Enhanced performance of hybrid supercapacitors by the synergistic effect of Co(OH)2 nanosheets and NiMn layered hydroxides.

A self-supporting composite electrode material with a unique three-dimensional structure was synthesized by in-situ growth of nanoscale NiMnLDH-Co(OH)2 on a nickel foam substrate via hydrothermal electrodeposition. The 3D layer of NiMnLDH-Co(OH)2 provided abundant reactive sites for electrochemical reactions, ensuring a solid and conductive skeleton for charge transfer and resulting in significant enhancement of electrochemical performance. The composite material showed a strong synergistic effect between the small nano-sheet Co(OH)2 and NiMnLDH, which promoted reaction kinetics, while the nickel foam substrate acted as a structural conductivity agent, stabilizer, and good conductive medium. The composite electrode showed impressive electrochemical performance, achieving a specific capacitance of 1870F g-1 at 1 A g-1 and retaining 87% capacitance after 3000 charge-discharge cycles, even at a high current density of 10 A g-1. Moreover, the resulting NiMnLDH-Co(OH)2//AC asymmetric supercapacitor (ASC) demonstrated remarkable specific energy of 58.2 Wh kg-1 at a specific power of 1200 W kg-1, along with outstanding cycle stability (89% capacitance retention after 5000 cycles at 10 A g-1). More importantly, DFT calculations reveal that NiMnLDH-Co(OH)2 facilitates charge transfer, accelerating surface redox reactions and increasing specific capacitance. This study presents a promising approach towards designing and developing advanced electrode materials for high-performance supercapacitors.