Sustainable Hydrothermal Synthesis of Reduced Graphene Oxide Wrapped on α-MnO2 Nanorod Cathode for Zinc-Ion Batteries

Abstract

Manganese oxide (α-MnO₂) with 1D tunneled cathode material is an attractive option for zinc ion batteries (ZIBs) as it offers high energy efficiency, cost-effectiveness, natural abundance, safety, and environmental friendliness. However, it possesses inferior conductivity, which compromises its electrochemical performance in practical applications. To address this challenge, the integration of reduced graphene oxide is explored, renowned for its excellent conductivity, with α-MnO₂. This integration enhances the stability and conductivity of the composite structure. The reduction of graphene oxide is achieved through a hydrothermal method, facilitating the wrapping of reduced graphene oxide around α-MnO₂ nanorods. This synthesis approach not only saves energy but also aligns with the intended green approach. In this study, the impact of varying the hydrothermal reaction time on the properties of hydrothermally wrapped reduced graphene oxide on 1D α-MnO₂ (HWGOM) is investigated as a cathode material for ZIBs. A series of samples are prepared with hydrothermal reaction times of 4, 6, and 8 h, respectively. Specifically, HWGOM_6 demonstrates a highest specific capacity of 333 mAh g⁻¹ at the current density of 200 mA g⁻¹, along with remarkable cycling stability, retaining 94.3% of its capacity and achieving a coulombic efficiency of 97% over 500 cycles at a constant current density of 500 mA g⁻¹.