Hollow mesoporous hetero-NiCo2S4/Co9S8 submicro-spindles: unusual formation and excellent pseudocapacitance towards hybrid supercapacitors

Abstract

Hierarchical hollow porous architectures with intriguing hetero-interfaces are currently of particular interest in emerging energy-related fields. In this investigation, we report a smart template-free methodology to purposefully fabricate high-quality uniform hollow hetero-NiCo₂S₄/Co₉S₈ (NCCS) submicro-spindles with well-dispersed hetero-nanodomains at the nanoscale. High-yield hollow mesocrystal nickel cobalt carbonate spindles are first solvothermally synthesized as the intermediate, and a subsequent shape-preserving conversion into hetero-NCCS submicro-spindles via a hydrothermal anion-exchange reaction occurs. The underlying template-free formation mechanism of the hollow structures is tentatively proposed. When evaluated as a promising electrode for supercapacitors, the resultant hollow mesoporous hetero-NCCS electrode with a mass loading of 5 mg cm⁻² delivers a good pseudocapacitance of ∼749 F g⁻¹ at a current rate of 4 A g⁻¹, and holds at approximately 620 F g⁻¹ at 15 A g⁻¹ as a result of intrinsic synergetic contributions from structural/compositional/componental merits. Furthermore, an asymmetric device based on hollow mesoporous hetero-NCCS achieves an encouraging energy density of around 33.5 W h kg⁻¹ at a power density of 150 W kg⁻¹, and exceptional cycling behavior with capacitance degradation of ∼0.007% per cycle over 5000 consecutive cycles at 5 A g⁻¹. Comprehensive investigations unambiguously highlight that the unique hollow mesoporous hetero-NCCS submicro-spindles would be a powerful electrode platform for advanced next-generation supercapacitors.