On March 21, 2022, the founding editor of nano research energy and Professor Zhi Chunyi of City University of Hong Kong published the latest research results entitled "building durable k-ion capacitors based on mxene family".

Supercapacitors are widely used in various scenarios, such as wearable electronic energy supply devices and large-scale energy storage. Compared with widely used lithium-ion capacitors, potassium has abundant storage capacity on earth, which is expected to build low-cost capacitors. However, the low energy density of aqueous potassium ion capacitor is the bottleneck of its further practical application. Compared with the common electric double-layer capacitors based on adsorption desorption, the pseudo capacitor dominated capacitors show a significant increase in energy density. However, the structural stability of the electrode materials based on the pseudo capacitance dominated embedding and stripping type or surface oxidation reduction type will decline in the long cycle process, resulting in unsatisfactory cycle stability. Therefore, the development of high specific energy electrode materials dominated by PSEUDOCAPACITORS for storing potassium ions and taking into account their cycle stability is the key problem to realize high energy density and long cycle potassium ion capacitors.

To solve the above problems, Professor Zhi Chunyi's team used different mxene (nb2c, ti2c and Ti3C2) materials as potassium storage electrode materials, and compared the potassium storage properties of the three horizontally. Based on the good conductivity of mxene material itself, the abundant oxidized surface groups on the surface as the interaction sites of pseudocapacitance, and the great layer spacing used to embed the potassium ion of stripping storage, mxene has achieved excellent potassium storage performance. Among them, the k-ion capacitor of nb2c mxene has the most outstanding performance, with the highest power density of 2336 w / kg and energy density of 24.6 WH / kg, showing excellent potassium storage energy density. When the potassium ion capacitor was constructed by pairing with the organic negative electrode perylene tetraformyl diimide (PTCDI), the capacity of the capacitor of nb2c ║ PTCDI remained 94.6% of the initial capacity after 30000 cycles at a current density of 5 A / g, showing super stable cycle stability (Fig. 1). As a super stable potassium storage electrode material, mxene provides a good reference for the development of other aqueous potassium ion electrode materials.

Figure 1: ultrafast and ultra stable aqueous potassium ion capacitor based on mxene family electrode materials (a) Schematic diagram of potassium storage process of three different mxene electrode materials; (b) Schematic diagram of water system potassium ion capacitor; (c) Ultrafast storage and super stable cycle stability of nb2c potassium ion capacitor under high current.

As a sister Journal of nano research, Nano Research Energy  (ISSN: 2791-0091; e-issn: 2790-8119; founded in March 2022, it is sponsored by Tsinghua University and co edited by Professor Qu liangti of Tsinghua University and Professor Zhi Chunyi of City University of Hong Kong. Nano research energy is an international interdisciplinary, all English open access periodical, focusing on the cutting-edge research and application of nano materials and nano science and technology in new energy related fields, benchmarking with international top energy journals and committed to publication High level original research and review papers.

(original title: Construction of ultra long circulating water potassium ion capacitor based on mxene electrode)