High energy and excellent stability asymmetric supercapacitor derived from sulphur-reduced graphene oxide/manganese dioxide composite and activated carbon from peanut shell

Nanorods/fibers, nanosheet and nano-flower like structure were effectively synthesized from sulphur-reduced graphene oxide (RGO-S) and sulphur-reduced graphene oxide/manganese dioxide (RGO-S/MnO₂) composites for supercapacitor applications. Structural, chemical composition and morphological analysis reveal an effective synthesis of the RGO-S and RGO-S/MnO₂ composite. Electrochemical measurements of the optimized mass loading of MnO₂ on RGO-S in a three electrode configurations revealed a specific capacitance of 180.4 F g⁻¹ compared to 75.2 F g⁻¹ of the pristine sample at 1 A g⁻¹ in 2.5 M KNO₃ electrolyte. An assembled asymmetric device consists of optimized RGO-S/MnO₂ as positive electrode and activated carbon from peanut shell (AC-PS) as a negative electrode delivered a high specific energy of 71.74 Wh kg⁻¹ with its corresponding specific power of 850 W kg⁻¹ at 1 A g⁻¹. It was observed that even at high specific current of 5 A g⁻¹ the device was able to maintain a specific energy of 55.30 Wh kg⁻¹. An excellent stability with capacitance retention of 94.5% and columbic efficiency of 99.6% up to 10, 000 cycles was recorded for the device at 5 A g⁻¹. The device demonstrated a very good stability after being subjected to a voltage holding of up to 90 h and an outstanding self-discharge of about 1.45 V was recorded within the first 10 h and 1.00 V after 72 h from its maximum potential of 1.7 V.