Controlling surface oxygen vacancies in 3D networked MnO2 based nanocomposites for high performance flexible in-plane micro-supercapacitors

The rising demand for portable, flexible, and eco-friendly electronic devices has spurred the development of micro-supercapacitors (mSCs) as compact and versatile energy storage components. Electric double-layer (EDL)-mSCs incorporating graphene electrodes offer swift and reversible charge/discharge processes, making them suitable for sustainable device systems. To greatly enhance the electrochemical performance of mSCs, we present a direct synthesis and fabrication of surface oxygen vacancy-controlled MnO2 with a Faradaic capacitive behavior on a porous graphene electrode with 3D networked framework. Surface oxygen vacancies in MnO2 were created through hydrogen peroxide (H2O2) treatment, which led to an increase in the electrode's conductivity and facilitating electrochemical reactions due to creation of the local electric field at the vacancy sites. We achieved 251 % and 163 % increase in capacitance of surface oxygen vacancy controlled MnO2/graphene nanocomposite electrode compared to the porous graphene electrode and pristine MnO2/graphene electrode, respectively, and exhibited a volumetric energy density of 3.61 Wh/L. Furthermore, the mSCs demonstrated excellent cyclic stability and mechanical flexibility under various strain conditions. This surface oxygen vacancy-controlled MnO2/graphene nanocomposite electrode represents a simple and efficient strategy for high-performance and versatile energy storage components, with potential applications in electronic devices and sustainable energy systems.