Fig. 4

Ultra-fast electron and ion transport in the PCF-based electrodes. a Nyquist plots collected at open circuit potentials with 5 mV perturbation and a frequency range from 10,000 to 0.1 Hz. The open symbols are experimental data and the solid lines are fitting curves. b Z’ vs. the reciprocal of the square root of frequency (ω^−0.5) in the intermediate frequency range. The dashed lines are best fitting lines to calculate the diffusion resistance, σ. c The ion diffusion resistance of the carbon fiber electrodes in comparison with other reported electrodes: (I) Ref. 57; (II) Ref. 58; (III) Ref. 59. The CF-based electrodes show low diffusion resistance and the PCF-based electrodes show ultra-low diffusion resistance