In-situ synthesis of carbon nanotube/graphene composite sponge and its application as compressible supercapacitor electrode

•Carbon nanotube/graphene (CNT/G) composite sponges are synthesized by a simple, in-situ unzipping method.•Polypyrrole is electro-polymerized onto the sponge to form CNT/G/polypyrrole (CNT/G/PPy) composite sponge.•The specific capacitance is improved from 4 to 225 F/g for the CNT/G/PPy composite.•The CNT/G/PPy sponge retains the internal conductive network and exhibits excellent capacitive performance.

ABSTRACTCarbon nanotube/graphene (CNT/G) composite sponge is prepared by in-situ partially unzipping of CNT sponge. Polypyrrole is then electro-polymerized onto the sponge to form CNT/graphene/polypyrrole (CNT/G/PPy) ternary composite sponge. The capacitive behavior of the composite is investigated by using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results show that the degree of unzipping of CNT can be controlled by regulating the period of reaction. The specific capacitance of CNT/G sponge shows a significant improvement compared to that of the original CNT sponge (from 4 to 103 F/g). With PPy coating, the CNT/G/PPy displays a high specific capacitance of 225 F/g and excellent capacitance retention of 90.6% after 1000 cycles. In addition, the CNT/G/PPy sponge shows a high capacitance performance under compression. This work indicates that it is possible to build high performance compressive electrodes using CNT/G core networks coated with conductive polymer.

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