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Abstract
Ionic transport within porous carbon electrodes is crucial for optimizing charge/discharge rates in supercapacitors, yet the material properties governing ion dynamics remain poorly understood. Contrary to the traditional viewpoint, we find that mesoporosity does not necessarily correlate with high supercapacitor rate capability. Instead, we employed pulsed field gradient nuclear magnetic resonance to directly measure anionic effective diffusivities in the carbon pores, offering a probe of ionic transport in supercapacitors. Our findings reveal a significant discrepancy between short-range and long-range diffusivities, which captures the tortuosity of the pore network. Short-range diffusivities lack correlation with supercapacitor rate capability, whereas long-range diffusivities correlate strongly. Ultimately, low-tortuosity nanoporous carbons exhibited superior rate capability, highlighting the importance of well-interconnected pore networks for efficient ion transport. Our study reveals pore network tortuosity as a key factor that governs charging rates in amorphous nanoporous carbons and guides the design of electrodes with optimized transport channels to enhance supercapacitor performance.
Supplementary materials
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Supplementary information
Description
Figure S1 Supercapacitor rate capability measured across various nanoporous carbons and electrolytes
Figure S2 N2 physisorption isotherms and pore size distribution plots
Figure S3 Dependence of 19F PFG diffusion coefficient on diffusion time for 1 M TEA-BF4 in acetonitrile.
Figure S4 Calculated root mean square (RMS) displacements in the direction of the gradient axis
Figure S5 19F NMR spectra of nanoporous carbons soaked in 1M electrolyte
Figure S6-7 19F NMR spectra of nanoporous carbons soaked in 1M electrolyte compared to the first slice of PFG diffusion measurements
Figure S8 19F in pore Diffusion measurements
Figure S9: Scanning Electron Microscopy (SEM) images of carbon films, powders and cloths
Figure S10: Comparison between carbons films (5wt% PTFE) and powders
Figure S11 Correlations between capacitance, microporous and mesoporous SSA with diffusion coefficients and tortuosity
Figure S12 Tortuosity measurement: diffusion coefficients vs diffusion time
Figure S13: Galvanostatic charge−discharge plots and cyclic voltammograms
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