Controllable fabrication of 2D and 3D porous graphene architectures using identical thermally exfoliated graphene oxides as precursors and their application as supercapacitor electrodes

Abstract

Improving the energy density of graphene-based electrical double-layer capacitors (EDLCs) with excellent rate capability requires a delicate construction to both ion-accessible surface and spatial architecture of graphene. In this work, two-dimensional (2D) and three-dimensional (3D) porous graphene architectures are controllably fabricated by two activation approaches (KOH, CO2) using identical thermally exfoliated graphene oxides as precursors and employed for systematically unravelling the governing principles of structural characteristics toward the corresponding supercapacitive performances. Under optimal conditions, the KOH-activated graphene appears as 2D lamellas with a bimodal micro-mesopore distribution and an ultra-high specific surface area of 2518 m2g-1, which gives a specific capacitance of 261 F g−1 and a capacitance retention of 98.5% at 5 A g−1 after 1000 cycles. In contrast, CO2-activated graphene shows 3D curly morphology with a hierarchical micro-meso-macroscopic structure and an ultra-large pore volume of 3.08 cm3g-1, where an excellent rate capability of 86.1% from 0.5 to 10 A g−1 can be implemented. It is demonstrated that the microporosity, specific surface area and surface wettability are the key factors to the capacitance, while the pore morphology and topology is responsible to the rate performances. Our results may offer critical insights into the rational design of activated graphene for supercapacitors.