Facile Synthesis of Three-Dimensional Sandwiched MnO₂@GCs@MnO₂ Hybrid Nanostructured Electrode for Electrochemical Capacitors

Designable control over the morphology and structure of active materials is highly desirable for achieving high-performance devices. Here, we develop a facile microwave-assisted synthesis to decorate MnO₂ nanocrystals on three-dimensional (3D) graphite-like capsules (GCs) to obtain sandwich nanostructures (3D MnO₂@GCs@MnO₂) as electrode materials for electrochemical capacitors (ECs). A templated growth of the 3D GCs was carried out via catalytic chemical vapor deposition and MnO₂ was decorated on the exterior and interior surfaces of the GC walls through microwave irradiation to build an engineered architecture with robust structural and morphological stability. The unique sandwiched architecture has a large interfacial surface area, and allows for rapid electrolyte diffusion through its hollow/open framework and fast electronic motion via the carbon backbone. Furthermore, the tough and rigid nature of GCs provides the necessary structural stability, and the strong synergy between MnO₂ and GCs leads to high electrochemical activity in both neutral (265.1 F/g at 0.5 A/g) and alkaline (390 F/g at 0.5 A/g) electrolytes. The developed hybrid exhibits stable capacitance up to 6000 cycles in 1 M Na₂SO₄. The hybrid is a potential candidate for future ECs and the present study opens up an effective avenue to design hybrid materials for various applications.