High power K+ ion capacitors have great potential in various large-scale applications because of the cost advantages and the low redox potential of K/K+. However, the large ionic radius of potassium brings huge challenges for the development of suitable electrode materials. Here we demonstrate a general strategy for preparing porous MXene electrodes that can significantly enhance K+ storage performance. Using V2C MXene as a model system, we show that the K+ ion storage capacity can be greatly boosted by a simple sequential acid/alkali treatment. The resulting product, K–V2C, not only delivers a capacity of 195 mAh g−1 (in contrast to 98 mAh g−1 of pristine V2C) at 50 mA g−1, but also good rate performance. The charge storage mechanism was carefully studied and is shown to involve a solvent co-intercalation process. In addition, full cells were fabricated by coupling the K–V2C anode and Prussian blue analogous (KxMnFe(CN)6) cathode, which can work at a high average operating voltage of ~3.3 V within a wide range (0.01 V–4.6 V). Moreover, the devices can achieve a high energy density of 145 Wh kg−1 at a power density of 112.6 W kg−1, suggesting that K–V2C, and other porous MXenes prepared by our approach, are promising electrodes in mobile ion capacitors.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The research reported in this publication was supported by King Abdullah University of Science and Technology (KAUST). Authors thank the Advanced Nanofabrication, Imaging and Characterization Laboratory at KAUST for their excellent support.