Hierarchical design of Co-CH/NiCo2S4/Co9S8 hollow dodecahedron supercapacitors with tunable energy storage kinetics for improved stability and large energy density

Supercapacitors with high energy density and long serving life is highly desirable for solving the energy crisis. Herein, we propose a simple strategy to fabricate hollow cobalt metal-organic framework dodecahedron heterostructures composed of Co(CO3)0.5OH·0.11H2O [Co-CH], NiCo2S4 and Co9S8 with controllable energy storage kinetics. The decoration of NiCo2S4 nanosheets provides a 6.1-fold higher specific capacity (1011.0 C g−1 at 1 A g−1) than Co9S8. The electrochemical kinetic analysis reveals that the OH- dissociation process plays a decisive role in the structural stability. Surface-loaded pseudo-capacitive materials can promote the reversibility of Faraday redox reaction and OH- diffusion coefficient. Controlled growth of Co-CH nano-needles reduces the diffusion-dominated process and improve the cycling stability by a factor of 4.0–5.8 due to the increased reaction reversibility, charge transfer and OH- diffusion. The two-electrode asymmetric device displays a high energy density of 47.6 W h kg−1 at a power density of 800 W kg−1 and good cycling stability (78.1 % retention after 5000 cycles at 5 A g−1). This work offers an effective approach for fabricating low-cost transition metal complexes that hold great promise for practical energy storage applications.