Effect of reaction time and PVP contents on morphologies of hierarchical 3D flower‐like ZnCo 2 O 4 microstructures for energy storage devices

Summary Hierarchical 3D flower‐like ZnCo 2 O 4 (ZCO) microstructures assembled from petal‐like nanosheets/flakes of non‐uniform sizes were engineered by a polyvinylpyrrolidone (PVP)‐assisted hydrothermal method. Four different samples/morphologies of ZCO were obtained (PVP‐L@6, PVP‐H@6, PVP‐L@12, and PVP‐H@12) by altering the reaction parameters such as surfactant concentration (PVP) and reaction time, which can play a significant role in the formation of flower‐/petal‐/flake‐like architectures. The alteration of the reaction parameters not only resulted in morphological changes but also affected the surface area, pore size/volume, crystalline nature, non‐stoichiometry of Zn, Co, and O in ZCO, and their electrochemical performance. The metal (Zn/Co)/O deficiencies of ZCO samples were investigated via X‐ray photoelectron spectroscopy and supported by the Rietveld refinement method. Furthermore, a plausible growth mechanism for these flower‐like ZCO microstructures was projected based on the experimental results. The four dissimilar samples/morphologies of ZCO, which exhibit different electrochemical performances, were investigated. Our results show that PVP‐H@12 exhibits higher specific capacitance (761/680 F g −1 at 0.35/1 A g −1 ) and good cycling constancy (90% capacitive retention after 2000 cycles at 5 Ag −1 ) among all the four samples.