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Flexible asymmetric supercapacitors (ASCs) are promising energy storage devices as they provide much higher energy density and wider applications than symmetric or nonflexible supercapacitors. While various positive electrode materials have been demonstrated with good performances, suitable and matching negative electrode materials are still desperately needed. In this work, Fe 2 O 3 nanoparticle clusters are rationally coupled with reduced graphene oxide (rGO) sheets, leading to a highly flexible thin paper with excellent mechanical stability and electrical conductivity. The well dispersed and porous Fe 2 O 3 nanoparticle clusters are composed of much smaller nanoparticles (∼30 nm), which provide a large electrode−electrolyte interface. When tested in 3 M KOH aqueous electrolyte, the hybrid Fe 2 O 3 nanoparticle clusters/rGO paper demonstrates much improved volumetric capacitance in the negative voltage range, compared to pristine rGO paper (178.3 compared to 106.2 F cm −3 at 1 mV s −1 scan rate in cyclic voltammetry test). In addition, when assembled into ASC, both high volumetric energy and power density are obtained (0.056 Wh cm −3 and 6.21 W cm −3 ), which are much higher compared with that of the ASC used rGO paper as the negative electrode. The systematic investigations in understanding the synergistic effects of electrochemical behavior between the Fe 2 O 3 nanoparticle clusters and rGO paper provide insights to future hybrid-type supercapacitor design.

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