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 °C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (S_BET) 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.