Impurities Limit the Capacitance of Carbon Based Supercapacitors

09 October 2018, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


Supercapacitors cannot fulfill their potential as energy storage devices without substantially improving their comparatively low energy density. This requires improving their capacitance. Unfortunately, predicting the capacitance of the carbon-based materials that typically make up supercapacitor electrodes is difficult. For example, remarkably we lack a theoretical understanding of the capacitance of even the most basic example of a carbon electrode: highly oriented pyrolytic graphite. (HOPG) This material has a capacitance that is an order of magnitude lower than both standard metals and theoretical expectations. Here, we use new quantum mechanical calculations in combination with a critical analysis of the literature to demonstrate that the standard explanations of this unusually low capacitance are inadequate. We then demonstrate that a layer of hydrocarbon impurities which has recently been shown to form on graphite is the most plausible explanation. We develop a model of this effect which accounts for the penetration of solvent into the hydrocarbon layer as the voltage increases. This model explains the characteristic V shape of the capacitance as a function of voltage. Finally, we present evidence that this layer also forms and limits the capacitance in real supercapacitor materials such as activated carbon. Methods of modifying or removing this layer could therefore potentially lead to significant improvements in the capacitance of typical supercapacitors.


activated carbon


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.