The morphology comprises of nano-rods/fibers, nano-sheet and nano-flower like structure were successfully produced from sulphur reduced graphene oxide/manganese dioxide composite for ultracapacitor application. The electrochemical evaluations of the optimal sample presented a specific capacitance of 180.40 F g^-1 at 1 A g^-1 in 2.5 M KNO₃ electrolyte in a three-electrode set-up. An asymmetric device made up of sulphur reduced graphene oxide/manganese dioxide composite and activated carbon as a positive and negative electrode, respectively, delivered a high specific energy and power of 71.74 Wh kg^-1 and 850 W kg^-1 at 1 A g^-1. It was further noticed that the device was able to retain a specific energy of 55.30 Wh kg^-1 even at high specific current of 5 A g^-1. An outstanding cycling stability with a capacitance retention of 94.5 % and energy efficiency of 99.9 % for up to 10,000 cycles was noted at 5 A g^-1. The device revealed an excellent stability after being subjected to a voltage holding of up to 90 h and an exceptional self-discharge of about 1.45 V was recorded within the first 10 h and 1.00 V after 72 h from its maximum voltage of 1.7 V. The results obtained confirms that the produced material offers a great potential for the application of high energy density supercapacitor.

Keywords: Graphene oxide; Energy density; Supercapacitor; Shuttle effects; Composite materials; Sulphur.