Fig. 3

Charge–discharge (a, c) and CV (b, d) curves of the PPy, PPy-COOH (a, b), PTp, and PTp-COOH (c, d) nanostructures from the second cycle. The current density was 20 mA g–1 for the charge–discharge measurements. The scan rate was 1 mV s–1 on the CV curves. The charge–discharge curves of the first cycle and the reproducibility of the x values are shown in Figure S3 and Table S4 in the Supplementary Information