Fig. 6
a Cyclic voltammograms of the various samples, recorded at 5 mV s−1. b Specific capacitances of the samples, determined at scan rates from 5 to 500 mV s−1. c Galvanostatic charge/discharge curves recorded at 0.1 A g−1. d Nyquist plots of the samples measured from 100 mHz to 100 kHz; inset: corresponding expanded high-frequency region of the plots