Electrodeposition of Sea Urchin and Cauliflower-like Nickel-/Cobalt-Doped Manganese Dioxide Hierarchical Nanostructures with Improved Energy-Storage Behavior

Transforming the existing Zn-MnO2 primary battery into a secondary battery with enhanced storage behavior and a low cost is of significant interest. Such technology could underpin future energy-storage development. To acquire this, doped electrolytic manganese dioxide (EMD) with hierarchical nano-architectures have been employed as a cathode in the Zn-MnO2 system. EMD is synthesized from manganese sulfate in a sulfuric acid bath with in situ doping of nickel and cobalt ions individually. Sea-urchin-shaped EMD has been obtained with nickel as a dopant, whereas cauliflower-and pyramidal-shaped hierarchical nanostructures are observed with cobalt as a dopant, using a facile galvanostatic method without employing any template or surfactant. The structural studies indicated that all EMD samples (in the absence and presence of dopants) are predominantly composed of gamma-type manganese dioxide; however, the peak intensity increased with increasing concentration of the dopants. The electrochemical results revealed that the Co-doped EMD composite played a crucial role in increasing the storage capacity of the Zn-MnO2 battery, whereas the Ni-doped EMD composite resulted in improved longevity compared the Co-doped and undoped counterparts. The EMD composites individually doped with Ni and Co resulted in improved storage behaviors of 395 and 670 mA h g(-1), respectively, against the undoped sample which is 220 mA h g(-1), implying that the presence of Co3O4 and mesoporous nanostructured surfaces enhanced the fast kinetics of electrochemical reactions.