Many scientists are interested in developing supercapacitors, which have electrolyte rather than solid dielectric between the charged plates. In the field of electrochemistry, cyclic voltammetry (CV) is often used to determine the capacitance of electrodes (e.g., carbon-based electrodes) in supercapacitors.
I have often heard that an ideal capacitor gives rise to a rectangular cyclic voltammogram (CV). Can you please help me understand why this is the case? In other words, why does an ideal capacitor reach a constant current I as soon as a voltage V is applied?
I indeed see nearly ideal CVs in many literature articles (CVs which are rather rectangular with rounded corners). In other figures, though, I see relative deviation from "rectangles with rounded corners," in that I see abrupt peaks, spikes, or valleys.
For example, below I have plotted two figures from Khomenko, Electrochimica Acta 2005, 50, 2499-2506. Just very roughly and "hand wavy," what might be the qualitative reason for the "rectangle with rounded corners" behavior of Figure 8 (left) and the "abrupt peaks" behavior of Figure 4 (right)? Could it be that the sample in Figure 8 (left) is relatively unreactive toward apllied potential, whereas the sample in Figure 4 (right) undergoes redox (Faradaic) reactions -- indicating the presence of so-called pseudocapacitance -- when an external potential is applied?
Please know that I am not looking for an answer specific to the article to which I linked. I am only asking this question in the context of basic, qualitative aspects of cyclic voltammetry. Thanks!