Interfacial engineering of NiO-carbon black decorated MXene for high-performance asymmetric supercapacitors

MXene is a conductive and mechanically robust two-dimensional material that suffers from fewer redox-active charge storage sites and self-aggregation. MXene was synthesized from the MAX phase by LiF/HCl etching. Carbon black (CB) nanoparticles were then intercalated between the MXene sheets to suppress restacking and to form conductive pathways, after which NiO was introduced to supply additional redox-active sites while the conductive MXene/CB backbone maintained efficient electron transport. Formation of the composite and its counterparts was verified by physicochemical characterization. In a three-electrode configuration, the tri-material composite exhibits higher current density, longer galvanostatic charge-discharge (GCD) time, and a high areal capacitance (140.18 mF cm −2 ), which is 1.6 times that of MXene/CB (86.72 mF cm −2 ) and 3.4 times that of pristine MXene (40.8 mF cm −2 ). The fabricated ASC device (NiO@MXene/CB//CB) exhibits an areal capacitance of 46.8 mF cm −2 , an energy density of 6.50 μWh cm −2 at a power density of 1.50 mW cm −2 , a device-level rate capability of 69.2%, and a capacitance retention of about 74.5% after 8000 cycles. DFT calculations indicate a NiO-mediated interfacial charge redistribution, consistent with the improved electrochemical performance observed experimentally. This work provides an economically viable route to mitigate two intrinsic limitations of MXene electrodes.