Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework

Nanoporous carbon and nanoporous cobalt oxide (Co₃O₄) materials have been selectively prepared from a single metal-organic framework (MOF) (zeolitic imidazolate framework, ZIF-67) by optimizing the annealing conditions. The resulting ZIF-derived carbon possesses highly graphitic walls and a high specific surface area of 350 m²·g^-1, while the resulting ZIF-derived nanoporous Co₃O₄ possesses a high specific surface area of 148 m²·g^-1 with much less carbon content (1.7 at%). When nanoporous carbon and nanoporous Co₃O₄ were tested as electrode materials for supercapacitor application, they showed high capacitance values (272 and 504 F·g^-1, respectively, at a scan rate of 5 mV·s^-1). To further demonstrate the advantages of our ZIF-derived nanoporous materials, symmetric (SSCs) and asymmetric supercapacitors (ASCs) were also fabricated using nanoporous carbon and nanoporous Co₃O₄ electrodes. Improved capacitance performance was successfully realized for the ASC (Co₃O₄//carbon), better than those of the SSCs based on nanoporous carbon and nanoporous Co₃O₄ materials (i.e., carbon//carbon and Co₃O₄//Co₃O₄). The developed ASC with an optimal mass loading can be operated within a wide potential window of 0.0-1.6 V, which leads to a high specific energy of 36 W·h·kg^-1. More interestingly, this ASC also exhibits excellent rate capability (with the highest specific power of 8000 W·kg^-1 at a specific energy of 15 W·h·kg^-1) combined with long-term stability up to 2000 cycles.