Defect-free low-fluorine MXenes (Nb 2 CT x /V 2 CT x ) via time-optimized HF etching: achieving superior conductivity and ultrahigh capacitance for supercapacitors

A time-optimized HF etching strategy yields few-layer MXene nanosheets with suppressed defects and minimized fluorine. The Nb 2 CT x exhibits ultrahigh conductivity (5530 S m −1 ) and volumetric capacitance (1989.57 F cm −3 at 2 mV s −1 ).