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

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 degrees C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (S-BET) of CZMOF2 was similar to 2700 m(2) g(-1), much higher than that of CZMOF1 (similar to 1300 m(2) 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 degrees C, pore generation is dominated by the Zn/C ratio of ZMOFs, as carbon atoms reduce the zinc oxides formed during carbonization. Above 1000 degrees 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.

Automated summary

Heat treatment of metal-organic frameworks (MOFs) can produce functional carbons suitable for supercapacitor electrodes. This study investigated the carbonization process of two zinc-based MOFs and found that pore generation is crucial for achieving high capacitance. The findings provide valuable insights for the development of other metal-based MOF-derived multifunctional carbons.