Achieving Ultrahigh Volumetric Performance of Graphene Composite Films by Outer-Inner Space Dual Utilizing Strategy

Graphene film often suffers from the low gravimetric capacitance at the situation of high density due to the low space utilization, resulting in an undesirable volumetric performance. Herein, an outer-inner space dual utilizing strategy is reported to fabricate high density yet high gravimetric performance polydopamine coated dopamine/reduced graphene oxide composite film (DA/rGO@PDA). The DA molecule is introduced into inner area of graphene film as a redox-active spacer, which endows electrode with additional pseudocapacitance, favorable ion accessible area as well as accelerated ion diffusion kinetics. More importantly, the outer surface of graphene composite film is covered by the polydopamine layer formed during hydrothermal process, which is demonstrated to be a pseudocapacitance donor. Consequently, the outer surface and inner space of DA/rGO@PDA film was ultilized simutaneously, which is rarely reported in the previous research. Benefiting from the ingenious structure design, the DA/rGO@PDA delivers a high gravimetric capacitance of 449.3 F g-1 at a high density of 1.72 g cm-3, corresponding to an ultrahigh volumetric performance of 772.8 F cm-3. Moreover, the symmetric supercapacitor exhibits an excellent volumetric energy density (16.4 Wh L-1) and cycle stability (90% of its initial capacitance after 5000 cycles at 5 A g-1) in aqueous electrolyte. The outer-inner space dual utilizing strategy promotes new opportunities for paper-like monoliths as energy storage electrode materials.