插层后的MXene的结构特征和电化学性能.研究结果表明,插层离子的半径、电荷数和化学特性对插层效果都会产生影响.在所研究的插层剂中,由离子半径最大的一价阳离子Cs+和具有强碱性的阴离子OH-组成的插层剂CsOH对MXene具有较好的插层效果.插层后的MXene层间距增大,层间容纳了大量游离水,Ti的价态升高,片层表面有利于氧化还原反应的含O官能团增多,这都大大促进了电解液离子H+的扩散与存储.由此制备的电极的质量比电容大幅度提高,为原始MXene电极的7倍多,而且经过20,000次充放电循环后电容保持率未发生下降.本文为具有高电容性能的MXene和MXene基复合电极的合理设计和制备提供了指导.

The intercalation of foreign ions has been demonstrated to be one of the effective methods to improve the electrochemical performance of Ti_(3)C_(2)TxMXene.However,whether different intercalated ions have diverse impacts on the MXene structure and electrochemical properties is not well understood.Herein,we comprehensively investigated the structural features and electrochemical performances of a series of ions,including Li+,Na+,K+,Cs+,Zn2+,Mg2+,SO_(4)2-,and OH-intercalated MXenes.Different ions are observed to exhibit variations in the intercalation effect because of the differences in their sizes,charge numbers,and chemical features.Among the investigated intercalation agents,CsOH composed of monovalent Gs+with a large size and strong base anion OH-exhibits a superior intercalation effect,where a large interlayer space accommodating a large amount of free water,a high oxidation state of Ti and a preferred surface with more O-containing functional groups for redox reaction is created,intensifying the pseudocapacitive H+intercalation.Therefore,CsOH-treated MXene exhibits a significant enhancement in gravimetric capacitance(i.e.,approximately725% of the original) and more than 100% capacitance retention over 20,000 cycles.This paper provides a guideline for the rational design and construction of high-capacitance MXene and MXene-based hybrid electrodes in aqueous electrolytes.