MXene异质结Ti-O-H-O电子快速通道促进高效率储钾

Efficient Potassium Storage through Ti-O-H-O Electron Fast Track of MXene Heterojunction

二维层状结构MXenes因其优异的电学性能、可调控的表面官能团而被广泛应用于钾离子超级电容器领域,但其有限的双电容存储容量严重限制了MXenes在电极材料方面的应用。本工作采用“路易斯酸熔盐预刻蚀+液相刻蚀+原位水热复合”策略,制备了以Ti_(3)C_(2)为基体、表面包覆MnO_(2)的Ti_(3)C_(2)基异质结,以提高电极材料对钾离子的储存。采用基于密度泛函理论的第一性原理计算方法,研究了Ti_(3)C_(2)基异质结界面之间的连接方式、电学性质以及钾离子吸附规律的变化。结果表明构建的Ti_(3)C_(2)基异质结对钾离子的最大吸附量是Ti_(3)C_(2)的3倍左右,且Ti–O–H–O连接通道使MnO_(2)内部的自由电子数量增多,使Ti_(3)C_(2)基异质结表现出优异的电学性能。三电极体系下的电化学测试结果表明Ti_(3)C_(2)基异质结在1 A·g^(-1)的电流密度下能够提供431 F·g^(-1)的比电容,远远高于Ti_(3)C_(2)(128 F·g^(-1))。并通过动力学分析阐述了Ti_(3)C_(2)基异质结的赝电容储能机理,在100 mV·s^(-1)的扫描速率下,其赝电容贡献比例高达89%,此外Ti_(3)C_(2)基异质结表现出较小的电化学阻抗,从而提高了钾离子传输速率、电子转移速率。本研究通过构筑Ti_(3)C_(2)基异质结,提高了基体Ti_(3)C_(2)的电化学性能,并阐述了相应的储能机理,这为设计其他MXenes基电极材料提供了理论基础。

MXenes with two-dimensional layered structure are widely used in the field of potassium ion supercapacitors because of their excellent electrical properties and adjustable surface functional groups,but their limited dual-capacitor storage capacity severely retards the application of MXenes materials in electrode materials.In this work,the strategy of“Lewis acid molten salt pre-etching+liquid phase etching+in situ hydrothermal recombination”was used to prepare the Ti_(3)C_(2)-based heterojunction with Ti_(3)C_(2)as matrix and MnO_(2) coated surface to improve the storage of potassium ions in electrode materials.The connection mode,electrical properties and the change of potassium adsorption law at Ti_(3)C_(2)-based heterojunction interfaces were studied by using the first principles calculation method based on density functional theory.The results show that the maximum adsorption capacity of potassium ions in the constructed Ti_(3)C_(2)-based heterojunction is about 3 times that of Ti_(3)C_(2).The presence of Ti–O–H–O connecting channel increases the number of free electrons in MnO_(2),causing Ti_(3)C_(2)-based heterojunction exhibiting excellent electrical properties.The electrochemical test results of the three-electrode system show that,at a current density of 1 A·g^(-1),Ti_(3)C_(2)-based heterojunction can provide 431 F·g^(-1)specific capacitance which is much higher than 128 F·g^(-1)of bare Ti_(3)C_(2).At a voltage sweep rate of 100 mV·s^(-1),the contribution of pseudocapacitance is up to 89%.In addition,the Ti_(3)C_(2)-based heterojunction exhibits lower electrochemical impedance,which improves the potassium ion transport rate and electron transfer rate.Therefore,this study demonstrates that the electrochemical performance of Ti_(3)C_(2)matrix can be improved by constructing Ti_(3)C_(2)-based heterojunction,and the corresponding energy storage mechanism can provide a theoretical basis for the design of other MXenes-based electrode materials.