Morphology-driven interlinked 2D nanostructures anchored nickel cobalt sulfide (NiCo2S4) electrodes for high-performance symmetric supercapacitor

Abstract

Nickel cobalt sulfide (NiCo<inf>2</inf>S<inf>4</inf>; NCS) is known for its notable inherent electronic conductivity and high theoretical capacity, attributed to its excellent redox behavior. However, developing well-defined hierarchical nanostructured NCS with ample electroactive interfaces remains a persistent challenge. In this study, we report reaction time-dependent hydrothermal synthesis of NCS nanoparticles, which transform into nanoflakes under controlled reaction conditions. With extended reaction duration, these nanoflakes further interlinked to form hierarchical discs and micro-flowers like morphologies. The cubic crystalline NCS nanostructures with larger specific surfaces and Ni2+/Ni3+, Co3+/Co2+, and S2− oxidation states exhibit remarkable electrochemical redox activity in alkaline electrolyte. NCS micro-flowers composed of interlinked 2D nanoflakes (NCS10) exhibit specific capacitance (C<inf>s</inf>) of 1062.7 F g−1 at current density of 1 A g−1 and C<inf>s</inf> retention of 93.5 % after continuous 5000 GCD cycles in three-electrode configuration. When employed in a symmetric solid-state battery-type supercapacitor, the NCS10 electrode delivered C<inf>s</inf> of 72.52 F g−1 at 1 A g−1 and maximum energy density (E<inf>d</inf>) of 17.02 Wh kg−1 and power density (P<inf>d</inf>) of 5.02 kW kg−1. The 2-electrode device also offered satisfactory long-term stability with 86.27 % retention after 1000 cycles. Our study elucidates the critical role of morphology in enhancing the electrochemical performance of Ni-Co sulfide electrodes, highlighting their real-time potential for high-performance supercapacitors. © 2025 Elsevier B.V., All rights reserved.