Zinc‐Based Metal–Organic Frameworks for High‐Performance Supercapacitor Electrodes: Mechanism Underlying Pore Generation

Abstract

Heat treatment of metal–organic frameworks (MOFs) has provided a wide variety of functional carbons coordinated with metal compounds. In this study, two kinds of zinc‐based MOF (ZMOF), C16H10O4Zn (ZMOF1) and C8H4O4Zn (ZMOF2), were prepared. ZMOF1 and ZMOF2 were carbonized at 1000 °C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (SBET) of CZMOF2 was ~2700 m2 g−1, much higher than that of CZMOF1 (~1300 m2 g−1). A supercapacitor electrode based on CZMOF2 achieved specific capacitances of 360, 278, and 221 F g−1 at 50, 250, and 1000 mA g−1 in an aqueous electrolyte (H2SO4), respectively, the highest values reported to date for ZMOF‐derived electrodes under identical conditions. The practical applicability of the CZMOF‐based supercapacitor was verified in non‐aqueous electrolytes. The initial capacitance retention was 78% after 100 000 charge/discharge cycles at 10 A g−1. Crucially, the high capacitance of CZMOF2 arises from pore generation during carbonization. Below 1000 °C, pore generation is dominated by the Zn/C ratio of ZMOFs, as carbon atoms reduce the zinc oxides formed during carbonization. Above 1000 °C, a high O/C ratio becomes essential for pore generation because the oxygen functional groups are pyrolyzed. These findings will provide insightful information for other metal‐based MOF‐derived multifunctional carbons.