Electrochemical Functionalization of Porous Materials for Supercapacitor Applications

Abstract

Aqueous supercapacitors are essential for meeting sustainable energy storage needs, offering enhanced safety, low cost, and high power performance. However, their low energy density limits their competitiveness against batteries, driving the need for research to extend their voltage range. This limitation arises from the interaction between the aqueous electrolyte and the carbon electrode, which triggers parasitic reactions such as water oxidation, water reduction, and carbon oxidation. These reactions currently limit the voltage range to 1.2 V. Parasitic reactions result from electron transfer between the electrode and the electrolyte. One potential solution to increase the voltage range is to form a passivating layer at the electrode-electrolyte interface, which permits ion transport while maintaining capacitance. To achieve this, diazonium salts are electrochemically grafted onto the electrode surface 2 . Fluorinated diazonium salts, in particular, are selected due to their ability to create hydrophobic surfaces, preventing water molecule interactions with the surface of the electrode. The initial study aims to understand how the geometry of the diazonium molecules—such as the position or length of substituents—affects the thickness and properties of the grafted films 3 . Various characterizations, including electrochemical analysis, XPS, and contact angle measurements, were performed. The grafting process was applied to porous carbon electrodes. A self-supporting electrode without Teflon, combining nanotubes and activated carbon was fabricated, exhibiting high electronic conductivity and capacitance. Then, the capacitance and the rated voltage of electrografted electrodes was tested in 0.5 MLi 2 SO 4 . --------------------------------- 1 Renewable and Sustainable Energy Reviews. 2018 Jan;81:1868–78. ²J Phys Chem B. 2005 Dec 1;109(51):24401–10. 3 Langmuir. 2009 Jan 6;25(1):286–93. Figure 1