Coupling of Differential Double-Layer and Pseudocapacitance

In Section 3.2.1, the ideal coupling of double-layer and pseudocapacitance was discussed briefly. In practice, one important factor to consider when looking to optimize capacitance is the interaction between faradic charge transfer and double-layer charge storage. In general, it has been shown theoretically that coupling between the two capacitive types is possible [1,33,34]. 

Coupling effects are much more pronounced for carbon electrodes that contain small amounts of surface functionality. These functionalities can induce a clear pseudocapacitive component that significantly boosts capacitance even for carbons with lower smface areas. Heteroatom functional groups induced by specific carbonization procedures or doping reactions 

Analyses of some carbon materials show the clearest case of coupling with a pseudocapacitive component when exposed to an acidic or basic electrolyte. Oxygen groups known to contribute to capacitance include redox pairs 

Dependence of conductivity on potential state for nitrogen-rich carbon material in acidic and neutral electrolyte media. (Source Poliak, E., G. Salitra, and D. Aurbach. 2007. Journal of Electroanalytical Chemistry, 602,195-202. With permission.) 

Electrosorption redox for nitrogen-carbon functionalities that contribute to pseudocapacitive peaks seen in acidic electrolyte. = presence of carbon network. (Sources Beguin, R, E. Raymundo-Pinero, and E. Frackowiak. 2010. Asymmetric systems. In Electrical Double-Layer Capacitors and Pseudocapacitors, 358-372 Frackowiak, E. et al. 2006. Electrochimica Acta, 51,2209-2214. With permission.) 

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