Pajkossy and Kolb extracted C dl from electrochemical impedance spectroscopy (EIS) data using the Frumkin-Melik-Gaikazyan model. Xue et al. extracted C dl from EIS data using an electric circuit model involving empirical constant phase elements. Ojha et al. calculated C dl from cyclic voltammogram (CV) data. Generally, EIS is more accurate than CV in determining C dl , because EIS can separate C dl from possible pseudo-capacitances of chemisorption. In comparison, C dl calculated from CV includes everything, which can explain the fact why the value in the study of Ojha et al. is several orders higher than the values reported by other two groups.