Morphology controlling of manganese-cobalt-sulfide nanoflake arrays using polyvinylpyrrolidone capping agent to enhance the performance of hybrid supercapacitors

Transition metal sulfide-based electrode materials are promising candidates for energy storage applications owing to their richer redox-active sites and higher electrical conductivity than their oxide counterparts. Manganese-cobalt-sulfide (MCS) nanoflakes were synthesized on nickel foam in the presence of polyvinylpyrrolidone (PVP) as a capping agent using a one-step hydrothermal method. The variation in the amount of PVP in the reaction solution had a prominent impact on the MCS electrode morphology. PVP altered the morphology of the MCS nanoflakes. Different shapes of interconnecting-nanoflake arrays were formed with different amounts of PVP. The MCS electrode prepared using 0.2 g of PVP (MCS-P2) showed the best efficiency with a specific capacity of 1312 C g-1 (3215 F g-1) at 1 A g-1 and still retained a remarkable capacity of 1000 C g-1 (2480 F g-1) at 20 A g-1. Moreover, the hybrid supercapacitor (HS) device consisting of MCS-P2//reduced graphene oxide (rGO) revealed a high energy density of 48.7 Wh kg-1 at a corresponding power density of 386 W kg-1. Even at a higher power density of 10.8 kW kg-1, a notable energy density of 25.5 Wh kg-1 was retained. These remarkable results highlight the potential applications of the MCS-P2 electrode material in energy storage.