A series of experiments have been carried out inside of the environmental chamber with temperature ranging from 273 to 313 K for aqueous electrolyte and 263 to 333 K for organic electrolyte. The AC electrochemical cells have been tested using cycling voltammetry (CV) at 25 mV/s sweep rate. This was followed by the step potential electrochemical spectroscopy (SPECS) experiment with a 25 mV potential step and 300 s equilibration time.
SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window. This method has been used to effectively differentiate the charge storage contributions from electrical double layer capacitance at the geometric and porous surface areas and diffusion-limited capacitance as a function of scan rate [1].
The outcome of this work indicates the systematic effects of changes in temperature on different charge storage mechanisms. It was expected that the overall electrochemical performance of AC electrochemical cell increases by increasing the temperature in both aqueous and non-aqueous electrolytes, due to increase of kinetic energy of ions in solvent. However, different charge storage mechanism behaved differently in the aqueous and non-aqueous electrolytes. Figure 1. shows the comparison for CV tests (a) in aqueous and (b) in organic electrolytes at different temperatures.
It was found that, the total specific capacitance of AC electrochemical cell is increased by increasing the temperature in aqueous electrolyte. While, in non-aqueous electrolyte, the total specific capacitance decreases by increasing the temperature.
Additionally, SPECS method was used to obtain the contribution of different charge storage mechanisms at different temperatures. The result indicates that the electrical double layer and diffusion limited processes behaved differently in each electrolyte. For instance the capacitance contribution from diffusion-limited processes decreases by increasing the temperature while, the electrical double layer capacitance at the geometric and porous surface areas increases by increasing the temperature in aqueous electrolyte.
Finally, the specific capacitance obtained by the SPECS method was used to obtain the performance of the AC electrochemical cell in the aqueous and non-aqueous electrolytes in the form of a Ragone diagram.
[1]. Marveh Forghani and Scott W. Donne, Journal of the Electrochemical Society 2018 165: A664-A673.