Figure 4. Electrochemical performance of the carbon microspheres.

(a) galvanostatic charge/discharge curves of CM-NFs samples in 1 M H₂SO₄ solution with different current densities; (b) CV curves of CMs, CM-Ns and CM-NFs samples in 1 M H₂SO₄ solution at a scan rate of 10 mV s⁻¹; (c) corresponding capacity retentions at the current density from 0.1 to 5 A g⁻¹; and (d) stability evaluation of the CM-NF electrodes in 1 M H₂SO₄ solution at a charge current of 5 A g⁻¹ for the 10,000 cycles.