Coupling W 18 O 49 /Ti 3 C 2 T x MXene Pseudocapacitive Electrodes with Redox Electrolytes to Construct High-Performance Asymmetric Supercapacitors.

A pseudocapacitive electrode with a large surface area is critical for the construction of a high-performance supercapacitor. A 3D and interconnected network composed of W 18 O 49 nanoflowers and Ti 3 C 2 T x MXene nanosheets is thus synthesized using an electrostatic attraction strategy. This composite effectively prevents the restacking of Ti 3 C 2 T x MXene nanosheets and meanwhile sufficiently exposes electrochemically active sites of W 18 O 49 nanoflowers. Namely, this self-assembled composite owns abundant oxygen vacancies from W 18 O 49 nanoflowers and enough active sites from Ti 3 C 2 T x MXene nanosheets. As a pseudocapacitive electrode, it shows a big specific capacitance, superior rate capability and good cycle stability. A quasi-solid-state asymmetric supercapacitor (ASC) is then fabricated using this pseudocapacitive anode and the cathode of activated carbon coupled with a redox electrolyte of FeBr 3 . This ASC displays a cell voltage of 1.8 V, a capacitance of 101 F g -1 at a current density of 1 A g -1 , a maximum energy density of 45.4 Wh kg -1 at a power density of 900 W kg -1 , and a maximum power density of 18 000 W kg -1 at an energy density of 10.8 Wh kg -1 . The proposed strategies are promising to synthesize different pseudocapacitive electrodes as well as to fabricate high-performance supercapacitor devices.