Synthesis and Electrochemical Properties of Two-Dimensional Hafnium Carbide

Jie Zhou, Xianhu Zha, Xiaobing Zhou, Fanyan Chen, Guoliang Gao, Shuwei Wang, Cai Shen, Tao Chen, Chunyi Zhi, Per Eklund, Shiyu Du, Jianming Xue, Weiqun Shi, Zhifang Chai, Qing Huang

We demonstrate fabrication of a two-dimensional Hf-containing MXene, Hf3C2Tz, by selective etching of a layered parent Hf3[Al(Si)]4C6 compound. A substitutional solution of Si on Al sites effectively weakened the interfacial adhesion between Hf-C and Al(Si)-C sub-layer within the unit cell of the parent compound, facilitating the subsequent selective etching. The underlying mechanism of the Si-alloying-facilitated etching process is thoroughly studied by first-principles density functional calculations. The result showed that more valance electrons of Si than Al weaken the adhesive energy of the etching interface. The MXenes were determined to be flexible and conductive. Moreover, this 2D Hf-containing MXene material showed reversible volumetric capacities of 1567 mAh cm-3 and 504 mAh cm-3 for lithium and sodium ions batteries, respectively, at a current density of 200 mAg-1 after 200 cycles. Thus, Hf3C2Tz MXenes with 2D structure is a candidate anode material for metal-ion intercalation, especially for applications where size matters.