MnCO3 on Graphene Porous Framework via Diffusion-Driven Layer-by-Layer Assembly for High-Performance Pseudocapacitor.

Diffusion-driven layer-by-layer (dd-LbL) assembly is a simple yet versatile process that can be used to construct graphene oxide (GO) into a three-dimensional (3D) porous framework with good mechanical stability. In particular, the oxygen functional groups on the GO surface are well retained, providing nucleation sites for further chemical reactions to be performed upon. Therefore, such a scaffold should serve as a promising starting material for creating a wide range of 3D graphene-based composites while maintaining a high accessible surface area. Herein, we demonstrate the use of the porous GO macrostructure derived from dd-LbL assembly for the preparation of graphene-MnCO3 hybrid structures. MnCO3 is a newly reported pseudocapacitive material for supercapacitors; however, its electrochemical performance is hampered by its low electrical conductivity and poor chemical stability. Through reaction between KMnO4 and GO during a hydrothermal process, the surface of the porous scaffold was rendered with uniform MnCO3 nanoparticles. With the reduced graphene oxide (rGO) sheets serving as the conductive backbone, the resultant MnCO3 nanoparticles exhibited a capacitance of 698 F g-1 at a charge/discharge current of 0.5 mA (320 F g-1 for the combined rGO and MnCO3 composite). Furthermore, the electrode maintained 77% of its initial capacity even after 5000 cycles of charge/discharge tests at 20 mA.