Redox-Active Aqueous Electrolytes for Carbon Electrodes

1 Redox-Active Aqueous Electrolytes for Carbon Electrodes 

One typical redox pair example is iodide/iodine, and Lota and Frackowiak [909] applied the iodide/iodine redox pair for redox-active aqueous electrolytes of carbon-based ESs. An extremely high capacitance value of 1840 F g- was obtained for the carbon positive electrode in 1 M KI electrolyte. The following reactions (Equations 2.12 through 2.15) occur in this electrolyte, contributing to the pseudocapacitance [909]  

FIGURE 2.91 Voltammetry curve at 5 mV s scan rate for carbon ACl in 1 M KI solution. Potentials of both electrodes are measured separately versus saturated calomel electrode. (Reprinted from Electrochemistry Communications, 11, Lota, G., and E. Frackowiak, Striking capacitance of carbon/iodide interface, 87-90, Copyright 2009, with permission from Elsevier.) 

50 A g was obtained for two-electrode ES based on KI electrolyte. Senthilkumar et al. [910] found the addition of 0.08 M Kl into the 1M H2SO4 electrolyte led to nearly two-fold increase of the specific capacitance and energy density of the AC-based ES compared to the 1 M H2SO4 without KI. In comparison, the 0.08 M KI + 1 M Na2S04 and 0.08 M KBr + 1 M H2SO4 electrolytes resulted in a lower specific capacitance and energy density. 

FIGURE 2.92 Capacitance values of the positive carbon electrode estimated from the voltammetry characteristics at 5 mV s in the different alkali metal iodide solutions. (Reprinted bom Electrochemistry Communications, 13, Lota, G., K. Fic, and E. Frackowiak, Alkali metal iodide/carbon interface as a source of pseudocapacitance, 38-41, Copyright 2011, with permission from Elsevier.) 

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