Regulating Voltage Window and Energy Density of Aqueous Asymmetric Supercapacitors by Pinecone‐Like Hollow Fe2O3/MnO2 Nano‐Heterostructure

Abstract Aqueous asymmetric supercapacitors (ASCs) are promising candidates for energy storage device because of their advanced merits of high power density, long cycling life, nontoxicity, and low cost. However, the energy density of the aqueous ASCs is still limited by the low operating voltage windows and the unmatchable capacitances of cathode and anode. Herein, pinecone‐like hollow Fe 2 O 3 /MnO 2 nano‐heterostructures (Fe 2 O 3 /MnO 2 NHs) cathode is developed with high potential window (0–1.2 V) and specific capacitance (297 F g −1 at 1 A g −1 ). Owing to the opposite operating voltage windows and similar capacitances value of the Fe 2 O 3 /MnO 2 NHs as cathode and reduced graphene oxide/Fe 2 O 3 (rGO/Fe 2 O 3 ) aerogels as anode (−1.1 to 0 V, 274 F g −1 at 1 A g −1 ), the assembled Fe 2 O 3 /MnO 2 //rGO/Fe 2 O 3 aqueous ASCs deliver a wide voltage window up to 2.4 V and a high energy density of 57.0 Wh kg −1 . The as‐fabricated ASC also presents outstanding cycling stability (with 88.9% retention after 10 000 cycles at 10 A g −1 ) and well rate performance. Moreover, Fe 2 O 3 /MnO 2 //rGO/Fe 2 O 3 all‐solid‐state ASC exhibits excellent voltage window (2.3 V), capacitance, and ratability. Thus, this study provides a novel approach for constructing high‐voltage aqueous ASC with high energy density.