Hierarchical Porous MXene QDs/Graphene Composite Fibers for High-Performance Supercapacitors

Fiber-typed supercapacitors are promising energy storage devices for wearable electronics, and the microstructure of graphene fiber electrodes for flexible supercapacitors plays a significant role in the ion diffusion efficiency and energy density improvement. In this paper, we report a coaxial microfluidic spinning technology, ammonium bicarbonate solution as the core flow, and graphene oxides and MXene quantum dots (MQDs) composite spinning dispersion as the sheath flow to fabricate the hierarchical porous MQDs/graphene composite fibers (MQDs@PGF). 0D MQDs as electrochemically active materials were intercalated into graphene nanosheets; the ammonium bicarbonate solution acts as a foaming agent to realize a hierarchical porous structure of micro-meso-macroporous and a large specific surface area (68.8 m2 g- 1), which greatly shorten the ion diffusion channels and provide more electrochemically active sites. The assembled fiber-typed supercapacitors (MQDs@PGF FSCs) exhibit a high specific areal capacitance of 1288 mF cm-2 and maintain a high capacitance retention of 95% after 9000 cycles. The MQDs@PGF FSCs achieve an excellent energy density of 147.5 mu Wh cm-2 under a wide operating voltage window of 0-2.5 V and successfully power small electronic devices. This method provides a strategy for the controllable design of high-performance fiber electrode materials and promotes energy storage applications in wearable portable devices.