Interfacial assembly of 2D polydopamine/graphene heterostructures with well-defined mesopore and tunable thickness for high-energy planar micro-supercapacitors

Two-dimensional (2D) mesoporous pseudocapacitive polymer/graphene heterostructures combine the advanced merits of 2D materials and mesoporous materials, possessing unique nanosheet structure, large specific surface area (SSA), abundant oxygen/nitrogen-containing groups, desirable electrical conductivity and admirable electrochemical redox activity, and hold great potential for constructing high-performance planar micro-supercapacitors (MSCs). Herein, we demonstrate the interfacial assembly of 2D mesoporous polydopamine/graphene (mPDG) heterostructures with well-defined mesopore structure (12 nm) and adjustable thickness (7.5-14.1 nm) for planar high-energy pseudocapacitive MSCs. Attributed to medium thickness, exposed mesopore of 12 nm and large SSA of 108 m2/g, the mPDG with 10.8 nm thickness reveals prominent mass capacitance of 419 F/g and impressive cycling stability with ∼96% capacitance retention after 5000 cycles. Furthermore, the symmetric mPDG-based MSCs with “water-in-salt” gel electrolyte present wide voltage window of 1.6 V, superior volumetric energy density of 11.5 mWh/cm3, outstanding flexibility and self-integration ability. Therefore, this work offers a new platform of controllably synthesizing 2D mesoporous heterostructures for high-performance MSCs.