Petal-inspired zinc cobaltite with cubic spinel structure: Surface-modified tremella flower for high-efficiency hybrid energy storage

In this investigation, modulating the morphological structure of oxide metals strategically has consistently directly impacted the electrochemical characteristics of redox reactions in energy storage applications. Microstructures that are hollow and porous are very intriguing materials for energy storage devices, especially supercapacitors, and enhance the properties of their applications. The unique tremella-like hierarchical microsphere of ZnCo₂O₄ (H3-ZC) has successfully synthesized morphological variation with porous and higher surface area. The same method is followed by an ultrathin hierarchical nanosheet of Co₃O₄ (H1-C) and nanorod with hexagonal bodies of ZnO (H2-Z). Crystal structure, packing factor calculation, and electrochemical investigations have been verified for the synthesized nanomaterials. The H3-ZC exhibited improved electrochemical performance without the addition of impurities. It has superior specific capacitance and cycling stability, achieving a specific capacitance of 1232 F g⁻¹ in 1 M KOH at a current density of 1 A g⁻¹. It exhibited excellent cycling stability, retaining 93 % of its capacitance after 5000 cycles, with a low charge resistance of 0.8 Ω. The H3-ZC-ASC hybrid capacitor was created by combining activated carbon (AC) with H3-ZC. This device achieved an impressive specific capacitance of 183.1 F g⁻¹ at a current density of 1 A g⁻¹. It delivered an energy density of 234.3 W h kg⁻¹ at a power density of 4608 kW kg⁻¹. This result indicates that the tremella flower-like microsphere exhibits greater supercapacitor performance.