Propping the Electrochemical Impedance Spectra at Different Voltages Reveals the Untapped Supercapacitive Performance of Materials

Electrochemical impedance spectroscopy (EIS) is one of the most powerful and universal techniques that provides deep insights into the nature of the electrochemical system and its performance and limitations. Electric double layer capacitors (EDLCs) are electrochemical devices that can deliver and store large amounts of energy compared to traditional capacitors. The selection of an electrolyte is critical to the overall performance of EDLCs as it strongly influences the internal resistance, operating potential window, and rate capability of the device. Herein, fullerene C 76 is investigated in four different electrolyte systems (Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , and Rb 2 SO 4 ) to reveal the crucial role of the electrolyte cation on the electrochemical supercapacitive performance. The Stern layer and diffuse layer formation are theorized for the electrolytes and comprehensively analysed to identify the electrolyte that provides the best system for high capacitive output. Rb + is found to have the best conductivity and is the most responsive to applied potentials. Specifically, monitoring the EIS of the system at different applied voltages enables the unveiling of the ongoing electrochemical processes and the charge storage mechanism in detail. This approach can be generalized for various electrochemical energy storage systems to help design efficient systems and unveil the working mechanisms.