Performance-oriented pseudocapacitive energy storage of monovalent and divalent cation-driven Nb2CTx MXene electrodes

Restacking of two-dimensional materials, especially in MXene layers, hinders achieving potentially remarkable properties associated with these 2D nanosheets. In the MXene family, van der Waals and ionic restacking of Nb 2 CT x sheets mitigate their unique performance characteristics, rendering them an average performer compared to Ti-based MXenes. Herein, we propose the use of intercalating monovalent (Li 1+ , Na 1+ , and K 1+ ) and divalent (Mg 2+ ) ions to induce sheet separation, leading to high-performance Nb 2 CT x MXenes. Moreover, our findings highlight the understanding of the effect of various cation sizes on charge storage mechanisms and electrochemical characteristics in energy storage. The cation intercalation was performed via a self-electrostatic assembly method, which proves to be a simple, cost-effective, and scalable process. The effects of cation size on charge storage and electrochemical characteristics of MXenes for energy storage. The monovalent cation (K 1+ ) intercalated Nb 2 CT x MXene (870 F/g @ 5 mV/s) showed 6.85 times higher specific capacitance compared to pristine Nb 2 CT x MXene (127 F/g @ 5 mV/s). Moreover, the K +1 -Nb 2 CT x MXene posed low solution resistance (only ~0.23 Ω) and superior stability. In addition, the AC/K-Nb 2 CT x MXene device has demonstrated excellent power and energy density of 108 Wh/kg and 0.75 kW/kg at 1 A/g, respectively, making it a potential candidate for energy storage.