Ionic liquid-assisted pore masking reveals kinetic limitations of micropore utilization in carbon nanofiber/MnO2 supercapacitors

초록

The role of micropores in electric double-layer capacitance remains under debate, particularly in terms of their effective utilization and rate-dependent behavior. In this study, micropore-driven capacitance is systematically investigated using hierarchically porous hollow carbon nanofiber/MnO2 composites (HCFs/MnO2) with controlled microporosity. Nitrogen-rich hollow carbon nanofibers are fabricated via dual-nozzle electrospinning, followed by KOH activation to introduce microporosity. A temporary ionic liquid-assisted pore masking strategy is employed to preserve micropores during MnO2 incorporation, enabling the formation of micropore-rich composites while maintaining hierarchical pore structures. By comparing electrochemical behavior in aqueous and non-aqueous electrolytes, we show that the contribution of micropores to capacitance strongly depends on ion size and transport kinetics. The capacitance normalized by surface area increases with micropore fraction, indicating enhanced charge storage efficiency. However, this enhancement is significantly suppressed at high scan rates, suggesting limited ion accessibility within micropores. These results demonstrate that microporeinduced capacitance is not solely determined by surface area, but is strongly influenced by kinetic constraints associated with ion transport. This study provides experimental insight into the rate-dependent role of micro-porosity and highlights the importance of balancing micropore contribution and ion transport in designing highperformance supercapacitor electrodes.

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