Double cross-linking system for constructing tortuosity-lowered and strength-enhanced porous MXene films with superior capacitive performance and electromagnetic shielding efficiency

Porous MXene films are ideal materials for flexible electronics because of their various porous structures and rich surface chemistry. However, the typical problem, especially as flexible supercapacitors, is that MXene lamellae are still prone to stacking. Many channels are disconnected from each other, facing high ion transport resistance. Herein, an optimal 3D structure is built by ion-molecular double cross-linking system and subsequent freeze-casting with lowered-tortuosity and enhanced-strength for porous MXene films. Ionic cross-linking is used to adjust the orientation of the MXene lamellae by coulombic attraction, while optimized terminal and ion intercalation widens the layer spacing. Molecular cross-linking is used to adjust the backbone of the porous structure through hydrogen bonding interactions. As a result, due to the porous structure of connectivity, the porous MXene-OH/BC (MOB) delivers a capacitance of 527 F g-1, mechanical property of 41.5 MPa (140 % and 367 % of the MXene film, respectively), and the shielding efficiency of 67.2 dB (X-bond). In addition, the assembled NAC//MOB device achieves high energy density of 56.28 Wh kg-1 and 85.6 % capacitance retention after 50,000 cycles. This work shows a well-designed porous film with lightweight, flexible and strong mechanical properties, expanding the competitiveness of MXene materials for real-world applications.