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Two-dimensional (2D) Co 3 O 4 thin sheets assembled by 3D interconnected nanoflake array framework structures were first synthesized from nanoflake array-assembled porous cobalt-oxalate coordination complex thin sheets by means of direct pyrolysis in the air and the synthesis is simple and facile to implement scale-up for various application. The products exhibit excellent pseudocapacitive performance in an alkaline medium, holding great promise in supercapacitors (SCs). The electrochemical properties of the obtained Co 3 O 4 thin sheets were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge measurement (CP) and electrochemical impedance spectroscopy (EIS) in 2.0 M KOH solution. Temperature has an obvious effect on the performance of the products. Impressively, the thin sheets synthesized at 500 °C for 6 h used as electrode materials for SCs exhibit a specific capacitance as high as 1500 F g −1 at 1 A g −1 and even 828 F g −1 at 10 A g −1 , as well as remarkable cycling stability with 99.3% of its initial capacitance retained after 2000 continuous charge–discharge cycles at a current density of 5 A g −1 . In addition, the assembled asymmetric system using the obtained Co 3 O 4 thin sheets at 500 °C for 6 h as positive electrode and activated carbon as negative one can produce a high energy density of 15.4 Wh kg −1 at a power density of 0.8 kW kg −1 . The hierarchical architectures of the products with hierarchical porosity and interconnected channels as well as the synergistic effect between their compositions provide several advantages including a large contact surface area, short ion diffusion path and good charge transport, which validate these thin sheets promising potential for a wide range of applications in energy storage. [ABSTRACT FROM AUTHOR]