Fig. 3

a Cyclic voltammograms of 0.5 mM ferrocene carboxylic acid in 0.1 M KCl aqueous solution (pH 7.0) in CASPE-MFD at different scan rates (ascending along the y-axis): 10, 25, 50, 80, 100, 150, 200, 250, 300, and 350 mV/s. b Calibration plots of the anodic (i_pa) and cathodic peak current (i_pc) vs the square scan rate. The two lines represent a linear curve with regression equation, respectively: Y (i_pa) = 0.9932X − 0.2563 (R² = 0.9996, n = 8); Y (i_pc) = − 0.9384X − 0.1774 (R² = 0.9996, n = 8)